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Bindels RJ, Hartog A, Timmermans JA, van Os CH. Immunocytochemical localization of calbindin-D28k, calbindin-D9k and parvalbumin in rat kidney. Contrib Nephrol 2015; 91:7-13. [PMID: 1800013 DOI: 10.1159/000420150] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Possible sites involved in active Ca2+ transport were traced by means of immunocytochemical detection of calcium-binding proteins (CaBP) in the mammalian kidney. Antisera were raised in rabbits against calbindin-D28k from chick kidney and calbindin-D9k from bovine intestine and parvalbumin from rabbit muscle. In the rat kidney, parvalbumin and calbindin-D9k were co-localized in the loops of Henle and distal convoluted tubule. In the collecting duct their presence was restricted to the intercalated cells. In all responsive cells parvalbumin and calbindin-D9k were present exclusively along the basolateral membrane. Calbindin-D28k was only present in the outer part of the cortex, where it was localized in the distal convoluted tubule and in the connecting tubule. In these cells calbindin-D28k was evenly distributed through the cytosol. Calbindin-D28k, unlike parvalbumin and calbindin-D9k, could not be demonstrated in the loops of Henle or collecting duct.
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Affiliation(s)
- R J Bindels
- Department of Physiology, University of Nijmegen, The Netherlands
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2
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van Angelen AA, San-Cristobal P, Pulskens WP, Hoenderop JG, Bindels RJ. The impact of dietary magnesium restriction on magnesiotropic and calciotropic genes. Nephrol Dial Transplant 2013; 28:2983-93. [DOI: 10.1093/ndt/gft358] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
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3
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Glaudemans B, van der Wijst J, Scola R, Lorenzoni PJ, Heister A, van der Kemp A, Knoers NV, Hoenderop JG, Bindels RJ. Rare but Relevant Kidney Disorders. Clin J Am Soc Nephrol 2009. [DOI: 10.2215/01.cjn.0000927056.12668.a8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/28/2023]
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4
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Grünfeld JP, Scholl UI, Bockenhauer D, Glaudemans B, van Bommel EF, Scheel PJ, Delvaeye M, Choi M, Liu T, Ramaekers VT, Häusler MG, Grimmer J, Tobe SW, Farhi A, Nelson-Williams C, Lifton RP, Feather S, Stanescu HC, Bandulik S, Zdebik AA, Reichold M, Tobin J, Lieberer E, Sterner C, Landoure G, Arora R, Sirimanna T, Thompson D, Cross JH, van't Hoff W, Al Masri O, Tullus K, Yeung S, Anikster Y, Klootwijk E, Hubank M, Dillon MJ, Heitzmann D, Arcos-Burgos M, Knepper MA, Dobbie A, Gahl WA, Warth R, Sheridan E, Kleta R, van der Wijst J, Scola R, Lorenzoni PJ, Heister A, van der Kemp A, Knoers NV, Hoenderop JG, Bindels RJ, Jansen I, Hendriksz TR, Aarnoudse AL, Feeley N, Noris M, De Vriese A, Esmon CT, Esmon NL, Ferrell G, Del-Favero J, Plaisance S, Claes B, Lambrechts D, Remuzzi G, Conway EM. Rare but Relevant Kidney DisordersSeizures, sensorineural deafness, ataxia, mental retardation, and electrolyte imbalance (SeSAME syndrome) caused by mutations in KCNJ10. Proc Natl Acad Sci U S A 106: 5842–5847, 2009Epilepsy, ataxia, sensorineural deafness, tubulopathy, and KCNJ10 mutations. N Engl J Med 360: 1960–1970, 2009A missense mutation in the Kv1.1 voltage-gated potassium channel-encoding gene KCNA1 is linked to human autosomal dominant hypomagnesemia. J Clin Invest 119: 936–942, 2009Idiopathic retroperitoneal fibrosis: Prospective evaluation of incidence and clinicoradiologic presentation. Medicine 88: 193–201, 2009Retroperitoneal fibrosis: The clinical, laboratory, and radiographic presentation. Medicine 88: 202–207, 2009Thrombomodulin mutations in atypical hemolytic-uremic syndrome. N Engl J Med 361: 345–357, 2009. Clin J Am Soc Nephrol 2009. [DOI: 10.2215/cjn.06710909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Lu P, Boros S, Chang Q, Bindels RJ, Hoenderop JG. The -glucuronidase klotho exclusively activates the epithelial Ca2+ channels TRPV5 and TRPV6. Nephrol Dial Transplant 2008; 23:3397-402. [DOI: 10.1093/ndt/gfn291] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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6
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Abstract
Blood calcium concentration is maintained within a narrow range despite large variations in dietary input and body demand. The Transient Receptor Potential ion channel TRPV5 has been implicated in this process. We report here that TRPV5 is stimulated by the mammalian hormone klotho. Klotho, a beta-glucuronidase, hydrolyzes extracellular sugar residues on TRPV5, entrapping the channel in the plasma membrane. This maintains durable calcium channel activity and membrane calcium permeability in kidney. Thus, klotho activates a cell surface channel by hydrolysis of its extracellular N-linked oligosaccharides.
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Affiliation(s)
- Q Chang
- Department of Physiology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, 6500 HB Nijmegen, Netherlands
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7
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Voets T, Prenen J, Fleig A, Vennekens R, Watanabe H, Hoenderop JG, Bindels RJ, Droogmans G, Penner R, Nilius B. CaT1 and the calcium release-activated calcium channel manifest distinct pore properties. J Biol Chem 2001; 276:47767-70. [PMID: 11687570 DOI: 10.1074/jbc.c100607200] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The calcium release-activated calcium channel (CRAC) is a highly Ca(2+)-selective ion channel that is activated on depletion of inositol triphosphate (IP(3))-sensitive intracellular Ca(2+) stores. It was recently reported that CaT1, a member of the TRP family of cation channels, exhibits the unique biophysical properties of CRAC, which led to the conclusion that CaT1 comprises all or part of the CRAC pore (Yue, L., Peng, J. B., Hediger, M. A., and Clapham, D. E. (2001) Nature 410, 705-709). Here, we directly compare endogenous CRAC with heterologously expressed CaT1 and show that they manifest several clearly distinct properties. CaT1 can be distinguished from CRAC in the following features: sensitivity to store-depleting agents; inward rectification in the absence of divalent cations; relative permeability to Na(+) and Cs(+); effect of 2-aminoethoxydiphenyl borate (2-APB). Moreover, CaT1 displays a mode of voltage-dependent gating that is fully absent in CRAC and originates from the voltage-dependent binding/unbinding of Mg(2+) inside the channel pore. Our results imply that the pores of CaT1 and CRAC are not identical and indicate that CaT1 is a Mg(2+)-gated channel not directly related to CRAC.
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Affiliation(s)
- T Voets
- Laboratory of Physiology, Catholic University of Leuven, B-3000 Leuven, Belgium.
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8
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Hoenderop JG, Vennekens R, Müller D, Prenen J, Droogmans G, Bindels RJ, Nilius B. Function and expression of the epithelial Ca(2+) channel family: comparison of mammalian ECaC1 and 2. J Physiol 2001; 537:747-61. [PMID: 11744752 PMCID: PMC2278984 DOI: 10.1111/j.1469-7793.2001.00747.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
1. The epithelial Ca(2+) channel (ECaC) family represents a unique group of Ca(2+)-selective channels that share limited homology to the ligand-gated capsaicin receptors, the osmolarity-sensitive channel OTRPC4, as well as the transient receptor potential family. Southern blot analysis demonstrated that this family is restricted to two members, ECaC1 and ECaC2 (also named CaT1). 2. RT-PCR analysis demonstrated that the two channels are co-expressed in calbindin-D-containing epithelia, including small intestine, pancreas and placenta, whereas kidney and brain only express ECaC1 and stomach solely ECaC2. 3. From an electrophysiological point of view, ECaC1 and ECaC2 are highly similar channels. Differences concern divalent cation permeability, the kinetics of Ca(2+)-dependent inactivation and recovery from inactivation. 4. Ruthenium red is a potent blocker of ECaC activity. Interestingly, ECaC2 has a 100-fold lower affinity for ruthenium red (IC(50) 9 +/- 1 microM) than ECaC1 (IC(50) 121 +/- 13 nM). 5. ECaCs are modulated by intracellular Mg(2+) and ATP. ECaC1 and ECaC2 activity rapidly decay in the absence of intracellular ATP. This effect is further accelerated at higher intracellular Mg(2+) concentrations. 6. In conclusion, ECaC1 and ECaC2 are homologous channels, with an almost identical pore region. They can be discriminated by their sensitivity for ruthenium red and show differences in Ca(2+)-dependent regulation.
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Affiliation(s)
- J G Hoenderop
- Department of Cell Physiology, Institute of Cellular Signalling, University Medical Centre Nijmegen, The Netherlands
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Loffing J, Loffing-Cueni D, Valderrabano V, Kläusli L, Hebert SC, Rossier BC, Hoenderop JG, Bindels RJ, Kaissling B. Distribution of transcellular calcium and sodium transport pathways along mouse distal nephron. Am J Physiol Renal Physiol 2001; 281:F1021-7. [PMID: 11704552 DOI: 10.1152/ajprenal.0085.2001] [Citation(s) in RCA: 269] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The organization of Na(+) and Ca(2+) transport pathways along the mouse distal nephron is incompletely known. We revealed by immunohistochemistry a set of Ca(2+) and Na(+) transport proteins along the mouse distal convolution. The thiazide-sensitive Na(+)-Cl(-) cotransporter (NCC) characterized the distal convoluted tubule (DCT). The amiloride-sensitive epithelial Na(+) channel (ENaC) colocalized with NCC in late DCT (DCT2) and extended to the downstream connecting tubule (CNT) and collecting duct (CD). In early DCT (DCT1), the basolateral Ca(2+)-extruding proteins [Na(+)/Ca(2+) exchanger (NCX), plasma membrane Ca(2+)-ATPase (PCMA)] and the cytoplasmic Ca(2+)-binding protein calbindin D(28K) (CB) were found at very low levels, whereas the cytoplasmic Ca(2+)/Mg(2+)-binding protein parvalbumin was highly abundant. NCX, PMCA, and CB prevailed in DCT2 and CNT, where we located the apical epithelial Ca(2+) channel (ECaC1). Its subcellular localization changed from apical in DCT2 to exclusively cytoplasmic at the end of CNT. NCX and PMCA decreased in parallel with the fading of ECaC1 in the apical membrane. All three of them were undetectable in CD. These findings disclose DCT2 and CNT as major sites for transcellular Ca(2+) transport in the mouse distal nephron. Cellular colocalization of Ca(2+) and Na(+) transport pathways suggests their mutual interactions in transport regulation.
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Affiliation(s)
- J Loffing
- Institute of Anatomy, University of Zurich, CH-8057 Zurich.
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10
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Van Cromphaut SJ, Dewerchin M, Hoenderop JG, Stockmans I, Van Herck E, Kato S, Bindels RJ, Collen D, Carmeliet P, Bouillon R, Carmeliet G. Duodenal calcium absorption in vitamin D receptor-knockout mice: functional and molecular aspects. Proc Natl Acad Sci U S A 2001; 98:13324-9. [PMID: 11687634 PMCID: PMC60869 DOI: 10.1073/pnas.231474698] [Citation(s) in RCA: 475] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Rickets and hyperparathyroidism caused by a defective vitamin D receptor (VDR) can be prevented in humans and animals by high calcium intake, suggesting that intestinal calcium absorption is critical for 1,25(OH)(2) vitamin D [1,25(OH)(2)D(3)] action on calcium homeostasis. We assessed the rate of serum (45)Ca accumulation within 10 min of oral gavage in two strains of VDR-knockout (KO) mice (Leuven and Tokyo KO) and observed a 3-fold lower area under the curve in both KO strains. Moreover, we evaluated the expression of intestinal candidate genes involved in transcellular calcium transport. The calcium transport protein1 (CaT1) was more abundantly expressed at mRNA level than the epithelial calcium channel (ECaC) in duodenum, but both were considerably reduced (CaT1>90%, ECaC>60%) in the two VDR-KO strains on a normal calcium diet. Calbindin-D(9K) expression was decreased only in the Tokyo KO, whereas plasma membrane calcium ATPase (PMCA(1b)) expression was normal in both VDR-KOs. In Leuven wild-type mice, a high calcium diet inhibited (>90%) and 1,25(OH)(2)D(3) injection or low calcium diet induced (6-fold) duodenal CaT1 expression and, to a lesser degree, ECaC and calbindin-D(9K) expression. In Leuven KO mice, however, high or low calcium intake decreased calbindin-D(9K) and PMCA(1b) expression, whereas CaT1 and ECaC expression remained consistently low on any diet. These results suggest that the expression of the novel duodenal epithelial calcium channels (in particular CaT1) is strongly vitamin D-dependent, and that calcium influx, probably interacting with calbindin-D(9K), should be considered as a rate-limiting step in the process of vitamin D-dependent active calcium absorption.
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Affiliation(s)
- S J Van Cromphaut
- Laboratory of Experimental Medicine and Endocrinology, Katholieke Universiteit Leuven, Leuven, B-3000 Belgium
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11
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Nilius B, Prenen J, Vennekens R, Hoenderop JG, Bindels RJ, Droogmans G. Pharmacological modulation of monovalent cation currents through the epithelial Ca2+ channel ECaC1. Br J Pharmacol 2001; 134:453-62. [PMID: 11588099 PMCID: PMC1572972 DOI: 10.1038/sj.bjp.0704272] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. The recent identification of the epithelial Ca(2+) channel, ECaC1, represents a major step forward in our knowledge of renal Ca(2+) handling. ECaC1 constitutes the rate-limiting apical Ca(2+) entry mechanism of active, transcellular Ca(2+) reabsorption. This unique highly selective Ca(2+) channel shares a low but significant homology with transient receptor potential (TRP) channels and vanilloid receptors (VR). 2. We have studied the pharmacological modulation of currents through ECaC1 heterologously expressed in HEK 293 cells. Monovalent cation currents were measured by use of the whole cell patch clamp technique in cells dialysed with 10 mM BAPTA or 10 mM EGTA to prevent the fast Ca(2+) dependent inactivation of ECaC1. 3. Several modulators were tested, including inorganic cations, putative store-operated Ca(2+) entry (SOC) blockers, the vanilloid receptor (VR-1) blocker capsazepine, protein tyrosine kinase blockers, calmodulin antagonists and ruthenium red. 4. Ruthenium red and econazole appeared to be the most effective inhibitors of currents through ECaC1, with IC(50) values of 111 nM and 1.3 microM, respectively, whereas the selective SOC inhibitor, SKF96365, was nearly ineffective. 5. The divalent cation current block profile for ECaC1 is Pb(2+)=Cu(2+) >Zn(2+) >Co(2+) >Fe(2+) with IC(50) values between 1 and approximately 10 microM. 6. In conclusion, ECaC activity is effectively inhibited by various compounds including ruthenium red, antimycotic drugs and divalent cations, which might be useful tools for pharmacological manipulation and several disorders related to Ca(2+) homeostasis could benefit from such developments.
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Affiliation(s)
- B Nilius
- Department of Physiology, Campus Gasthuisberg, KU Leuven, Belgium.
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12
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Dijkink L, Hartog A, Van Os CH, Bindels RJ. Modulation of aldosterone-induced stimulation of ENaC synthesis by changing the rate of apical Na+ entry. Am J Physiol Renal Physiol 2001; 281:F687-92. [PMID: 11553516 DOI: 10.1152/ajprenal.2001.281.4.f687] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Primary cultures of immunodissected rabbit connecting tubule and cortical collecting duct cells were used to investigate the effect of apical Na+ entry rate on aldosterone-induced transepithelial Na+ transport, which was measured as benzamil-sensitive short-circuit current (I(sc)). Stimulation of the apical Na+ entry, by long-term short-circuiting of the monolayers, suppressed the aldosterone-stimulated benzamil-sensitive I(sc) from 320 +/- 49 to 117 +/- 14%, whereas in the presence of benzamil this inhibitory effect was not observed (335 +/- 74%). Immunoprecipitation of [(35)S]methionine-labeled beta-rabbit epithelial Na+ channel (rbENaC) revealed that the effects of modulation of apical Na+ entry on transepithelial Na+ transport are exactly mirrored by beta-rbENaC protein levels, because short-circuiting the monolayers decreased aldosterone-induced beta-rbENaC protein synthesis from 310 +/- 51 to 56 +/- 17%. Exposure to benzamil doubled the beta-rbENaC protein level to 281 +/- 68% in control cells but had no significant effect on aldosterone-stimulated beta-rbENaC levels (282 +/- 68%). In conclusion, stimulation of apical Na+ entry suppresses the aldosterone-induced increase in transepithelial Na+ transport. This negative-feedback inhibition is reflected in a decrease in beta-rbENaC synthesis or in an increase in beta-rbENaC degradation.
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Affiliation(s)
- L Dijkink
- Department of Cell Physiology, University Medical Centre Nijmegen, 6500 HB Nijmegen, The Netherlands
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13
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Koopman WJ, Scheenen WJ, Errington RJ, Willems PH, Bindels RJ, Roubos EW, Jenks BG. Membrane-initiated Ca(2+) signals are reshaped during propagation to subcellular regions. Biophys J 2001; 81:57-65. [PMID: 11423394 PMCID: PMC1301491 DOI: 10.1016/s0006-3495(01)75679-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
An important aspect of Ca(2+) signaling is the ability of cells to generate intracellular Ca(2+) waves. In this study we have analyzed the cellular and subcellular kinetics of Ca(2+) waves in a neuroendocrine transducer cell, the melanotrope of Xenopus laevis, using the ratiometric Ca(2+) probe indo-1 and video-rate UV confocal laser-scanning microscopy. The purpose of the present study was to investigate how local Ca(2+) changes contribute to a global Ca(2+) signal; subsequently we quantified how a Ca(2+) wave is kinetically reshaped as it is propagated through the cell. The combined kinetics of all subcellular Ca(2+) signals determined the shape of the total cellular Ca(2+) signal, but each subcellular contribution to the cellular signal was not constant in time. Near the plasma membrane, [Ca(2+)](i) increased and decreased rapidly, processes that can be described by a linear and exponential function, respectively. In more central parts of the cell slower kinetics were observed that were best described by a Hill equation. This reshaping of the Ca(2+) wave was modeled with an equation derived from a low-pass RC filter. We propose that the differences in spatial kinetics of the Ca(2+) signal serves as a mechanism by which the same cellular Ca(2+) signal carries different regulatory information to different subcellular regions of the cell, thus evoking differential cellular responses.
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Affiliation(s)
- W J Koopman
- Department of Cellular Animal Physiology, University of Nijmegen, Nijmegen, The Netherlands
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14
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Nilius B, Prenen J, Vennekens R, Hoenderop JG, Bindels RJ, Droogmans G. Modulation of the epithelial calcium channel, ECaC, by intracellular Ca2+. Cell Calcium 2001; 29:417-28. [PMID: 11352507 DOI: 10.1054/ceca.2001.0201] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We have studied the modulation by intracellular Ca2+ of the epithelial Ca2+ channel, ECaC, heterologously expressed in HEK 293 cells. Whole-cell and inside-out patch clamp current recordings were combined with FuraII-Ca2+ measurements:1. Currents through ECaC were dramatically inhibited if Ca2+ was the charge carrier. This inhibition was dependent on the extracellular Ca2+ concentration and occurred also in cells buffered intracellularly with 10 mM BAPTA.2. Application of 30 mM [Ca(2)]e induced in non-Ca2+] buffered HEK 293 cells at -80 m V an increase in intracellular Ca2+([Ca2]i) with a maximum rate of rise of 241 +/-15nM/s (n= 18 cells) and a peak value of 891 +/- 106 nM. The peak of the concomitant current with a density of 12.3 +/- 2.6 pA/pF was closely correlated with the peak of the first-time derivative of the Ca2+ transient, as expected if the Ca2+ transient is due to influx of Ca2+. Consequently, no Ca2+] signal was observed in cells transfected with the Ca2+ impermeable ECaC mutant, D542A, in which an aspartate in the pore region was neutralized.3. Increasing [Ca2+]i by dialyzing the cell with pipette solutions containing various Ca2+] concentrations, all buffered with 10 mM BAPTA, inhibited currents through ECaC carried by either Na+ or Ca2+] ions. Half maximal inhibition of Ca(2+)currents in the absence of monovalent cations occurred at 67 nM (n between 6 and 8), whereas Na+ currents in the absence of Ca2+] and Mg2+ were inhibited with an IC50 of 89 nM (n between 6 and 10). Currents through ECaC in the presence of 1 mM Ca2+ and Na+, which are mainly carried by Ca2+, are inhibited by [Ca2]i with an IC50of 82 nM (n between 6 and 8). Monovalent cation currents through the Ca2+impermeable D542A ECaC mutant were also inhibited by an elevation of [Ca2]i (IC50 = 123 nM, n between 7 and 18). 4. The sensitivity of ECaC currents in inside-out patches for [Ca2]i was slightly shifted to higher concentrations as compared with whole cell measurements. Half-maximal inhibition occurred at 169 nM if Na+ was the charge carrier (n between 4 and 11) and 228 nM at 1 mM [Ca2]e (n between 4 and 8).5. Recovery from inhibition upon washout of extracellular Ca2+ (whole-cell configuration) or removal of Ca2+ from the inner side of the channel (inside-out patches) was slow in both conditions. Half-maximal recovery was reached after 96 +/- 34 s (n= 15) in whole-cell mode and after 135 +/- 23 s (n = 17) in inside-out patches.6. We conclude that influx of Ca2+ through ECaC and [Ca2]i induce feedback inhibition of ECaC currents, which is controlled by the concentration of Ca2+ in a micro domain near the inner mouth of the channel. Slow recovery seems to depend on dissociation of Ca( 2+ from an internal Ca2+ binding site at ECaC.
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Affiliation(s)
- B Nilius
- Department of Physiology, Campus Gasthuisberg, KU Leuven, Leuven, Belgium.
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15
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Abstract
We investigated the effect of extracellular pH on whole-cell currents through the epithelial Ca2+ channel, ECaC, expressed in HEK 293 cells. Both mono- and divalent current densities were significantly smaller at pH 6.0 than at pH 7.4. At pH 8.5 they were slightly larger. Lowering extracellular pH enhanced the slow component of monovalent current activation at negative potentials but had no significant effect on the kinetics of Ca2+ currents. The kinetics of block of monovalent cation current by extracellular Mg2+ was significantly changed at high and low pH. The time constant of the time- and voltage-dependent current component during a voltage step to -140 mV was significantly larger at pH 8.5 than at pH 7.4. At pH 6.0 it was almost absent. The [Mg2+] inhibiting 50% of monovalent current through ECaC at pH 6.0 (IC50) was 323 +/- 23 microM (n = 8), compared with 62 +/- 9 microM (n = 4) at pH 7.4 and 38 +/- 4 microM (n = 8) at pH 8.5. The affinity of ECaC for Ca2+ was also affected by extracellular pH, shifting from 4.8 +/- 0.7 microM (n = 6) at pH 6.0 to 161 +/- 30 nM (n = 5) at pH 7.4 and 425 +/- 117 nM (n = 8) at pH 8.5.
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Affiliation(s)
- R Vennekens
- Department of Physiology, Campus Gasthuisberg, KU Leuven, Herestraat 49, 3000 Leuven, Belgium
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16
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Bosch RR, Hoenderop JG, van der Heijden L, De Pont JJ, Bindels RJ, Willems PH. Hormonal regulation of phospholipase D activity in Ca(2+) transporting cells of rabbit connecting tubule and cortical collecting duct. Biochim Biophys Acta 2001; 1538:329-38. [PMID: 11336804 DOI: 10.1016/s0167-4889(01)00084-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Phospholipase D (PLD) is distributed widely in mammalian tissues where it is believed to play an important role in the regulation of cell functions and cell fate by a variety of extracellular signals. In this study, we used primary cultures of rabbit connecting tubule (CNT) and cortical collecting duct (CCD) cells, grown to confluence on a permeable support, to investigate the possible involvement of PLD in the mechanism of action of hormones that regulate Ca(2+) reabsorption. RT-PCR revealed the presence of transcripts of PLD1b and PLD2, but not PLD1a, in these cultures. Moreover, the expression of substantial amounts of PLD1 protein was demonstrated by Western blotting. To measure PLD activity, cells were labelled with [(3)H]myristic acid after which the PLD-catalysed formation of radiolabelled phosphatidylethanol ([(3)H]PtdEth) was measured in the presence of 1% (v/v) ethanol. Deamino-Cys,D-Arg(8)-vasopressin (dDAVP) and N(6)-cyclopentyladenosine (CPA), two potent stimulators of Ca(2+) transport across these monolayers, stimulated PLD activity as was indicated by a marked increase in [(3)H]PtdEth. Similarly, ATP, a potent inhibitor of dDAVP- and CPA-stimulated Ca(2+) transport, increased the formation of [(3)H]PtdEth. PLD activity was furthermore increased by 8Br-cAMP and following acute (30 min) stimulation of protein kinase C (PKC) with a phorbol ester (PMA). Chronic PMA treatment (120 h) to downregulate phorbol ester-sensitive PKC isoforms did not affect PLD activation by dDAVP, CPA and 8Br-cAMP, while markedly decreasing the effect of ATP and abolishing the effect of PMA. The PKC inhibitor chelerythrine significantly reduced PLD activation by dDAVP, CPA and 8Br-cAMP, without changing the effect of ATP. The inhibitor only partially reduced the effect of PMA. This study shows that Ca(2+) transporting cells of CNT and CCD contain a regulated PLD activity. The physiological relevance of this activity, which is not involved in Ca(2+) reabsorption, remains to be established.
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Affiliation(s)
- R R Bosch
- Department of Biochemistry, University Medical Centre Nijmegen, The Netherlands
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17
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Bindels RJ. Molecular pathophysiology of renal calcium handling. Kidney Blood Press Res 2001; 23:183-4. [PMID: 11031716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Affiliation(s)
- R J Bindels
- Cell Physiology, University of Nijmegen, The Netherlands
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18
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Vennekens R, Prenen J, Hoenderop JG, Bindels RJ, Droogmans G, Nilius B. Pore properties and ionic block of the rabbit epithelial calcium channel expressed in HEK 293 cells. J Physiol 2001; 530:183-91. [PMID: 11208967 PMCID: PMC2278408 DOI: 10.1111/j.1469-7793.2001.0183l.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
We have used the whole-cell patch-clamp technique to analyse the permeation properties and ionic block of the epithelial Ca2+ channel ECaC heterologously expressed in human embryonic kidney (HEK) 293 cells. Cells dialysed with 10 mM BAPTA and exposed to Ca2+-containing, monovalent cation-free solutions displayed large inwardly rectifying currents. Their reversal potential depended on the extracellular Ca2+ concentration, [Ca2+]o. The slope of the relationship between reversal potential and [Ca2+]o on a logarithmic scale was 21 +/- 4 mV, compared with 29 mV as predicted by the Nernst equation (n = 3-5 cells). Currents in mixtures of Ca2+ and Na+ or Ca2+ and Ba2+ showed anomalous mole fraction behaviour. We have described the current-concentration plot for Ca2+ and Na+ by a kinetic permeation model, i.e. the "step" model. Extracellular Mg2+ blocked both divalent and monovalent currents with an IC50 of 62 +/- 9 microM(n = 4) in Ca2+-free conditions and 328 +/- 50 microM (n = 4-9) in 100 microM Ca2+ solutions. Mono- and divalent currents through ECaCs were blocked by gadolinium, lanthanum and cadmium, with a blocking order of Cd2+ >> Gd3+ > La3+. We conclude that the permeation of monovalent and divalent cations through ECaCs shows similarities with L-type voltage-gated Ca2+ channels, the main differences being a higher Ca2+ affinity and a significantly higher current density in micromolar Ca2+ concentrations in the case of ECaCs.
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Affiliation(s)
- R Vennekens
- Department of Physiology, Campus Gasthuisberg, KULeuven, Leuven, Belgium
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19
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Nilius B, Vennekens R, Prenen J, Hoenderop JG, Droogmans G, Bindels RJ. The single pore residue Asp542 determines Ca2+ permeation and Mg2+ block of the epithelial Ca2+ channel. J Biol Chem 2001; 276:1020-5. [PMID: 11035011 DOI: 10.1074/jbc.m006184200] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The epithelial Ca(2+) channel (ECaC), which was recently cloned from rabbit kidney, exhibits distinctive properties that support a facilitating role in transcellular Ca(2+) (re)absorption. ECaC is structurally related to the family of six transmembrane-spanning ion channels with a pore-forming region between S5 and S6. Using point mutants of the conserved negatively charged amino acids present in the putative pore, we have identified a single aspartate residue that determines Ca(2+) permeation of ECaC and modulation by extracellular Mg(2+). Mutation of the aspartate residue, D542A, abolishes Ca(2+) permeation and Ca(2+)-dependent current decay as well as block by extracellular Mg(2+), whereas monovalent cations still permeate the mutant channel. Variation of the side chain length in mutations D542N, D542E, and D542M attenuated Ca(2+) permeability and Ca(2+)-dependent current decay. Block of monovalent currents through ECaC by Mg(2+) was decreased. Exchanging the aspartate residue for a positively charged amino acid, D542K, resulted in a nonfunctional channel. Mutations of two neighboring negatively charged residues, i.e. Glu(535) and Asp(550), had only minor effects on Ca(2+) permeation properties.
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Affiliation(s)
- B Nilius
- Department of Physiology, Campus Gasthuisberg, KU Leuven, Leuven B-3000, Belgium.
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20
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Meij IC, Koenderink JB, van Bokhoven H, Assink KF, Groenestege WT, de Pont JJ, Bindels RJ, Monnens LA, van den Heuvel LP, Knoers NV. Dominant isolated renal magnesium loss is caused by misrouting of the Na(+),K(+)-ATPase gamma-subunit. Nat Genet 2000; 26:265-6. [PMID: 11062458 DOI: 10.1038/81543] [Citation(s) in RCA: 204] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Primary hypomagnesaemia is composed of a heterogeneous group of disorders characterized by renal or intestinal Mg(2+) wasting, often associated with disturbances in Ca(2+) excretion. We identified a putative dominant-negative mutation in the gene encoding the Na(+), K(+)-ATPase gamma-subunit (FXYD2), leading to defective routing of the protein in a family with dominant renal hypomagnesaemia.
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Affiliation(s)
- I C Meij
- Department of Pediatrics, Institute of Cellular Signaling, University Medical Centre Nijmegen, Nijmegen, The Netherlands
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21
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Nilius B, Vennekens R, Prenen J, Hoenderop JG, Bindels RJ, Droogmans G. Whole-cell and single channel monovalent cation currents through the novel rabbit epithelial Ca2+ channel ECaC. J Physiol 2000; 527 Pt 2:239-48. [PMID: 10970426 PMCID: PMC2270079 DOI: 10.1111/j.1469-7793.2000.00239.x] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
This study describes properties of monovalent cation currents through ECaC, a recently cloned epithelial Ca2+-permeable channel from rabbit. The kinetics of currents through ECaC was strongly modulated by divalent cations. Currents were inhibited in the presence of extracellular Ca2+. They showed an initial voltage-dependent decay in the presence of mM Mg2+ at hyperpolarizing steps in Ca2+-free solutions, which represents a voltage-dependent Mg2+ block through binding of Mg2+ to a site localized in the electrical field of the membrane (delta = 0.31) and a voltage-dependent binding constant (at 0 mV 3.1 mM Ca2+, obtained from a Woodhull type analysis). Currents were only stable in the absence of divalent cations and showed under these conditions a small time- and voltage-dependent component of activation. Single channel currents in cell-attached and inside-out patches had a conductance of 77.5 +/- 4.9 pS (n = 11) and reversed at +14.8 +/- 1. 6 11imV81i (n = 9) in the absence of divalent cations. The permeation sequence for monovalent cations through ECaC was Na+ > Li+ > K+ > Cs+ > NMDG+ which is identical to the Eisenmann sequence X for a strong field-strength binding site. It is concluded that the permeation profile of ECaC for monovalent cations suggests a strong field-strength binding site that may be involved in Ca2+ permeation and Mg2+ block.
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Affiliation(s)
- B Nilius
- Department of Physiology, Campus Gasthuisberg, Katholieke Universiteit, Leuven, Leuven, Belgium.
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22
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Müller D, Hoenderop JG, Merkx GF, van Os CH, Bindels RJ. Gene structure and chromosomal mapping of human epithelial calcium channel. Biochem Biophys Res Commun 2000; 275:47-52. [PMID: 10944439 DOI: 10.1006/bbrc.2000.3227] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The epithelial Ca(2+) channel, ECaC, represents the rate-limiting step of vitamin D(3)-regulated Ca(2+) (re)absorption in kidney and intestine, and provides, therefore, a new candidate gene for Ca(2+)-related disorders. To supply the basis for direct mutation analysis, we report here the structure of the human ECaC gene (ECAC1(2)). It consists of 16 exons spanning 25 kb with introns ranging from 98 to 8500 bp. The 5'-flanking region of ECAC1 contains four putative vitamin D(3)-responsive elements. At positions -92 and -13 transcription initiation sites were identified, but the former lacks the canonical TATA or CAAT boxes. ECAC1 was mapped to chromosome 7q35 by fluorescent in situ hybridization, reassigning a previous radiation hybrid mapping to 7q31.1-2. The gene of a recently identified rat intestine homologue of ECaC, named Ca(2+) transporter 1, was found juxtaposed to the ECaC gene, indicating that both genes are the products of evolutionary local gene duplication.
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Affiliation(s)
- D Müller
- Department of Cell Physiology, University Medical Center Nijmegen, HB Nijmegen, 6500, The Netherlands
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23
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Van Aubel RA, Hartog A, Bindels RJ, Van Os CH, Russel FG. Expression and immunolocalization of multidrug resistance protein 2 in rabbit small intestine. Eur J Pharmacol 2000; 400:195-8. [PMID: 10988333 DOI: 10.1016/s0014-2999(00)00391-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Multidrug resistance protein 2 (MRP2) is an ATP-dependent transporter of anionic drugs and conjugates. It functions as an efflux pump in the apical membranes of liver and kidney cells, but its membrane localization in small intestine has not yet been defined. The present study demonstrates exclusive localization of Mrp2 to the brush-border (apical) membrane of villi, decreasing in intensity from the villus tip to the crypts. In immunoblot analysis of crude membranes of various rabbit tissues, Mrp2 was only found in small intestine, kidney and liver. These results are in-line with the supposed function of Mrp2 in drug excretion.
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Affiliation(s)
- R A Van Aubel
- Department of Pharmacology and Toxicology, UMC St. Radboud, University of Nijmegen, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
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24
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Abstract
The epithelial calcium channel present in the apical membrane of 1,25-dihydroxyvitamin D3-responsive nephron segments represents the first member of a new family of calcium channels. This review covers the distinctive properties of this highly calcium-selective channel and highlights the implications for our understanding of the process of calcium reabsorption.
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Affiliation(s)
- J G Hoenderop
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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25
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Müller D, Hoenderop JG, Meij IC, van den Heuvel LP, Knoers NV, den Hollander AI, Eggert P, García-Nieto V, Claverie-Martín F, Bindels RJ. Molecular cloning, tissue distribution, and chromosomal mapping of the human epithelial Ca2+ channel (ECAC1). Genomics 2000; 67:48-53. [PMID: 10945469 DOI: 10.1006/geno.2000.6203] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Functional and morphological analyses indicated that the epithelial Ca2+ channel (ECaC), which was recently cloned from rabbit kidney, exhibits the defining properties for being the gatekeeper in transcellular Ca2+ (re)absorption. Its human homologue provides, therefore, a molecular basis for achieving a better understanding of Ca2+ mal(re)absorption. By applying the RACE technique, the full-length cDNA of human ECaC (HGMW-approved symbol ECAC1) was obtained. It consisted of 2,772 bp with an open reading frame of 2,187 bp encoding a protein of 729 amino acids with a predicted molecular mass of 83 kDa. Phylogenetic analysis indicated that this highly selective Ca2+ channel exhibits a low level of homology (<30%) to other Ca2+ channels, suggesting that it belongs to a new family. hECaC was highly expressed in kidney, small intestine, and pancreas, and less intense expression was detected in testis, prostate, placenta, brain, colon, and rectum. These ECaC-positive tissues also expressed the 1,25-dihydroxyvitamin D3-sensitive calcium-binding proteins, calbindin-D9K and/or calbindin-D28K. The human ECaC gene mapped to chromosome 7q31.1-q31.2. Taken together, the conspicuous colocalization of hECaC and calbindins in organs that are not prime regulators of plasma Ca2+ levels could illustrate new pathways in cellular Ca2+ homeostasis.
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Affiliation(s)
- D Müller
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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26
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Abstract
The fine tuning of Ca(2+) excretion in the kidney takes place in the distal nephron, which consists of the distal convoluted tubule, connecting tubule, and initial portion of the cortical collecting duct. In these segments, Ca(2+) is reabsorbed through an active transcellular pathway. The apical influx of Ca(2+) into the distal renal cell is presumably the rate-limiting step in this process, and its molecular identity has remained obscure so far. The recently discovered epithelial Ca(2+) channel (ECaC) exhibits the expected properties for being the gatekeeper in transcellular Ca(2+) reabsorption. The characteristics and potential physiological role of ECaC will be discussed in this review. Our knowledge of the mechanisms involved in the regulation of transcellular Ca(2+) transport has advanced rapidly since the development of cell models originating from distal tubular cells. Studies using these models indicate that hormones including arginine vasopressin, PGE(2), adenosine, ATP, and atrial natriuretic peptide should be considered as calciotropic hormones controlling renal Ca(2+) handling. Evidence is now beginning to emerge that the stimulating calciotropic hormones utilize new cAMP-independent pathways to stimulate Ca(2+) reabsorption. These new findings allow the development of a comprehensive and detailed model of the process of transcellular calcium transport in the kidney whereby the individual contribution of the participating transporters can now be fully appreciated.
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Affiliation(s)
- J G Hoenderop
- Department of Cell Physiology, Institute of Cellular Signalling, University of Nijmegen, The Netherlands
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27
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Vennekens R, Hoenderop JG, Prenen J, Stuiver M, Willems PH, Droogmans G, Nilius B, Bindels RJ. Permeation and gating properties of the novel epithelial Ca(2+) channel. J Biol Chem 2000; 275:3963-9. [PMID: 10660551 DOI: 10.1074/jbc.275.6.3963] [Citation(s) in RCA: 237] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The recently cloned epithelial Ca(2+) channel (ECaC) constitutes the Ca(2+) influx pathway in 1,25-dihydroxyvitamin D(3)-responsive epithelia. We have combined patch-clamp analysis and fura-2 fluorescence microscopy to functionally characterize ECaC heterologously expressed in HEK293 cells. The intracellular Ca(2+) concentration in ECaC-expressing cells was closely correlated with the applied electrochemical Ca(2+) gradient, demonstrating the distinctive Ca(2+) permeability and constitutive activation of ECaC. Cells dialyzed with 10 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid displayed large inward currents through ECaC in response to voltage ramps. The corresponding current-voltage relationship showed pronounced inward rectification. Currents evoked by voltage steps to potentials below -40 mV partially inactivated with a biexponential time course. This inactivation was less pronounced if Ba(2+) or Sr(2+) replaced Ca(2+) and was absent in Ca(2+)-free solutions. ECaC showed an anomalous mole fraction behavior. The permeability ratio P(Ca):P(Na) calculated from the reversal potential at 30 mM [Ca(2+)](o) was larger than 100. The divalent cation selectivity profile is Ca(2+) > Mn(2+) > Ba(2+) approximately Sr(2+). Repetitive stimulation of ECaC-expressing cells induced a decay of the current response, which was greatly reduced if Ca(2+) was replaced by Ba(2+) and was virtually abolished if [Ca(2+)](o) was lowered to 1 nM. In conclusion, ECaC is a Ca(2+) selective channel, exhibiting Ca(2+)-dependent autoregulatory mechanisms, including fast inactivation and slow down-regulation.
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Affiliation(s)
- R Vennekens
- Department of Physiology, Campus Gasthuisberg, Katholieke Universiteit Leuven, Leuven B-3000, Belgium
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28
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van Baal J, Hoenderop JG, Groenendijk M, van Os CH, Bindels RJ, Willems PH. Hormone-stimulated Ca2+ transport in rabbit kidney: multiple sites of inhibition by exogenous ATP. Am J Physiol 1999; 277:F899-906. [PMID: 10600937 DOI: 10.1152/ajprenal.1999.277.6.f899] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Exogenous ATP markedly reduced 1-desamino-8-D-arginine vasopressin (dDAVP)-stimulated Ca2+ transport and cAMP accumulation in primary cultures of rabbit connecting tubule and cortical collecting duct cells. Similarly, ATP inhibited the stimulatory effect of 8-bromo-cAMP. At first sight, this is in agreement with the "classic" concept that dDAVP exerts its stimulatory effect via cAMP. However, dDAVP-stimulated Ca2+ transport was markedly reduced by the protein kinase C (PKC) inhibitor chelerythrine, reported previously to inhibit the cAMP-independent pathway responsible for parathyroid hormone-, [Arg8]vasopressin-, PGE2-, and adenosine-stimulated Ca2+ transport. Chelerythrine also inhibited the increase in Ca2+ transport evoked by the cAMP-independent A1 receptor agonist N6-cyclopentyladenosine (CPA). Downregulation of phorbol ester-sensitive PKC isoforms by chronic phorbol ester treatment has been shown before to be without effect on hormone-stimulated Ca2+ transport, indicating that the chelerythrine-inhibitable pathway consists of a phorbol ester-insensitive PKC isoform. Here, this maneuver did not affect ATP inhibition of dDAVP-stimulated Ca2+ transport and cAMP formation, while abolishing ATP inhibition of CPA-stimulated Ca2+ transport. These findings show that ATP acts via 1) a phorbol ester-sensitive PKC isoform to inhibit hormonal stimulation of Ca2+ transport at the level of the chelerythrine-inhibitable pathway involving a phorbol ester-insensitive PKC isoform and 2) a phorbol ester-insensitive mechanism to inhibit V2 receptor-mediated concomitant activation of this pathway and adenylyl cyclase.
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Affiliation(s)
- J van Baal
- Department of Cell Physiology, University of Nijmegen, 6500 HB Nijmegen, The Netherlands
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29
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Hoenderop JG, van der Kemp AW, Hartog A, van Os CH, Willems PH, Bindels RJ. The epithelial calcium channel, ECaC, is activated by hyperpolarization and regulated by cytosolic calcium. Biochem Biophys Res Commun 1999; 261:488-92. [PMID: 10425212 DOI: 10.1006/bbrc.1999.1059] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The recently cloned epithelial Ca(2+) channel, ECaC, which is expressed in the apical membrane of 1,25-dihydroxyvitamin D(3)-responsible epithelia, was characterized in Xenopus laevis oocytes by measuring the Ca(2+)-activated Cl(-) current which is a sensitive read-out of the Ca(2+) influx. ECaC-expressing oocytes responded to a voltage ramp with a maximal inward current of -2.1 +/- 0.3 microA at a holding potential of -99 +/- 1 mV. The inward current decreased progressively at less negative potentials and at +50 mV a small Ca(2+)-induced outward current was observed. The Ca(2+) influx-evoked current at a hyperpolarizing pulse to -100 mV displayed a fast activation followed by a rapid but partial inactivation. Loading of the oocytes with the Ca(2+) chelator BAPTA delayed the activation and blocked the inactivation of ECaC. When a series of brief hyperpolarizing pulses were given a significant decline in the peak response and subsequent plateau phase was observed. In conclusion, the distinct electrophysiological features of ECaC are hyperpolarization-dependent activation, Ca(2+)-dependent regulation of channel conductance and desensitization during repetitive stimulation.
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Affiliation(s)
- J G Hoenderop
- Department of Cell Physiology, Institute of Cellular Signalling, Nijmegen, 6500 HB, The Netherlands
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30
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Dijkink L, Hartog A, Deen PM, van Os CH, Bindels RJ. Time-dependent regulation by aldosterone of the amiloride-sensitive Na+ channel in rabbit kidney. Pflugers Arch 1999; 438:354-60. [PMID: 10398866 DOI: 10.1007/s004240050920] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The epithelial Na+ channel (ENaC) functions as the rate-limiting factor in aldosterone-regulated transcellular Na+ transport. In the study described here, the effect of aldosterone on ENaC mRNA levels, protein synthesis and benzamil-sensitive Na+ transport was investigated using primary cultures of immunodissected rabbit kidney connecting tubule and cortical collecting duct cells (CNT and CCD, respectively). After a lag time of 3 h, aldosterone caused transepithelial Na+ transport to increase, reaching maximal level of 260+/-44% after 16 h of incubation. The alpha, beta and gamma rabbit ENaC (rbENaC) mRNA levels, measured by semi-quantitative reverse transcriptase-polymerase chain reaction, were not changed by aldosterone during the first 3 h, but a twofold increase was apparent after 6 h; levels remained elevated for up to 16 h of incubation. Immunoprecipitation of [35S]methionine-labeled rbENaC revealed a rise in protein levels of the alpha and beta subunits, but the protein level of the gamma subunit remained constant. In conclusion, our data suggest that in rabbit CNT and CCD the early increase in Na+ transport caused by aldosterone is due to the activation or insertion of existing Na+ channels into the apical membrane, and that the late response is mediated by increased synthesis of the alpha and beta rbENaC subunits.
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Affiliation(s)
- L Dijkink
- Department of Cell Physiology, Institute of Cellular Signalling, 162 Cell Physiology, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
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31
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Hoenderop JG, Vaandrager AB, Dijkink L, Smolenski A, Gambaryan S, Lohmann SM, de Jonge HR, Willems PH, Bindels RJ. Atrial natriuretic peptide-stimulated Ca2+ reabsorption in rabbit kidney requires membrane-targeted, cGMP-dependent protein kinase type II. Proc Natl Acad Sci U S A 1999; 96:6084-9. [PMID: 10339545 PMCID: PMC26839 DOI: 10.1073/pnas.96.11.6084] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Atrial natriuretic peptide (ANP) and nitric oxide (NO) are key regulators of ion and water transport in the kidney. Here, we report that these cGMP-elevating hormones stimulate Ca2+ reabsorption via a novel mechanism specifically involving type II cGMP-dependent protein kinase (cGK II). ANP and the NO donor, sodium nitroprusside (SNP), markedly increased Ca2+ uptake in freshly immunodissected rabbit connecting tubules (CNT) and cortical collecting ducts (CCD). Although readily increasing cGMP, ANP and SNP did not affect Ca2+ and Na+ reabsorption in primary cultures of these segments. Immunoblot analysis demonstrated that cGK II, and not cGK I, was present in freshly isolated CNT and CCD but underwent a complete down-regulation during the primary cell culture. However, upon adenoviral reexpression of cGK II in primary cultures, ANP, SNP, and 8-Br-cGMP readily increased Ca2+ reabsorption. In contrast, no cGMP-dependent effect on electrogenic Na+ transport was observed. The membrane localization of cGK II proved to be crucial for its action, because a nonmyristoylated cGK II mutant that was shown to be localized in the cytosol failed to mediate ANP-stimulated Ca2+ transport. The Ca2+-regulatory function of cGK II appeared isotype-specific because no cGMP-mediated increase in Ca2+ transport was observed after expression of the cytosolic cGK Ibeta or a membrane-bound cGK II/Ibeta chimer. These results demonstrate that ANP- and NO-stimulated Ca2+ reabsorption requires membrane-targeted cGK II.
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Affiliation(s)
- J G Hoenderop
- Department of Biochemistry, Institute of Cellular Signaling University of Nijmegen, P.O. Box 9101, NL-6500 HB Nijmegen, The Netherlands.
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32
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Hoenderop JG, van der Kemp AW, Hartog A, van de Graaf SF, van Os CH, Willems PH, Bindels RJ. Molecular identification of the apical Ca2+ channel in 1, 25-dihydroxyvitamin D3-responsive epithelia. J Biol Chem 1999; 274:8375-8. [PMID: 10085067 DOI: 10.1074/jbc.274.13.8375] [Citation(s) in RCA: 419] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In mammals, the extracellular calcium concentration is maintained within a narrow range despite large variations in daily dietary input and body demand. The small intestine and kidney constitute the influx pathways into the extracellular Ca2+ pool and, therefore, play a primary role in Ca2+ homeostasis. We identified an apical Ca2+ influx channel, which is expressed in proximal small intestine, the distal part of the nephron and placenta. This novel epithelial Ca2+ channel (ECaC) of 730 amino acids contains six putative membrane-spanning domains with an additional hydrophobic stretch predicted to be the pore region. ECaC resembles the recently cloned capsaicin receptor and the transient receptor potential-related ion channels with respect to its predicted topology but shares less than 30% sequence homology with these channels. In kidney, ECaC is abundantly present in the apical membrane of Ca2+ transporting cells and colocalizes with 1,25-dihydroxyvitamin D3-dependent calbindin-D28K. ECaC expression in Xenopus oocytes confers Ca2+ influx with properties identical to those observed in distal renal cells. Thus, ECaC has the expected properties for being the gatekeeper of 1,25-dihydroxyvitamin D3-dependent active transepithelial Ca2+ transport.
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Affiliation(s)
- J G Hoenderop
- Department of Cell Physiology, Institute of Cellular Signaling, University of Nijmegen, P. O. Box 9101, 6500 HB Nijmegen, The Netherlands
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33
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Pradervand S, Barker PM, Wang Q, Ernst SA, Beermann F, Grubb BR, Burnier M, Schmidt A, Bindels RJ, Gatzy JT, Rossier BC, Hummler E. Salt restriction induces pseudohypoaldosteronism type 1 in mice expressing low levels of the beta-subunit of the amiloride-sensitive epithelial sodium channel. Proc Natl Acad Sci U S A 1999; 96:1732-7. [PMID: 9990093 PMCID: PMC15577 DOI: 10.1073/pnas.96.4.1732] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The amiloride-sensitive epithelial sodium channel (ENaC) is a heteromultimer of three homologous subunits (alpha-, beta-, and gamma-subunits). To study the role of the beta-subunit in vivo, we analyzed mice in which the betaENaC gene locus was disrupted. These mice showed low levels of betaENaC mRNA expression in kidney (approximately 1%), lung (approximately 1%), and colon (approximately 4%). In homozygous mutant betaENaC mice, no betaENaC protein could be detected with immunofluorescent staining. At birth, there was a small delay in lung-liquid clearance that paralleled diminished amiloride-sensitive Na+ absorption in tracheal explants. With normal salt intake, these mice showed a normal growth rate. However, in vivo, adult betaENaC m/m mice exhibited a significantly reduced ENaC activity in colon and elevated plasma aldosterone levels, suggesting hypovolemia and pseudohypoaldosteronism type 1. This phenotype was clinically silent, as betaENaC m/m mice showed no weight loss, normal plasma Na+ and K+ concentrations, normal blood pressure, and a compensated metabolic acidosis. On low-salt diets, betaENaC-mutant mice developed clinical symptoms of an acute pseudohypoaldosteronism type 1 (weight loss, hyperkalemia, and decreased blood pressure), indicating that betaENaC is required for Na+ conservation during salt deprivation.
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Affiliation(s)
- S Pradervand
- Institut de Pharmacologie et de Toxicologie, Université de Lausanne, Rue du Bugnon 27, 1005 Lausanne, Switzerland
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Hoenderop JG, De Pont JJ, Bindels RJ, Willems PH. Hormone-stimulated Ca2+ reabsorption in rabbit kidney cortical collecting system is cAMP-independent and involves a phorbol ester-insensitive PKC isotype. Kidney Int 1999; 55:225-33. [PMID: 9893131 DOI: 10.1046/j.1523-1755.1999.00228.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Hormones such as parathyroid hormone (PTH), arginine vasopressin (AVP), and prostaglandin E2 (PGE2) are generally believed to act through cAMP to stimulate active Ca2+ reabsorption in the distal part of the nephron. METHODS This study investigates the relationship between intracellular cAMP levels and the rate of Ca2+ reabsorption in immunodissected rabbit connecting and cortical collecting tubules cultured to confluence on permeable supports. RESULTS Basolateral PTH, AVP, and PGE2 and apical adenosine dose dependently increased Ca2+ reabsorption from 48 to 110 nmol. hr-1. cm-2. Measurement of intracellular cAMP levels revealed that in the case of PTH and AVP, the dose-response curve for the increase in cAMP virtually matched that for transcellular Ca2+ transport. By contrast, with PGE2, this curve was shifted two decades to the right, whereas in the case of adenosine, no increase in cAMP was observed. The results with the latter two hormones disagree with the classic concept that Ca2+ reabsorption is stimulated via a cAMP-dependent mechanism. Furthermore, the potent adenylyl cyclase inhibitor 2', 5'-dideoxyadenosine (DDA; 100 micrometers) suppressed the PTH- and AVP-induced increase in cAMP completely without affecting Ca2+ reabsorption. Similarly, concentrations of PGE2, which maximally stimulated Ca2+ reabsorption without increasing cAMP, were not inhibited by DDA. The specific protein kinase C (PKC) inhibitor chelerythrine (5 micrometers) inhibited PTH-, AVP-, PGE2-, and adenosine-stimulated Ca2+ reabsorption by 77%, 67%, 79%, and 100%, respectively. Down-regulation of phorbol ester-sensitive PKC isotypes by prolonged (120 hr) treatment with 0.1 micrometers 12-O-tetradecanoylphorbol 13-acetate did not interfere with the inhibitory action of chelerythrine on hormone-stimulated Ca2+ transport. CONCLUSION PTH, AVP, PGE2, and adenosine stimulate Ca2+ reabsorption via a pathway that is independent of cAMP and that involves a phorbol ester-insensitive PKC isotype.
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Affiliation(s)
- J G Hoenderop
- Departments of Biochemistry and Cell Physiology, University of Nijmegen, Institute of Cellular Signalling, Nijmegen, The Netherlands.
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Abstract
To elucidate potential mechanisms of ischemic renal injury, investigators often use drugs that interfere with specific pathological pathways and study their protective efficacy in in vitro models of ischemia, such as isolated renal proximal tubules subjected to hypoxia. However, the protective effects of certain drugs may depend on non-specific membrane-stabilizing properties. We have studied the effects of several drugs on membrane integrity using osmotic lysis of erythrocytes as a model system. Freshly isolated rabbit erythrocytes were subjected to a hypotonic shock, and the protective effects of various calcium channel blockers, phospholipase inhibitors, free fatty acids, the NO-synthase inhibitor L-NAME, the amino acid glycine and its receptor-analogue strychnine, and two chloride channel blockers were examined. Most agents protected erythrocytes against hypotonic hemolysis when added to the medium in the same concentration range as used in suspensions of hypoxic proximal tubules. Only the protective agents that proposedly act via a blockade of chloride influx (glycine, strychnine and the chloride channel blockers), did not attenuate hypotonic hemolysis. The erythrocyte hemolysis assay may provide an easy and rapid method to screen for non-specific membrane-stabilizing effects of potentially cytoprotective agents.
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Affiliation(s)
- S M Peters
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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36
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Hoenderop JG, Hartog A, Willems PH, Bindels RJ. Adenosine-stimulated Ca2+ reabsorption is mediated by apical A1 receptors in rabbit cortical collecting system. Am J Physiol 1998; 274:F736-43. [PMID: 9575898 DOI: 10.1152/ajprenal.1998.274.4.f736] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Confluent monolayers of immunodissected rabbit connecting tubule and cortical collecting duct cells, cultured on permeable supports, were used to study the effect of adenosine on net apical-to-basolateral Ca2+ transport. Apical, but not basolateral, adenosine increased this transport dose dependently from 48 +/- 3 to 110 +/- 4 nmol.h-1.cm-2. Although a concomitant increase in cAMP formation suggested the involvement of an A2 receptor, the A2 agonist CGS-21680 did not stimulate Ca2+ transport, while readily increasing cAMP. By contrast, the A1 agonist N6-cyclopentyladenosine (CPA) maximally stimulated Ca2+ transport without significantly affecting cAMP. Adenosine-stimulated transport was effectively inhibited by the A1 antagonist 1,3-dipropyl-8-cyclopenthylxanthine but not the A2 antagonist 3,7-dimethyl-1-propargylxanthine, providing additional evidence for the involvement of an A1 receptor. Both abolishment of the adenosine-induced transient increase in intracellular Ca2+ concentration by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid and downregulation of protein kinase C (PKC) by prolonged phorbol ester treatment were without effect on adenosine-stimulated Ca2+ transport. The data presented suggest that adenosine interacts with an apical A1 receptor to stimulate Ca2+ transport via a hitherto unknown pathway that does not involve cAMP formation, PKC activation, and/or Ca2+ mobilization.
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Affiliation(s)
- J G Hoenderop
- Department of Biochemistry, University of Nijmegen, The Netherlands
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37
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Peters SM, Rauen U, Tijsen MJ, Bindels RJ, van Os CH, de Groot H, Wetzels JF. Cold preservation of isolated rabbit proximal tubules induces radical-mediated cell injury. Transplantation 1998; 65:625-32. [PMID: 9521195 DOI: 10.1097/00007890-199803150-00005] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND Reactive oxygen species (ROS) are involved in reperfusion injury after preservation. Recent studies in isolated endothelial cells and hepatocytes suggested the occurrence of ROS-mediated injury during the period of cold incubation. In the present study, formation of ROS and subsequent cell injury were studied in freshly isolated rabbit proximal tubules (PTs). METHODS PTs were incubated in University of Wisconsin (UW) solution, Euro-Collins solution, or a modified Krebs-Henseleit buffer under aerobic conditions for up to 94 hr at 4 degrees C. ROS formation and cell death were assessed as lipid peroxidation (formation of thiobarbituric acid-reactive substances [TBARS]) and release of lactate dehydrogenase, respectively. The involvement of ROS was further investigated in UW solution using compounds that might interfere with ROS formation. In addition, tubules were studied under anaerobic conditions (gassing with 95% N2/5% CO2). RESULTS Cold preservation of rabbit PTs in any of the solutions under aerobic conditions caused progressive lipid peroxidation and concomitant cell injury. Addition to UW solution of inhibitors of ROS formation, in particular 2,2'-dipyridyl, or removal of oxygen by gassing with 95% N2/5% CO2, prevented lipid peroxidation and protected rabbit PTs against cold injury. Both the nitric oxide (NO) synthase inhibitor L-NAME and dexamethasone, which blocks the inducible NO synthase, were ineffective. The cytoprotectant glycine affected neither TBARS formation nor lactate dehydrogenase release. CONCLUSIONS Cold preservation of renal PTs under aerobic conditions caused cell injury even in the specially designed preservation solution UW. Cell injury is caused by iron-dependent, NO synthase-independent ROS formation.
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Affiliation(s)
- S M Peters
- Department of Internal Medicine, University Hospital Nijmegen, The Netherlands
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Abstract
Renal ischemia results in adenosine triphosphate (ATP) depletion, particularly in cells of the proximal tubule (PT), which rely heavily on oxidative phosphorylation for energy supply. Lack of ATP leads to a disturbance in intracellular homeostasis of Na+, K+ and Cl-. Also, cytosolic Ca2+ levels in renal PTs may increase during hypoxia [1], presumably by a combination of impaired extrusion and enhanced influx [2]. However, Ca2+ influx was previously measured using radiolabeled Ca2+ and at varying partial oxygen tension [2]. We have now used to Mn2(+)-induced quenching of fura-2 fluorescence to study Ca2+ influx in individual rat PTs during normoxic and hypoxic superfusion. Normoxic Ca2+ influx was indeed reflected by the Mn2+ quenching of fura-2 fluorescence and this influx could be inhibited by the calcium entry blocker methoxyverapamil (D600; inhibition 50 +/- 2% and 35 +/- 3% for 10 and 100 mumol, respectively). La3+ completely blocked normoxic Ca2+ influx. Hypoxic superfusion or rat PTs did not induce an increase in Ca2+ influx, but reduced this influx to 79 +/- 3% of the normoxic control. We hypothesize that reducing Ca2+ influx during hypoxia provides the cell with a means to prevent cellular Ca2+ overload during ATP-depletion, where Ca2+ extrusion is limited.
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Affiliation(s)
- S M Peters
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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Bouritius H, Oprins JC, Bindels RJ, Hartog A, Groot JA. Neuropeptide Y inhibits ion secretion in intestinal epithelium by reducing chloride and potassium conductance. Pflugers Arch 1998; 435:219-26. [PMID: 9382934 DOI: 10.1007/s004240050504] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Neuropeptide Y (NPY) is probably the most abundant neuropeptide, with a plethora of central as well as peripheral effects, including its proabsorptive action in the gastro-intestinal tract. The effects of NPY on electrical parameters related to three different pathways stimulating ion secretion were investigated using the human intestinal cell line HT29cl.19A. Transepithelial potential and resistance were measured with the preparation maintained in a horizontal Ussing chamber, allowing simultaneous measurement of the membrane potential and determination of the fractional resistance of the apical cell membrane. It was found that application of NPY, after the adenylyl-cyclase-activating drug forskolin, resulted in complete inhibition of forskolin-induced effects within approximately 20 min. The secretion stimulated by adenosine appeared to be insensitive to NPY. The acetylcholine analogue carbachol stimulates ion secretion by increasing intracellular free calcium concentrations ([Ca2+]i) which activates the basolateral potassium (K+) conductance. NPY caused 50% inhibition of the effect of carbachol. Measurements of [Ca2+]i showed that NPY inhibited the carbachol-induced rise in [Ca2+]i, which correlates with the reduced activation of basolateral K+ channels. From this study we conclude that NPY inhibits cAMP-stimulated as well as Ca2+-stimulated secretion via a reduction in the apical Cl- and basolateral K+ conductance. This double effect makes NPY an effective proabsorptive peptide.
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Affiliation(s)
- H Bouritius
- Institute of Neurobiology, Biological Faculty, University of Amsterdam, Graduate School Neurosciences Amsterdam, Kruislaan 320, NL-1098 SM Amsterdam, The Netherlands
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Tijsen MJ, Peters SM, Bindels RJ, van Os CH, Wetzels JF. Glycine protection against hypoxic injury in isolated rat proximal tubules: the role of proteases. Nephrol Dial Transplant 1997; 12:2549-56. [PMID: 9430850 DOI: 10.1093/ndt/12.12.2549] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND Isolated rat proximal tubules are frequently used as a model to study hypoxic injury. Glycine is a very effective protective agent against hypoxia-induced cell injury in this model. The mechanisms involved in hypoxic renal injury and glycine protection are still debated. We have focused on the role of proteolytic enzymes. METHODS Isolated rat proximal tubules in suspension were gassed with either 95%O2/5%CO2 or 95%N2/5%CO2 to create normoxic or hypoxic conditions. Cell injury was assessed by the release of LDH. Activity of proteolytic enzymes was measured by quantifying the release of fluorescent 7-amino-4-methylcoumarin from specific substrates, which were added to tubules in suspension or to cytosolic fractions of permeabilized tubules. RESULTS Fifteen minutes of hypoxia caused cell injury, which was completely prevented by glycine. Activities of serine-, aspartate-, and the calcium-dependent cysteine protease calpain were increased in these hypoxic tubules in suspension, but only calpain activity was attenuated by glycine. Cytosolic fractions obtained by digitonin-permeabilization of hypoxic (15 min) tubules showed increased proteolytic activity of all measured classes of proteases and glycine prevented these increases. In measurements performed at an earlier time point (7.5 min) neither changes in calpain activity nor effects of glycine were detected. Calpain activity was not inhibited directly by glycine. CONCLUSIONS Hypoxia increases the activity of several classes of proteases. The effects of glycine on protease activation are equivocal, and may merely reflect the potential of glycine to prevent hypoxia-induced lethal membrane injury.
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Affiliation(s)
- M J Tijsen
- Department of Medicine, University of Nijmegen, The Netherlands
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41
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Mulders SM, Rijss JP, Hartog A, Bindels RJ, van Os CH, Deen PM. Importance of the mercury-sensitive cysteine on function and routing of AQP1 and AQP2 in oocytes. Am J Physiol 1997; 273:F451-6. [PMID: 9321919 DOI: 10.1152/ajprenal.1997.273.3.f451] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To discriminate between water transport of of aquaporin-2 (AQP2) mutants in nephrogenic diabetes insipidus and that of an AQP2 molecule used to drag them to the oolemma, we investigated the mercury sensitivity of wild-type and AQP2 C181S proteins in oocytes. Incubation with HgCl2 inhibited the osmotic water permeability (Pf) of human (h) AQP2 by 40%, whereas inhibition of hAQP1 was 75%. Oocytes expressing hAQP1 C189S revealed a Pf comparable to wild-type hAQP1, but mercury sensitivity was lost. In contrast, no increase in Pf was obtained when hAQP2 C181S was expressed. Also, expression of rat AQP2 C181A and C181S mutants did not increase the Pf, which contrasts with published observations. Immunocytochemistry and immunoblotting revealed that only AQP1, AQP1 C189S, and AQP2 were targeted to the plasma membrane and that AQP2 mutant proteins are retarded in the endoplasmic reticulum. In conclusion, water transport through AQP2 is less sensitive to mercury inhibition than through AQP1. Furthermore, substitution of the mercury-sensitive cysteine for a serine results in an impaired routing of human and rat AQP2. Similar mutations have no effect on AQP1 function, which is indicative of structural differences between AQP1 and AQP2.
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Affiliation(s)
- S M Mulders
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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Raber G, Willems PH, Lang F, Nitschke R, van Os CH, Bindels RJ. Co-ordinated control of apical calcium influx and basolateral calcium efflux in rabbit cortical collecting system. Cell Calcium 1997; 22:157-66. [PMID: 9330786 DOI: 10.1016/s0143-4160(97)90009-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Transcellular Ca2+ transport in the distal nephron involves passive Ca2+ influx at the apical membrane, diffusion through the cytosol and active extrusion across the opposing basolateral membrane. The molecular identity of the apical Ca2+ entry step is still elusive, but its regulatory aspects have been analyzed in the present study. To this end, rabbit connecting and cortical collecting tubular cells were cultured on permeable and transparent supports and the apical Ca2+ influx was deduced from Mn2+ quenching of Ca2+ independent Fura-2 fluorescence, while the intracellular Ca2+ concentration ([Ca2+]i) was measured simultaneously. In parallel experiments, transcellular Ca2+ transport was determined isotopically as 45Ca2+ flux from the apical to basolateral compartment. Decreasing the apical pH from 7.4 to 5.9 inhibited transcellular Ca2+ transport by 53 +/- 1%, whereas apical Ca2+ influx was reduced by 39 +/- 7% and [Ca2+]i decreased by 18 +/- 3%. Reversal of the Na+/Ca2+ exchanger by iso-osmotic replacement of Na+ by N-methyl-D-glucamine in the basolateral compartment resulted in 50 +/- 5% inhibition of Ca2+ transport, 46 +/- 3% reduction of apical Ca2+ influx and 60 +/- 3% increase in [Ca2+]i. In the absence of basolateral Ca2+, however, this manoeuvre decreased [Ca2+]i by 21 +/- 8%, while Ca2+ transport and apical Ca2+ influx were reduced by the same magnitude as in the presence of Ca2+, that is by 53 +/- 6% and 45 +/- 4%, respectively. Stimulation of adenylyl cyclase with forskolin (10(-5) M) increased transcellular Ca2+ transport by 108 +/- 40%, stimulated apical Ca2+ influx by 120 +/- 17% and increased [Ca2+]i by 110 +/- 2%. In conclusion, the apical Ca2+ influx is regulated by apical pH, intracellular cAMP and basolateral Na+/Ca2+ exchanger activity, and is coupled in an 1:1 fashion to the rate of transepithelial Ca2+ transport.
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Affiliation(s)
- G Raber
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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Deen PM, Nielsen S, Bindels RJ, van Os CH. Apical and basolateral expression of aquaporin-1 in transfected MDCK and LLC-PK cells and functional evaluation of their transcellular osmotic water permeabilities. Pflugers Arch 1997; 433:780-7. [PMID: 9049170 DOI: 10.1007/s004240050345] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Aquaporin-1 is present in the apical and basolateral membranes in proximal tubules and descending limbs of Henlé's loop. In order ot be able to study the routing of Aquaporin-1 and the regulation of Aquaporin-1-mediated transcellular water flow, we stably transfected LLC-PK1 and MDCK-HRS cell lines with an Aquaporin-1 expression construct. LLC-PK1 clone 7 and MDCK clone K integrated two and one copies, respectively, which was reflected in the amount of Aquaporin-1 mRNA expressed in both clones. The Aquaporin-1 protein levels, however, were similar. In both clones, immuno-electronmicroscopy showed extensive labelling of Aquaporin-1 on the basolateral plasma membrane, endosomal vesicles and the apical plasma membrane, including the microvilli. To measure transcellular water permeation, a simple method was applied using phenol-red as a cell-impermeant marker of concentration. In contrast to the native cell lines, both clones revealed a high transcellular osmotic water permeability, which could not be influenced by forskolin add/3-isobutyl-1-methylxanthine (IBMX) or the phorbol ester 12-O-tetradecanoyl 13-acetate (TPA). After glutaraldehyde fixation, it was inhibitable by HgCl2. These results indicate that targeting of Aquaporin-1 to the apical and basolateral plasma membrane is independent of cell type and show for the first time that water flow through a cultured epithelium can be blocked by mercurial compounds.
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Affiliation(s)
- P M Deen
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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van Kuijck MA, Kool M, Merkx GF, Geurts van Kessel A, Bindels RJ, Deen PM, van Os CH. Assignment of the canalicular multispecific organic anion transporter gene (CMOAT) to human chromosome 10q24 and mouse chromosome 19D2 by fluorescent in situ hybridization. Cytogenet Cell Genet 1997; 77:285-7. [PMID: 9284939 DOI: 10.1159/000134599] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Rabbit epithelial basolateral chloride conductance regulator (EBCR) and rat canalicular multispecific organic anion transporter (Cmoat) are found to be homologues based on protein sequence comparison and Northern blot analysis. EBCRis, therefore, renamed as rabbit Cmoat. The gene encoding CMOAT, a transporter possibly involved in Dubin-Johnson syndrome in humans, is mapped on human chromosome 10q24 and mouse chromosome 19D2.
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Affiliation(s)
- M A van Kuijck
- Department of Cell Physiology, University of Nijmengen, The Netherlands.
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van Baal J, de Jong MD, Zijlstra FJ, Willems PH, Bindels RJ. Endogenously produced prostanoids stimulate calcium reabsorption in the rabbit cortical collecting system. J Physiol 1996; 497 ( Pt 1):229-39. [PMID: 8951725 PMCID: PMC1160926 DOI: 10.1113/jphysiol.1996.sp021763] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
1. The influence of endogenously produced prostanoids on active transepithelial Ca2+ transport and cAMP formation was investigated in immunodissected rabbit kidney connecting and cortical collecting tubule cells grown to confluency on permeable supports. 2. The cyclo-oxygenase inhibitor indomethacin dose-dependently (IC50 = 18 nM) reduced the net apical-to-basolateral Ca2+ transport by 57%. Inhibition was reversed in medium obtained from monolayers incubated in the absence of indomethacin. 3. HPLC analysis following incubation with 14C-labelled arachidonic acid revealed the presence of a wide variety of radiolabelled prostanoids in both the apical and basolateral media. These findings are compatible with the endogenous production and subsequent release of stimulatory prostanoids. 4. The inhibitory action of indomethacin was reversed by the addition of the prostanoids PGE1, PGE2 and PGA2, but not PGD2, PGF2 alpha, the stable PGI2 analogue cicaprost or the thromboxane A2 mimetic U-46619. PGE2 stimulated transepithelial Ca2+ transport dose dependently (EC50 = 3 nM), irrespective of the compartment of which it was added. The stimulatory effect of PGE2 was paralleled by increased cAMP formation, suggesting the apical and basolateral presence of stimulatory prostanoid receptors EP2 and/or EP4. 5. Sulprostone, an analogue selective for EP1 and EP3 receptors, inhibited transepithelial Ca2+ transport in indomethacin-treated monolayers only when applied basolaterally, suggesting the exclusive presence of inhibitory EP receptors on the basolateral membrane. 6. The percentage by which parathyroid hormone and arginine vasopressin increased both transepithelial Ca2+ transport and cAMP formation was dramatically increased in indomethacin-inhibited cells as compared with control cells, demonstrating that indomethacin unmasks the actions of these hormones to their full extent.
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Affiliation(s)
- J van Baal
- Department of Cell Physiology, University of Nijmegen, The Netherlands.
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46
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Peters SM, Tijsen MJ, Bindels RJ, Van Os CH, Wetzels JF. Rise in cytosolic Ca2+ and collapse of mitochondrial potential in anoxic, but not hypoxic, rat proximal tubules. J Am Soc Nephrol 1996; 7:2348-56. [PMID: 8959624 DOI: 10.1681/asn.v7112348] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
It has been suggested that ischemic renal proximal tubular cell injury is mediated by an increase in cytosolic calcium concentrations ((Ca2+)i). However, measurements of (Ca2+)i in rat or rabbit proximal tubules exposed to hypoxia or anoxia have yielded ambiguous results. This study explored the possibility that the severity of oxygen deprivation and the energy state of the mitochondria are important determinants of (Ca2+)i. To this end, (Ca2+)i (measured with fura-2) and the mitochondrial membrane potential (measured with rhodamine 123) were studied simultaneously in individual rat proximal tubules in hypoxic and anoxic conditions. (Ca2+)i did not change during hypoxia, but increased rapidly during anoxia. Increases in (Ca2+)i were only observed in parallel with a decrease of rhodamine 123 fluorescence, which indicates a collapse of the mitochondrial membrane potential. The increase in (Ca2+)i during anoxia was prevented by incubating the tubules in a low Ca2+ medium, which did not interfere with the collapse of the mitochondrial membrane potential. Both hypoxic and anoxic incubation led to cell death, as assessed by the fluorescent dye propidium iodide. These results clearly demonstrate that the level of oxygen deprivation is critical in determining changes in (Ca2+)i. Because cell damage occurred in both hypoxic and anoxic conditions. It was concluded that an increase in (Ca2+)i is not a necessary prerequisite for the development of ischemic cell injury.
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Affiliation(s)
- S M Peters
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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Abstract
Surface and crypt cells of rabbit distal colon were separately isolated, and amiloride-sensitive 22Na+ uptake could only be demonstrated in a crude membrane fraction derived from surface cells. For purification of apical membranes of surface and crypt cells (H(+)-K+)-ATPase and alkaline phosphatase were used as putative apical membrane markers. Apical membranes of surface cells were isolated after mild homogenization, low speed centrifugation, and subsequent fractionation on a Percoll density gradient. Apical membranes of crypt cells were collected after more vigorous homogenization, followed by high speed centrifugation, and fractionation on a Percoll gradient. In surface and crypt cells, (H(+)-K+)-ATPase and alkaline phosphatase activity accumulated in a low and a high density Percoll band. Further fractionation of the low density Percoll band from crypt cells on a discontinuous sucrose gradient yielded a vesicle fraction with 7- to 10-fold enrichment in (H(+)-K+)-ATPase activities. To demonstrate the usefulness of the isolated fractions in studying transport mechanisms, vesicle volume was determined and planar lipid bilayer studies were performed. In the latter studies, a 83-pS 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS)-sensitive Cl(-)-channel, resembling the outward rectifying intermediate conductance (ORIC) Cl(-)-channel of secretory epithelia, was encountered most frequently. This channel was present in fractions of surface and crypt cells.
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Affiliation(s)
- S L Abrahamse
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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Van Baal J, Yu A, Hartog A, Fransen JA, Willems PH, Lytton J, Bindels RJ. Localization and regulation by vitamin D of calcium transport proteins in rabbit cortical collecting system. Am J Physiol 1996; 271:F985-93. [PMID: 8945992 DOI: 10.1152/ajprenal.1996.271.5.f985] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3]-induced expression of Na+/Ca2+ exchanger, Ca(2+)-adenosinetriphosphatase (Ca(2+)-ATPase), and calbindin-D28k was investigated in the rabbit distal nephron. Immunocytochemical studies in rabbit kidney sections revealed colocalization of the three Ca2+ transport proteins in the majority of cells in the distal nephron, including connecting tubules and cortical collecting ducts. Subsequently, rabbit connecting and cortical collecting tubule cells were immunodissected and cultured on permeable supports. Immunocytochemical analysis of the cultured cells by confocal microscopy revealed that Na+/Ca2+ exchanger and Ca(2+)-ATPase were present at the basolateral membrane, whereas calbindin-D28k was evenly distributed throughout the cytosol. Concomitant with an increase in Ca2+ transport, 1,25(OH)2D3 increased calbindin-D28k protein and RNA content two- to threefold, as determined by Northern and Western blotting. By contrast, neither Na+/Ca2+ exchanger nor Ca(2+)-ATPase RNA or protein content was noticeably altered. Our findings suggest that 1,25(OH)2D3 stimulation of transcellular Ca2+ transport in primary cultures of rabbit cortical collecting system cells involves an increase in the gene expression of calbindin-D28k but not of Na+/Ca2+ exchanger and Ca(2+)-ATPase.
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Affiliation(s)
- J Van Baal
- Department of Cell Physiology, University of Nijmegen, The Netherlands
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van Baal J, Raber G, de Slegte J, Pieters R, Bindels RJ, Willems PH. Vasopressin-stimulated Ca2+ reabsorption in rabbit cortical collecting system: effects on cAMP and cytosolic Ca2+. Pflugers Arch 1996; 433:109-15. [PMID: 9019710 DOI: 10.1007/s004240050255] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The effect of arginine vasopressin (AVP) on transepithelial Ca2+ transport in primary cultures of rabbit cortical collecting system cells was examined. Addition of AVP to the basolateral side of the monolayer dose-dependently (EC50 = 0.7 nM) increased active Ca2+ reabsorption from a basal value of 85 +/- 2 nmol.h-1.cm-2 to a maximum value of 124 +/- 3 nmol.h-1.cm-2. This was paralleled by a dose-dependent (EC50 = 1.1 nM) increase in cellular adenosine 3', 5'-cyclic monophosphate (cAMP) content. Both effects of AVP were mimicked by the V2 agonist deamino-Cys,D-Arg8-vasopressin (dDAVP) and forskolin. Addition of either AVP or dDAVP to the basolateral side evoked a sustained increase in cytosolic free Ca2+ concentration, which resulted from both Ca2+ entry and release from internal stores. Only the effect on Ca2+ entry was mimicked by forskolin, demonstrating that cAMP acts by activating a Ca2+ influx pathway. The present findings demonstrate that AVP stimulates transcellular Ca2+ transport in the cortical collecting system through activation of basolateral V2 receptors coupled to adenylyl cyclase to increase the cellular cAMP content.
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Affiliation(s)
- J van Baal
- Department of Cell Physiology, University of Nijmegen, PO Box 9101, NL-6500 HB Nijmegen, The Netherlands
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Bindels RJ, Engbersen AM, Hartog A, Blazer-Yost BL. Aldosterone-induced proteins in primary cultures of rabbit renal cortical collecting system. Biochim Biophys Acta 1996; 1284:63-8. [PMID: 8865816 DOI: 10.1016/0005-2736(96)00113-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Primary cultures of immunodissected cells from rabbit kidney connecting tubule and cortical collecting duct were used to study aldosterone's action on transcellular Na+ flux. Incubation with 10(-7) M aldosterone stimulated transcellular Na+ transport which was detected as an increase in benzamil-sensitive short-circuit current. The stimulatory response was consistently noted after 2 h of incubation and stabilized after 6 h. 2D-PAGE was used to identify proteins which were induced concurrently with the increase in transcellular Na+ flux after an aldosterone incubation of 15 h. Three aldosterone-induced proteins (AIPs; M(r) = 100, 70-77 and 46-50 kDa) were found in the membrane and microsomal fractions. Two of these appeared to have more than one isoform. A single heterogeneous AIP (M(r) = 77 kDa) was detected in the soluble fraction.
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Affiliation(s)
- R J Bindels
- Department of Cell Physiology (162), University of Nijmegen, The Netherlands.
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