Quantification of TGF-beta1 mRNA along rat nephron in obstructive nephropathy

Unilateral ureteral obstruction (UUO) leads to interstitial fibrosis of the obstructed kidney, and transforming growth factor-beta1 (TGF-beta1) is thought to play an important role in this process. Although increased TGF-beta1 mRNA expression in the obstructed kidney has been demonstrated, the source of the increased TGF-beta1 remains to be elucidated. To determine the precise localization of TGF-beta1 in the obstructed kidney, we examined TGF-beta1 mRNA expression using in situ hybridization and competitive RT-PCR in rats with UUO. In situ hybridization demonstrated that TGF-beta1 mRNA expression was preferentially increased in tubular epithelial cells and to a lesser degree in infiltrating macrophages in obstructed kidneys. Quantitative analysis using competitive RT-PCR in microdissected nephron segments revealed that levels of TGF-beta1 mRNA in obstructed kidneys relative to control kidneys increased significantly in proximal tubules, thick ascending limbs of Henle, and distal convoluted tubules, whereas those in glomeruli and collecting ducts did not change significantly. Of the tubular segments, the proximal tubules appeared to predominantly contribute to increased TGF-beta1 mRNA. Our findings suggest that renal tubules, particularly proximal tubules, are the main contributors to increased TGF-beta1 mRNA expression in obstructed kidneys and to the subsequent interstitial fibrosis.

Effect of protamine on cation-selective permeability in hamster medullary thick ascending limb of Henle's loop

To estimate the contribution of the paracellular shunt pathway to cation-selective permeability in the hamster medullary thick ascending limb of Henle's loop, we observed the effect of protamine, a selective blocker of paracellular conductance, on salt-diffusion voltage (dVT) in the isolated nephron segment perfused in vitro. When 300 microg/ml protamine was added to the lumen, the lumen-positive dVT generated upon reduction of the lumen NaCl concentration was decreased from 5.1 +/- 0.9 to 0.8 +/- 0.8 mV and the calculated Na+/Cl- permeability ratio was decreased from 1.40 +/- 0.14 to 0.86 +/- 0.08. Although the effect of protamine persisted after removal of the agent from the lumen, addition of 30 U/ml heparin, which neutralizes protamine, returned the dVT toward the control level. This effect was almost the same when the orientation of the imposed NaCl gradient was reversed. Protamine exhibited a similar effect on dVT in the presence of ouabain added to the bath. Protamine was without effect from the bath. Protamine did not affect the basel VT perfused with the control solution. Increased VT by decreasing perfusion pressure was inhibited by adding protamine from the lumen. These observations suggest that the paracellular pathway contributes to the cation selectivity of the medullary thick ascending limb. The cation selectivity of the paracellular shunt pathway may mainly account for the changes in VT which are either dependent on the luminal flow rate or transmural NaCl concentration gradient, while it may not contribute to the basal level of VT.

[Peer review in toxicologic histopathology: its necessity, type and procedure]

A histopathology peer review already has become an integral part of industrial toxicologic pathology in the USA and Europe. Nevertheless, the review is unfamiliar to toxicologic pathologists in Japan. This report provides detailed information on convenient, useful procedures for peer review in toxicologic histopathology and describes its necessity and type. Histopathology peer review is either informal or formal. Formal review means that the target organs to be re-estimated and the reviewing pathologist's name are stated somewhere in a protocol or study report. The resolution of all diagnostic discrepancies between studies and reviewing pathologists must be clarified, and the review records need to be preserved. No audit trials need to be kept for informal peer review. Based on the purpose of the review, histopathology peer reviews may be classified into 3 major types: "complete", "problem-solving", and a "quality-monitoring" reviews. For a "Complete" review, all histopathologic findings crucial to the conclusion of the study are re-examined. A "problem-solving" review serves to re-evaluate anomalous findings. A "quality-monitoring" review is a periodical monitor of the quality of histopathologic diagnoses at pathology laboratories, particularly in toxicology contract research organizations. The procedures for histopathology peer review consist of 5 stages. At the first stage, the target organs to be reviewed are selected from the draft summary tables of the original findings diagnosed by the study pathologist, and the reviewing pathologist evaluates all selected organs. At the second stage, the study pathologist re-examines all the findings with diagnoses not accepted by the reviewing pathologist and re-considers the appropriateness of these original diagnoses. At the third stage, the study pathologist and the reviewing pathologists discuss all diagnostic differences until they reach a consensus opinion. At the fourth stage, the whole process (stage 1 to 3) of peer review of all target organs is tabulated, including the study pathologist's and reviewing pathologist's diagnoses, the study pathologist's opinions, and consensus diagnoses. At the fifth stage, Peer Review Certification is issued with the study pathologists' and reviewing pathologists' signatures. The reviewing pathologist must share the responsibility for the final diagnoses with the study pathologist. In order to gain greater credibility from regulatory agencies, a peer review performance is best made by an independent external pathologist.

On the mechanism of bicarbonate exit from renal proximal tubular cells

We compare here the results of electrophysiological measurements on proximal tubular cells performed on rat kidney in vivo and on isolated rabbit and rat tubules in vitro. Based on different effects of carbonic anhydrase inhibitors in the in vivo and in vitro preparation, we conclude that NaHCO3 cotransport across the basolateral cell membrane functions as Na(+)-CO3(2-)-HCO3- cotransport in vivo, but as Na(+)-HCO3(-)-HCO3- cotransport in the classical in vitro preparation. The former, but not the latter, transport mode is characterized by generation of local disequilibrium pH/CO3(2-) concentrations that oppose fluxes if membrane-bound carbonic anhydrase is inhibited. In support of this conclusion, we find that overall transport functions with a HCO3- to Na+ stoichiometry of 3:1 in vivo (since each transported CO3(2-) eventually generates 2 HCO3- ions), but 2:1 in vitro. This has been deduced from various measurements, among them super-Nernstian and reverse nernstian, potential responses to changing ion concentrations which are characteristic of obligatorily coupled cation-anion cotransporters, but are not known in classical electrochemistry. The different transport modes in vivo and in vitro suggest that isolated proximal tubules have functional deficits compared to proximal tubules in vivo.

Functional characterization of vasopressin V1 and V2 receptors in the rabbit renal cortical collecting duct

Recently we clarified the mechanism in which arginine-vasopressin (AVP) applied from the luminal side inhibits the basolateral Cl- conductance, which is stimulated by basolateral AVP. However, to prove that these vasopressin phenomena are expressed via receptor mediated actions, we examined the effect of specific V1 and V2 receptor antagonists, OPC-21268 and OPC-31260, respectively, on the electrical response to vasopressin in the rabbit CCD perfused in vitro. In the presence of the V2-antagonist, basolateral AVP caused only the activation of luminal Na+ conductance, indicating a V1 action. In the presence of the V1 antagonist, basolateral AVP caused the same biphasic responses in electrical parameters as cyclic AMP, representing a pure V2 action. On the other hand, a rise in cell Ca2+ in response to AVP was completely abolished in the presence of the V1-antagonist, but not by the V2-antagonist in the bath. These data confirm our earlier findings that rabbit CCD possesses both V1 and V2 receptors in the basolateral membrane. We conclude that electrical responses to AVP in the rabbit CCD are a complex of V1 and V2 receptor-mediated actions.

Localization of transforming growth factor-beta and latent transforming growth factor-beta binding protein in rat kidney

TGF-beta plays an important role in maintaining the renal histological structure, and glomerular and tubular function. TGF-beta is usually secreted in a biologically inactive or latent form with high molecular weight by normal cells. The latent form of TGF-beta is composed of three distinct components: (a) mature TGF-beta (b) TGF-beta latency associated peptide (LAP) (c) latent TGF-beta binding protein (LTBP). LTBP plays a central role in the assembly, secretion and activation of TGF-beta 1. Most cells secrete a large latent TGF-beta with LTBP, while the other cells secrete a small latent TGF-beta without LTBP. However, the precise localization of TGF-beta and LTBP in the kidney is still not known. In the present study, we used the reverse transcription in combination with polymerase chain reaction (RT-PCR) to investigate the precise localization of TGF-beta 1 and LTBP in the microdissected glomeruli, renal tubules and arterioles. Our findings showed that TGF-beta 1 mRNA was detected in all nephron segments, glomeruli, and arterioles. On the other hand, LTBP mRNA was present in the glomeruli and arterioles, while it was absent in every segment of the renal tubules. Moreover, the immunohistochemical study of LTBP showed that the LTBP protein was localized on the glomeruli and arterioles but not on the renal tubules at the same localization as LTBP mRNA. These results indicate that the tubular epithelial cells secrete the small latent TGF-beta 1, while glomerular cells secrete the large latent TGF-beta 1, suggesting that they both have different structures and thus potentially different biological functions.

Pathology and incidence of amelanotic melanomas of the skin in F-344/N rats

A total of 121 spontaneous amelanotic melanomas of the skin were identified in 70 of 11,171 male and 51 of 10,927 female Fischer-344/N rats in 63 2-yr carcinogenicity studies conducted by the National Cancer Institute's Carcinogenicity Testing Program/National Toxicology Program. Amelanotic melanomas had characteristic anatomical locations and histologic features distinguishable from Schwann cell tumors. Of the 121 tumors, 84, 19, 10, and 8 cases occurred in the pinna, eyelid, scrotum, and perianal region (anus and tail), respectively. Amelanotic melanomas originated from the dermis and consisted of spindle cells arranged in an interlacing fascicular pattern often with a perivascular orientation; epithelioid cells were rarely seen. Only the tumors arising in the pinna metastasized to the lung and/or mandibular lymph nodes. The metastatic rate was 19% (16/84) of the tumors and was clearly increased with an increase in tumor size. Most metastasizing tumors had focal areas consisting of anaplastic spindle cells with an increased number of mitosis. The tumor cells stained positive for S-100 protein but negative for melanin. Ultrastructurally, the tumors were diagnosed as amelanotic melanomas based on the identification of numerous, intracytoplasmic premelanosomes without melanin formation in the tumor cells which were not enveloped by pericytoplasmic basal laminae. One localized amelanotic melanoma of the pinna was successfully transplanted to the subcutaneous tissue in the flank of 3 Fischer-344/N rats.

Electrophysiological study of luminal and basolateral vasopressin in rabbit cortical collecting duct

To clarify the mechanism of action of arginine vasopressin (AVP) on ionic conductances, electrophysiological technique was applied to the rabbit cortical collecting duct (CCD) perfused in vitro. When AVP (100 pM) was added to the bath, transepithelial voltage (VT), transepithelial resistance (RT), and fractional resistance of the apical membrane (fRA) of the principal cell displayed biphasic responses: initial increase in lumen-negative VT (phase I) was associated with decreases in RT and fRA, whereas secondary decrease in VT (phase II) was associated with increases in RT and fRA. In phase I, depolarization of the luminal membrane was observed due to stimulation of Na+ conductance in the luminal membrane. In phase II, mixed responses of both hyperpolarization of the luminal membrane, due to late inhibition of Na+ conductance, and depolarization of the basolateral membrane, due to stimulation of Cl- conductance, were observed. 8-(4-Chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, as a pure vascular AVP receptor 2 (V2) action, mimicked the actions of AVP. Addition of AVP (100 pM to 1 nM) in the lumen resulted in increases in lumen-negative VT and RT. Luminal AVP did not affect the electrical parameters in beta-intercalated cells. In principal cells, luminal AVP caused sustained increase in total membrane resistance (Ri), together with an initial depolarization of the luminal membrane followed by a late hyperpolarization of the basolateral membrane. Because the initial response was abolished in the presence of 2 mM Ba2+ in the lumen, an inhibition of luminal K+ conductance may be responsible for the initial phase of luminal AVP action. Late hyperpolarization of the basolateral membrane associated with an increase in membrane resistance was abolished in the absence of ambient Cl-. Under the condition where Cl- conductance of the basolateral membrane was stimulated by administration of cAMP in the bath, voltage deflections of the basolateral membrane on changing Cl- concentration in the bath from 120 to 12 mM decreased by 88% in the presence of luminal AVP. These observations are in accord with the view that the basolateral Cl- conductance was inhibited by luminal AVP in the later phase. These data indicate that AVP in the lumen inhibits basolateral Cl- conductance, which is stimulated by AVP in the bath.

Inhibition of amiloride-sensitive apical Na+ conductance by acetylcholine in rabbit cortical collecting duct perfused in vitro

We examined effects of acetylcholine (ACh) on the electrical parameters and intracellular Ca2+ concentration ([Ca2+]i) in the isolated rabbit cortical collecting duct (CCD) perfused in vitro using the conventional microelectrode technique and microscopic fluorescence spectrophotometry. ACh (10(-8) to 10(-5) M) in the bath caused a positive deflection of the transepithelial voltage (VT) and an increase in [Ca2+]i. Carbachol also showed similar but smaller effects. The effects of ACh were antagonized by muscarinic receptor antagonists. ACh at 10(-6) M hyperpolarized the apical membrane voltage and increased the fractional resistance of the apical membrane of the collecting duct cells accompanied by a positive deflection of VT and an increase in transepithelial resistance, whereas it did not affect these parameters in the beta-intercalated cells. In the presence of 10(-5) M amiloride in the lumen, the effects of ACh were almost completely abolished. The ACh-induced increase in [Ca2+]i is accounted for by the release of Ca2+ from intracellular store and Ca2+ entry from the bath. In the absence of Ca2+ in the bath, the ACh-induced changes in electrophysiological parameters were significantly smaller than those observed in the presence of Ca2+. Both phorbol-12-myristate-13-acetate (PMA) and phorbol-12,13-dibutylate (PDBu), activators of protein kinase C (PKC), also inhibited the apical Na+ conductance. In the presence of PMA or PDBu in the bath, ACh did not show further inhibitory effect. 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine, an inhibitor of PKC, partially attenuated the effect of ACh. These observations indicate that ACh inhibits the apical Na+ conductance partly by both increasing [Ca2+]i and activating PKC. Such an action of ACh may partially explain its natriuretic effect.

Pressure- and parathyroid-hormone-dependent Ca2+ transport in rabbit connecting tubule: role of the stretch-activated nonselective cation channel

To characterize the Ca2+ transport process across the apical membrane of the rabbit connecting tubule (CNT), we examined the effects of luminal pressure on parathyroid hormone (PTH)-dependent apical Ca2+ transport in this segment perfused in vitro. An increase of perfusion pressure (0.2 to 1.2 KPa) caused cytoplasmic free Ca2+ concentration ([Ca2+]i) to increase by 42 +/- 11 nM in Fura-2 loaded perfused CNT. The response was accentuated when 10 nM PTH was added to the bath (101 +/- 30 nM, n = 6). Addition of 0.1 mM chlorphenylthio-cAMP (CPT-cAMP) to the bath also augmented the [Ca2+]i response to pressure from 36 +/- 16 to 84 +/- 26 nM (n = 3). Under steady perfusion pressure at 1.2 KPa, PTH (10 nM) increased [Ca2+]i by 31 +/- 7 nM (n = 5), whereas it did only slightly by 6 +/- 2 nM (n = 12) at 0.2 KPa. The pressure-dependent increase of [Ca2+]i was abolished by removing luminal Ca2+ (n = 3), and was not affected by 0.1 and 10 microM nicardipine (n = 4) in the presence of 10 nM PTH. Cell-attached patch clamp studies on the apical membrane of everted CNT with pipettes filled with either 200 mM CaCl2 or 140 mM NaCl revealed channel activities with conductances of 42 +/- 2 pS (n = 4) or 173 +/- 7 pS (n = 5), respectively. An application of negative pressure (-4.9 KPa) to the patch pipette augmented its mean number of open channels (NPo) from 0.005 +/- 0.001 to 0.022 +/- 0.005 in the Ca(2+)-filled pipette, and was further accelerated to 0.085 +/- 0.014 (n = 3) by 0.1 mM CPT-cAMP. In the Na(+)-filled pipette, similar results were obtained (n = 3), and CPT-cAMP did not activate the stretch-activated channel in the absence of negative pressure (n = 3). These results suggest that a stretch-activated nonselective cation channel exists in the apical membrane of the CNT and that it is activated by PTH in the presence of hydrostatic pressure, allowing entry of Ca2+ transport from the apical membrane.

"Lipomatous" lesions of unknown cellular origin in the liver of B6C3F1 mice

The gross, microscopic, and ultrastructural features of lipomatous lesions in the liver of B6C3F1 mice are described. The cases were selected from a database of 45,406 male and 45,674 female mice used as treated, control, or vehicle-control animals in the National Cancer Institute's Bioassays or the National Toxicology Program's 2-year carcinogenicity studies. Thirteen hepatic lesions identified from cases within the database were re-evaluated microscopically and selected for further study. These lesions were present in ten males and three females that were between 85 and 113 weeks of age at the time of death. Grossly, the liver lesions were described as white to yellow or red to brown nodules/masses or foci that ranged from 2.0 to 25 mm in diameter. The lesions commonly involved the median and left lateral hepatic lobes. Microscopically, many of the lesions closely resembled lipomas described in the liver of human beings, and they consisted of nonencapsulated mature adipose-like tissue with irregular margins. The majority of the cells that comprised the lipomatous lesions were signet-ring shaped. These cells were positive for lipid as evidenced with oil red-O. The lipid droplets were also present within the hepatocytes that comprised the hepatic plates trapped within or surrounding many of the lipomatous lesions. At the margins of many of the lesions there were spindle-shaped cells that contained small intracytoplasmic lipid vacuoles. These cells were often within a stromal matrix that had focal areas of collagen and mucopolysaccharides, as evidenced by weak staining with Masson's trichrome and periodic acid-Schiff's stains, respectively. There was also disruption of the reticulum fibers in many of the lesions, as noted with a Gomori's reticulum stain. Ultrastructurally, cytoplasmic organelles, such as rough endoplasmic reticulum, free ribosomes and small lipid vacuoles, were present in the spindle-shaped cells, whereas signet-ring-shaped cells had few discernible organelles due to peripheral compression of the cytoplasm by single large vacuoles occupying the cytoplasmic space. The spindle-shaped cells were free of lysosomes. Thin collagen fibers were seen in contact with some of the spindle-shaped cells and were located between these cells and adjacent hepatocytes, or endothelial cells lining sinusoidal capillaries. A distinct basal lamina was not associated with spindle- or signet-ring-shaped cells. Similar lipomatous lesions were not found in other visceral organs. The exact cellular origin of the hepatic lesions described here is not known.

Cell Ca2+ response to luminal vasopressin in cortical collecting tubule principal cells

Although vasopressin V1 receptors have been shown to exist in both luminal and basolateral membranes of rabbit cortical collecting duct (CCD), exact cell types having V1 receptors remain unestablished. To identify the distribution of V1 receptor by cytoplasmic Ca2+ response, we utilized the confocal imaging system in the microperfused rabbit CCD. Basolateral application of arginine vasopressin (AVP) increased [Ca2+]i mainly in one group of cells which were not stained by fluorescein-isothiocyanate-conjugated peanut agglutinin. Luminal application of AVP increased [Ca2+]i in the same cells which responded to basolateral AVP. These findings provide evidence that V1 receptors, as defined by the [Ca2+]i response, exist in both luminal and basolateral membranes of the rabbit principal cell.

Isoproterenol stimulates Cl- current by a Gs protein-mediated process in beta-intercalated cells isolated from rabbit kidney

To examine the effect of isoproterenol on Cl- current and its signal transduction pathway in beta-intercalated cells (beta-IC cell), peanut agglutinin (PNA) positive cells in culture were studied by the whole-cell clamp technique. We identified these cells as beta-IC cells by PNA-binding, cell alkalinization induced by Cl- free in the superfusate, and an increase in intracellular cAMP concentration by isoproterenol, but not by vasopressin. Application of isoproterenol in the voltage-clamp mode induced an activation of Cl- current in a dose-dependent fashion and its threshold concentration was in the order of 0.01 microM and ED50 was about 0.1 microM. This effect of isoproterenol was inhibited by atenolol, a beta-adrenergic blocker. Either extracellular application of forskolin or intracellular application of cAMP mimicked the action of isoproterenol. In the presence of forskolin or cAMP, isoproterenol caused little further activation of Cl- current. A synthetic inhibitor of protein kinase A (5-24 amide) inhibited the Cl- -channel activation by isoproterenol. Isoproterenol failed to activate the current in the presence of intracellular GDP beta S. By contrast, intracellular application of GTP gamma S rendered irreversible the Cl- -channel activation by brief exposure to isoproterenol. The present studies provide direct evidence that in the PNA-binding cell, probably the beta-IC cell, the stimulation of beta-adrenoceptor activates Cl- current through the signal transduction system involving G-protein, adenylate cyclase, cAMP, and protein kinase A.

Regulation of Na(+)-3HCO3- cotransport in rabbit proximal convoluted tubule via adenosine A1 receptor

We investigated the role of adenosine A1-receptor in the regulation of basolateral Na(+)-3HCO3- cotransporter in the rabbit proximal convoluted tubule (PCT) microperfused in vitro by monitoring basolateral membrane potential and intracellular pH. FK-453, a highly specific A1 antagonist, inhibited basolateral HCO3- conductance in a concentration-dependent manner (10(-10)-10(-5) M). Other A1 antagonists, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) at 10(-5) M and theophylline at 10(-3) M, also had similar effects. N6-cyclohexyladenosine (CHA) at 10(-7) M attenuated the effect of low concentration (10(-8) M) of FK-453. Either enhancement of the degradation of adenosine by 0.1 U/ml adenosine deaminase (ADA) or inhibition of adenosine release from the cells by 10(-6) M S-(4-nitrobenzyl)-6-thioinosine (NBTI) mimicked the effects of A1 antagonists. These observations suggest that endogenous adenosine is released from PCT cells and stimulates Na(+)-3HCO3- cotransporter. Both 10(-4) M 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (CPT-cAMP) and 10(-6) M forskolin also inhibited basolateral HCO3- conductance. Both 10(-6) M FK-453 and 10(-4) M CPT-cAMP decreased the initial rate as well as the magnitude of intracellular acidification induced by reduction of peritubular HCO3- concentration from 25 to 0 mM. Neither 10(-6) M FK-453 nor 10(-7) M CHA changed intracellular Ca2+ concentration as measured by fura-2 fluorescence. These results indicate that adenosine might stimulate HCO3- exit across the basolateral membrane through Na(+)-3HCO3- cotransporter by decreasing intracellular cAMP via A1-receptor activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular heterogeneity of ammonium ion transport across the basolateral membrane of the hamster medullary thick ascending limb of Henle's loop

The epithelia of the medullary thick ascending limb (MAL) consists of two cell types, high (HBC) and low basolateral conductance (LBC) cell, depending on the K+ conductance of the basolateral membrane. The NH4+ conductance distinct from the K+ conductance has been suggested to exist in the proximal tubule, MAL cell, and Xenopus oocyte. The present study was designed to examine whether there is a conductive NH4+ transport system distinct from K+ conductance in two different cell types of the hamster MAL perfused in vitro. The basolateral membrane voltage (VB) was measured by impaling cells with conventional microelectrodes. Addition of NH4+ to the bath depolarized VB in a dose-dependent manner in both cell types. The response was maintained in the absence of HCO3-. When the VB deflection elicited upon 50 mM KCl or NH4Cl in the bath (delta VBK+ or delta VBNH4+) were compared, delta VBNH4+ was almost the same as delta VBK+ in the HBC cell, whereas the former was greater than the latter in the LBC. In the HBC cell, 10 mM Ba2+ in the bath equally suppressed both delta VBK+ and delta VBNH4+, whereas in the LBC cell it suppressed delta VBK+ with a small effect on delta VBNH4+, indicating that NH4+ is transported via a pathway distinct from Ba(2+)-sensitive K+ conductance. The VB deflection by NH4+ was unaffected by addition of 0.1 mM ouabain or 10 microM 5-nitro-2-(3-phenylpropylamino)-benzoate (a Cl- channel blocker) to the bath, excluding the contribution of the Na+, K+ pump or Cl- channel. An abrupt reduction of Na+ in the bath from 200 to 20 mM did not cause any changes in VB, suggesting that a nonselective cation channel may not account for the NH4+ transport. Amiloride at 10 microM inhibited delta VBNH4+ with a higher efficacy in the LBC cell. We conclude that a rheogenic NH4+ transport system independent from the K+ conductance exists in the basolateral membrane of the LBC cell of the hamster MAL, and may play some roles in the regulation of NH4+ transport.

Effects of amiloride and a novel diuretic, 7-chloro-2,3-dihydro-1-(2-methylbenzoyl)-4(1H)-quinolinone-4-oxime-o-su lfonic acid, potassium salt (M17055), on calcium transport in the rabbit connecting tubule

To elucidate the mechanisms of relative anticalciuric effect of a diuretic, 7-chloro-2,3-dihydro-1-(2-methylbenzoyl)-4(1H)-quinolinone-4-oxime-o-sul fonic acid, potassium salt (M17055), having sites of action on the Henle's loop plus the distal nephron segments, we measured intracellular calcium concentration ([Ca++]i) of the rabbit connecting tubule perfused in vitro by using the microscopic fluorometry with fura 2. First, we confirmed that parathyroid hormone increases [Ca++]i by a mechanism mediated by cyclic AMP. We also confirmed that the Na+/Ca++ exchanger in the basolateral membrane is essential for the extrusion of Ca++ across this membrane. In the presence of 10 nM parathyroid hormone in the bath, the elimination of Na+ from the lumen decreased [Ca++]i, supporting the view that a decrease in Na+ supply from the apical membrane enhances the Na+/Ca++ exchanger in the basolateral membrane. Under a similar condition, the addition of 10 microM amiloride in the lumen also decreased [Ca++]i, further supporting the view that the inhibition of Na+ entry across the apical membrane causes similar effect as does Na+ elimination. Under a similar condition, the addition of 1 mM M17055 in the lumen exerted a similar effect on [Ca++]i as did amiloride. Because M17055 did not further decrease [Ca++]i when Na+ was eliminated from the lumen, the effect of M17055 is mediated by an inhibition of Na+ entry across the apical membrane. From these observations we conclude that either inhibition or diminution of Na+ entry across the apical membrane of the connecting tubule increases the Ca++ extrusion across the basolateral membrane via the Na+/Ca++ exchanger.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a novel diuretic, 7-chloro-2,3-dihydro-1-(2-methylbenzoyl)-4(IH)-quinolinone-4-oxime-o- sulfonic acid, potassium salt (M17055) on Na+ and K+ transport in the distal nephron segments

By using an in vitro microperfusion technique, we examined whether a novel loop diuretic, 7-Chloro-2,3-dihydro-1-(2-methylbenzoyl)-4(IH)-quinolinone-4-oxime-o-sul fonic acid, potassium salt (M17055), a derivative of quinolinone oxime sulfonic acids, affects Na+ and K+ transport in the distal nephron segments, including the cortical collecting duct and connecting tubule (CNT) isolated from rabbit kidneys. M17055 added to the lumen at 1 mM caused a positive deflection of transepithelial voltage (VT) by 2.2 +/- 0.4 mV. The response was less than that evoked by 10 microM amiloride (8.9 +/- 0.1 mV). In the collecting duct cell of the cortical collecting duct from normal rabbits, M17055 depolarized the basolateral membrane by 9.2 +/- 1.3 mV, whereas amiloride hyperpolarized it by 7.6 +/- 2.4 mV. In the cortical collecting duct from deoxycorticosterone acetate-treated rabbits, despite the fact that both agents depolarized the basolateral membrane of the collecting duct cell, amiloride consistently hyperpolarized the apical membrane, whereas M17055 did not cause any significant changes in apical membrane voltage. In the presence of 2mM Ba++ in the lumen, the apical membrane voltage deflection by M17055 was abolished. In addition, the magnitude of the apical membrane voltage deflection caused by an abrupt increase in luminal K+ concentration from 5 to 50 mM was significantly reduced. In the CNT, both amiloride and M17055 caused a positive deflection of VT. However, M17055 depolarized the basolateral membrane by 6.6 +/- 1.6 mV, whereas amiloride hyperpolarized it by 4.4 +/- 1.1 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

Loop and distal actions of a novel diuretic, M17055

We investigated the mechanism of action of a novel 'high ceiling' diuretic, M17055, in in vivo clearance studies with anesthetized dogs during water diuresis and in vitro microperfusion studies of isolated rabbit renal tubules. In the clearance study, intravenous infusion of M17055 (1 mg/kg per h) decreased free water clearance and increased urinary excretion of Na+ and Cl- to a greater extent than did a maximum dose of furosemide (30 mg/kg per h). With the maximum dose of furosemide, an additional dose of M17055 or hydrochlorothiazide resulted in additional suppression of free water clearance. These results indicate that M17055 has some additional mechanisms of action in the distal nephron. In isolated rabbit cortical thick ascending limb of Henle's loop, M17055 applied to the lumen decreased the lumen positive transepithelial voltage at concentrations over 10(-6) M and suppressed the lumen-to-bath 36Cl- flux at 10(-5) M. In the connecting tubule, M17055 added to the lumen suppressed lumen negative transepithelial voltage in a concentration-dependent manner in a range from 10(-4) to 10(-3) M. The effect of M17055 on transepithelial voltage was also observed in the distal convoluted tubule and cortical collecting duct. Moreover, 10(-3) M of M17055 in the lumen significantly decreased the lumen-to-bath 22Na+ flux in the cortical collecting duct. From these observations, it appears that M17055 acts not only on the thick ascending limb of Henle's loop but also on the distal segments via inhibition of electrogenic Na+ transport.

Palpebral amelanotic melanomas in F344 rats

Spontaneous amelanotic melanomas in the eyelids of F344 rats were found in one of 1/926 (0.11%) male and 5/925 (0.54%) female F344 rats that were used as control and treated animals in five different carcinogenicity studies conducted by the National Toxicology Program (Research Triangle Park, NC). These melanomas were grossly recognized as single, tan or white, well-circumscribed masses of the right or left eyelid. These melanomas primarily occurred in the dermis of the skin of the eyelids and consisted of poorly differentiated spindle cells characteristically arranged in interlacing fascicles. Rarely, epithelioid tumor cells were also observed, and these tumor cells showed a negative histochemical reaction for melanin. The epidermis and dermal-epidermal junction were usually uninvolved. The diagnosis of amelanotic melanoma could only be established by electron microscopic examination. The most striking ultrastructural feature of the tumor cells was a large number of intracytoplasmic premelanosomes (stage II melanosomes without melanin), which nearly filled the cytoplasm of most tumor cells. Giant premelanosomes and melanophagosomes were also seen. The tumor cells did not possess the ultrastructural features characteristics of Schwann cells (thin, long cell processes and pericytoplasmic basal laminae). The histologic and ultrastructural features of these palpebral tumors were similar to those of cutaneous amelanotic melanomas of the pinna in F344 rats.

Effects of prostaglandin E2 on membrane voltage of the connecting tubule and cortical collecting duct from rabbits

1. Effects of prostaglandin E2 (PGE2) on ion transport were examined by observing the transmural (VT) and basolateral membrane voltage (VB) in the in vitro perfused rabbit connecting tubule (CNT) and the cortical collecting duct (CCD). 2. Addition of 1 microM PGE2 to the bath induced a biphasic response of transmural voltage (VT), with initial negative VT deflection followed by positive deflection in the CNT, but monophasic negative deflection in the CCD. Because PGE2 had no affect on the basolateral membrane voltage (VB), PGE2 mainly causes changes in the apical membrane voltage. 3. Elimination of Na+ from the lumen abolished the PGE2-induced VT response in the CNT. In the presence of 10 microM luminal amiloride, PGE2 caused only an initial negative deflection without causing later positive deflection. The positive VT deflection induced by PGE2 in the CCD was also blocked by luminal amiloride. 4. Addition of ouabain (0.1 mM) to the bath completely abolished the PGE2-induced VT changes in the CNT, indicating that an intact Na(+)-K+ pump is a prerequisite for the VT response to PGE2. 5. Addition of 2 mM Ba2+ to the lumen did not affect biphasic VT response to PGE2, indicating that Ba(2+)-sensitive K+ conductance is not involved. 6. Basolateral addition of 0.1 mM 8-(4-chlorophenylthio)-cAMP inhibited only the negative VT deflection induced by PGE2. 7. The positive VT deflection was blocked by basolateral addition of 50 microM 8-(N,N-diethylamino)octyl 3,4,5-trimethoxy benzoate hydrochloride (TMB-8), an inhibitor of intracellular Ca2+ release. But elimination of luminal Ca2+ did not affect the biphasic response to PGE2. 8. These findings suggest that the initial negative VT deflection is caused by an increase in Na+ influx across the luminal membrane through an amiloride-insensitive Na+ conductive pathway, whereas the later positive deflection is caused by the inhibition of Na+ influx through the amiloride-sensitive Na+ conductive pathway. The cAMP messenger system may be responsible for the initial negative deflection, whereas an increased intercellular Ca2+ release from the store is necessary for the later positive deflection caused by PGE2. The response in the CCD is comparable to the later response in the CNT.

Regulation of cortical collecting duct function: effect of endothelin

We recently showed that endothelin-1 (ET-1) increases cell Ca2+ in the mouse cortical collecting duct. To clarify the cellular action and target cell of ET-1, electrophysiologic techniques and cell Ca2+ measurement were applied to rabbit cortical collecting ducts perfused in vitro. When 10(-8) mol/L ET-1 was added to the bath, a transient increase followed by a sustained increase in cell Ca2+ was observed. A sustained increase in cell Ca2+ lasted 10 to 20 minutes and was associated with a decrease in lumen-negative transepithelial voltage. To confirm the target cell type of ET-1, confocal laser microscopy was used. An increase in cell Ca2+ was observed in the same cell, which also showed an increase in cell Ca2+ in response to arginine vasopressin (AVP), which indicated that the principal cell has ET-1 receptors in the basolateral membrane. When ET-1 was applied to the bath, total cellular membrane resistance (Ri) decreased initially and then gradually increased because of inhibition of the luminal Na+ channel. An initial decrease in Ri was considered an influx of Ca2+ from the basolateral membrane. To further determine the source of an increase in cell Ca2+, the effect of ET-1 was tested in the absence of external Ca2+ and in the presence of a Ca2+ channel blocker in the bath. Cell Ca2+ did not respond to ET-1 in the absence of external Ca2+, a condition in which an AVP-stimulated increase in cell Ca2+ was preserved.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of calcium transport across the basolateral membrane of the rabbit cortical thick ascending limb of Henle's loop

Although net Ca2+ absorption takes place in the thick ascending limb of Henle's loop, detailed mechanisms are unknown. Because it has been reported that the Ca2+ entry step across the luminal membrane is mediated by Ca2+ channels inserted by stimulation with parathyroid hormone, we studied the mechanism of Ca2+ transport across the basolateral membrane of rabbit cortical thick ascending limb (CTAL) perfused in vitro by using microscopic fluorometry of cytosolic Ca2+ ([Ca2+]i) with fura-2. The resting [Ca2+]i in this segment was 49.8 +/- 4.5 nmol/l. Neither Na+ removal from the bathing solution nor addition of ouabain (0.1 mmol/l) to the bath increased [Ca2+]i, indicating that a Na+/Ca2+ exchanger in the basolateral membrane may not contribute in any major way to [Ca2+]i of CTAL. To confirm our technical accuracy, similar protocols were conducted in the connecting tubule, where the existence of a Na+/Ca2+ exchanger has been reported. In this segment, Na+ removal from the bath increased cell Ca2+ from 148.6 +/- 6.4 nmol/l to 647.6 +/- 132.0 nmol/l, confirming the documented fact. [Ca2+]i in the CTAL was markedly increased when 1 mmol/l NaCN was added to the bath in the absence of glucose. Calmodulin inhibitors (trifluoperazine or W-7) increased [Ca2+]i. When the bath pH was made alkaline, [Ca2+]i was also increased. This response was abolished when Ca2+ was eliminated from the bath, indicating that the Ca2+ entry across the basolateral membrane is dependent on bath pH. Increase in [Ca2+]i induced by an alkaline bath was inhibited by increased the bath K+ from 5 nmol/l to 50 mmol/l, suggesting that the Ca2+ entry system is voltage-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of PGE2-induced cell swelling in distal nephron segments

The effects of prostaglandin (PG) E2 on cell swelling were studied in isolated perfused tubules of rabbit kidney. PGE2 (1 microM) added to the bath induced cell swelling by 13.4, 7.2, and 9.6% in the connecting tubule, distal convoluted tubule, and cortical collecting duct, respectively, but it had no effect on the proximal convoluted tubule and cortical thick ascending limb. The response was dose dependent in the range of 1 nM to 1 microM. PGI2 exerted a similar effect, but PGF2 alpha had no effect. The swelling was completely blocked by basolateral Na+ removal and was attenuated by bilateral Cl- removal, suggesting that the swelling was mediated by basolateral Na+ entry in association with Cl- entry. In all segments except proximal tubule, PGE2 caused an initial transient peak followed by a sustained increase in intracellular Ca2+. Intracellular Ca2+ chelation or inhibition of Ca2+ release from intracellular stores abolished the PGE2-induced cell swelling, but extracellular Ca2+ removal did not. An inhibitor of the Na(+)-Ca2+ exchanger (3',4'-dichlorobenzamil, 100 microM) in the bath completely inhibited PGE2-induced cell swelling. Neither furosemide (1 mM) nor amiloride (1 mM) added to bath abolished the response, indicating that neither Na(+)-K(+)-2Cl- cotransport nor Na(+)-H+ exchange is involved in the action of PGE2. The swelling response to PGE2 was observed even in the presence of ouabain, indicating that the effect of PGE2 is independent of Na(+)-K(+)-adenosinetriphosphatase inhibition. Nicardipine added to bath partially inhibited the swelling response.(ABSTRACT TRUNCATED AT 250 WORDS)

[Measurement of intracellular pH]

Since various cellular processes depend on changes in pH, the regulation of intracellular pH (pHi) is important both for the individual cell and for the organism. The mechanisms of the regulation of pHi can be investigated by monitoring pHi. In this report, we discuss the four major techniques available for measuring pHi, which are 1) Distribution of weak acids and bases, 2) pH-sensitive microelectrodes, 3) pH-sensitive dyes, and 4) Nuclear magnetic resonance. Among four techniques, the advantage of the microelectrode approach is that it can monitor membrane potential at the same time and be applied to a single cell. The dye technique is a relative new developing technique, which has lots of advantages. It is easy to use, and is capable of monitoring rapid pHi changes, and being applied to a smaller cell, or a single cell.

Intraocular and orbital malignant schwannomas in F344 rats

Intraocular and orbital malignant Schwannomas in two F344 rats are presented. The two Schwannomas were identified among approximately 60,000 male and 60,000 female F344 rats. The intraocular malignant Schwannoma occurred in the iris, invading the corneal stroma through the destroyed Descemet membrane. The malignant orbital Schwannoma occurred in the left orbit, invading the contralateral orbit along the optic nerve. Histologically, the intraocular Schwannoma consisted predominantly of a perivascular fascicular pattern of plump spindle cells associated with marked cytoplasmic vacuolization. The orbital Schwannoma consisted of Antoni type A and B pattern, but Antoni B tissues predominated. Antoni A tissues consisted of closely packed, elongated spindle cells arranged in interlacing fascicles, while Antoni B tissues were highly cellular and consisted of anaplastic, small cells associated with marked cyst formation. Immunohistochemically, the intraocular Schwannoma had a positive immunoreactivity for S-100 protein, while the orbital Schwannoma had a negative immunoreactivity. Ultrastructurally, the cells of both intraocular and orbital Schwannomas had long, thin cell processes and pericytoplasmic basal laminae. Particularly, the plump spindle cells of the intraocular Schwannoma were most strikingly characterized by the well developed, extremely attenuated cell processes arranged in a lamellar or spiral pattern. These cell processes and cell bodies were associated with numerous desmosomes. Intracytoplasmic filamentous granules and bodies, consisting of intermediate filaments approximately 7 nm in width, were additional characteristics of the plump spindle cells.

Effect of protamine on ion conductance of ascending thin limb of Henle's loop from hamsters

To evaluate the contribution of paracellular shunt pathway in ascending thin limb (ATL) of hamsters, we examined the effect of protamine, a selective blocker of paracellular conductance, on salt-diffusion voltage (dVT) and transmural resistance (RT) during in vitro microperfusion. Lumen-negative dVT generated on reduction of lumen NaCl concentration was increased further from -7.3 +/- 0.5 to -10.3 +/- 0.7 mV when 300 micrograms/ml protamine was added to the lumen, and calculated Na+/Cl- permeability ratio was decreased from 0.46 +/- 0.03 to 0.31 +/- 0.03. Although the effect of protamine persisted after removal of the agent from the lumen, addition of 30 U/ml heparin returned the dVT toward the control level. The effect of protamine was dose dependent from 30 to 300 micrograms/ml. Protamine also exerted its effect from the bath, and the effect was inhibited by heparin either from the lumen or from the bath. The inhibitory effect was almost the same when the orientation of imposed NaCl gradient was reversed. Inhibition of transcellular Cl- transport with 0.1 mM 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) in the bath caused lumen-positive dVT. This voltage was decreased significantly by protamine. Protamine markedly decreased the apparent transference number for Na+ but slightly increased the value for Cl-. Transmural cable analysis showed that 300 micrograms/ml protamine added to the lumen increased RT from 0.59 +/- 0.10 to 1.20 +/- 0.20 omega.cm2, with the effect being reversed by 30 U/ml heparin.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous amelanotic melanomas of the uveal tract in F344 rats

Five intraocular amelanotic melanomas were identified in the National Toxicology Program's database consisting of records from more than 60,000 female and 60,000 male F344 rats, which were used as control and treated animals in 2-year carcinogenicity studies. The five spontaneous melanomas were grossly observed as white or yellow, unilateral nodules, which originated in the region of the iris and ciliary body, often also involving the choroid. These amelanotic melanomas were composed predominantly of spindle cells arranged in a whorled pattern often with perivascular orientation. Mitotic figures were common in five tumors. The spindle cells had a positive immunoreactivity for S-100 protein but were negative for desmin. Electron microscopic studies provided clear evidence that these tumors originated from the uveal melanocytes. Ultrastructurally, the spindle cells contained numerous cytoplasmic premelanosomes (stage II melanosomes) that were not associated with melanin. Special histochemical studies showed that the spindle cells had a negative reaction for melanin. Although electron microscopic features are critical in the diagnosis of amelanotic melanomas of the uveal tract, the whorled pattern of spindle cells is a useful histologic criterion in differential diagnosis of this tumor in F344 rats.

Interaction of trichlormethiazide or amiloride with PTH in stimulating Ca2+ absorption in rabbit CNT

To determine the renal tubular site and mechanism of the anticalciuric effects of trichloromethiazide (TCM) and amiloride, we studied the effects of these diuretics on net Ca2+ absorption (JCa) in isolated rabbit connecting tubules (CNT) and cortical collecting ducts (CCD). TCM (100 microM) in the lumen increased JCa in the CNT without affecting lumen-negative transepithelial voltage (VT). This effect was dependent on the amount of parathyroid hormone (PTH, 0.1 or 1 nM) in the bath. TCM had no detectable effect on JCa in the absence of PTH. Addition of 100 microM ouabain to the bath decreased PTH-stimulated JCa and abolished the TCM-stimulated JCa. Elimination of Na+ from the lumen increased PTH-stimulated JCa. Under this condition the ability of TCM to increase JCa was abolished, suggesting that the inhibition of Na+ entry from the lumen with TCM may account for the increase in PTH-stimulated JCa. Elimination of Na+ from the bath in the presence of PTH decreased JCa and abolished the stimulatory effect of TCM on JCa in the presence of PTH. Changes in VT caused by amiloride may not account for the increase in JCa, because JCa was not changed when VT was deflected to more positive direction by increasing bath K+ from 5 to 15 mM. Neither TCM nor amiloride affected JCa in the CCD. From these observations, we speculate that the inhibition of Na+ entry across the apical cell membrane by either thiazides or amiloride may stimulate PTH-induced JCa. The intact Na(+)-Ca2+ antiporter in the basolateral cell membrane is essential for the anticalciuric effect of thiazides and amiloride.

Selectivity of ion permeability across ascending thin limb of Henle's loop: interaction of Cl- and other halogens with anion transport system

In hamster ascending thin limb of Henle's loop (ATL) perfused in vitro, we examined halogen selective permeability and effects on Cl- transport. Relative permeabilities for halogens to sodium (PX/PNa) were determined by single salt dilution voltage. (PF/PNA, PCl/PNa, PBr/PNa and PI/PNa were 0.47 +/- 0.09, 3.23 +/- 0.22, 3.23 +/- 0.26, and 0.47 +/- 0.09, respectively. Simultaneous determination of 36Cl and 125I fluxes confirmed that addition of 10(-4) M 5-nitro-2-(3-phenyl-propylamino)-benzoate (NPPB), a Cl- channel blocker, to the bath decreased the flux coefficient for 36Cl (10(-7) cm2/s) from 67.0 +/- 11.7 to 29.5 +/- 7.9 without affecting that for 125I. NPPB also reduced both PCl/PNa and PBr/PNa from 2.67 +/- 0.20 to 0.95 +/- 0.12 and from 2.33 +/- 0.24 to 1.32 +/- 0.12, respectively. Addition of 100 mM Cl- or I- decreased 36Cl flux coefficient from 124.8 +/- 14.3 to 87.7 +/- 13.0 or to 41.0 +/- 11.6 without affecting that for 125I. All other halogens and SCN- also exhibited inhibitory effects on 36Cl flux. These findings support the hypothesis that the putative Cl- channel in the ATL is highly permeable to both Cl- and Br- but less permeable to I-, F-, and SCN-. They suggest that there are at least two functionally distinct components in the process of Cl- transport across the ATL, the binding site and the selective barrier. All halogens may compete against Cl- at the binding site.

Effect of protamine on ion conductance of upper portion of descending limb of long-looped nephron from hamsters

To estimate the contribution of paracellular shunt pathway to the cation-selective permeability in the upper portion of the descending limb of long-looped nephron (LDLu) of hamsters, we observed the effect of protamine on salt-diffusion voltage (delta VT) and transmural resistance (RT). delta VT generated on reduction of lumen NaCl concentration was decreased from 12.0 +/- 1.4 to 7.3 +/- 1.2 mV when 100 micrograms/ml protamine were added to the lumen. Although the effect of protamine persisted after removal of the agent from the lumen, addition of 30 U/ml heparin reversed the delta VT toward the control level. The effect of protamine was dose dependent in the range from 3 to 1,000 micrograms/ml. Protamine was without effect from the bath. Studies on single salt dilution voltage revealed that 100 and 300 micrograms/ml protamine inhibited relative Na+ to Cl- permeability from 4.03 +/- 0.38 to 2.14 +/- 0.21 and from 3.75 +/- 0.37 to 1.36 +/- 0.09, respectively. Protamine markedly decreased the apparent transference number for Na+ but slightly increased the value for Cl-. Protamine also inhibited permeabilities for K+, Rb+, and Li+ relative to Cl-, indicating that the inhibitory effect of protamine was not confined to Na+ but was generalized to cations. Transmural cable analysis showed that 100 micrograms/ml protamine increased RT from 14.0 +/- 1.1 to 19.3 +/- 1.2 omega.cm2, with the effect being reversed by 30 U/ml heparin. Because the effect of protamine on RT was unaffected by ouabain in the bath, changes in RT may mainly represent those of the paracellular shunt resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological characterization of upper portion of descending limb of long-looped nephron

The upper portion of the descending limb of long-looped nephron (LDLu) of the hamster is characterized by high water and ion permeabilities. Although the paracellular route is considered to be the major pathway representing cation permselectivity of this segment, ion transport mechanisms through the transcellular pathway are unknown. To study this issue; we applied cable analysis and conventional microelectrode technique to the hamster LDLu perfused in vitro. The transmural voltage (VT) was not different from zero, and transmural resistance (RT) was very low, 18.3 +/- 2.0 omega.cm2 (n = 12). The basolateral membrane voltage was -80 +/- 2 mV (n = 55), and fractional apical membrane resistance was 0.92 +/- 0.23 (n = 5). Ouabain (0.1 mM) in the bath decreased basolateral membrane voltage (VB) by 23 +/- 3 mV (n = 6, P less than 0.001). Increase in K+ concentration in bath and in lumen from 5 to 50 mM decreased VB by 39 +/- 2 (n = 7, P less than 0.01) and apical membrane voltage (VA) by 10 +/- 1 mV (n = 7, P less than 0.001), respectively. Addition of 2 mM Ba2+ to bath and to lumen decreased VB by -47 +/- 2 (n = 11, P less than 0.001) and decreased VA by 8 +/- 1 mV, respectively. Reduction of HCO3- in bath from 25 to 2.5 mM decreased VB by 4 +/- 1 mV (n = 7, P less than 0.005). Reduction of bath Cl- did not cause any rapid deflection of VB. No appreciable Na+ conductance was detected in the apical membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological identification of alpha- and beta-intercalated cells and their distribution along the rabbit distal nephron segments

By cable analysis and intracellular microelectrode impalement in the in vitro perfused renal tubule, we identified alpha- and beta-intercalated (IC) cells along the rabbit distal nephron segments, including the connecting tubule (CNT), the cortical collecting duct (CCD), and the outer medullary collecting duct in the inner stripe (OMCDi). IC cells were distinguished from collecting duct (CD) cells by a relatively low basolateral membrane potential (VB), a higher fractional apical membrane resistance, and apparent high Cl- conductances of the basolateral membrane. Two functionally different subtypes of IC cells in the CCD were identified based on different responses of VB upon reduction of the perfusate Cl- from 120 to 12 mM: the basolateral membrane of beta-IC cells was hyperpolarized, whereas that of alpha-IC cells was unchanged. This is in accord with the hypothesis that the apical membrane of beta-IC cells contains some Cl(-)-dependent entry processes, possibly a Cl-/HCO3- exchanger. Further characterization of electrical properties of both subtypes of IC cells were performed upon lowering bath or perfusate Cl- from 120 to 12 mM, and raising bath or perfusate K+ from 5 to 50 mM. A 10-fold increase in the perfusate K+ had no effect on VB in both subtypes of IC cells. Upon abrupt changes in Cl- or K+ concentration in the bath, a large or a small depolarization of the basolateral membrane, respectively, was observed in both subtypes of IC cells. The electrical properties of alpha- and beta-IC cells were similar among the distal nephron segments, but their distribution was different: in the CNT, which consists of IC cells and CNT cells, 97.3% (36/37) of IC cells were of the beta type. In the CCD, which consists of IC cells and CD cells, 79.8% (79/99) of IC cells were of the beta-type, whereas in the OMCDi 100% (19/19) were of the alpha type, suggesting that the beta type predominates in the earlier and the alpha type in the later segment.

Fordyce's granules of the incisor and molar gingiva in F344 rats

Fordyce's granules were observed in the gingiva of the upper incisor and molar teeth in F344 rats. The data were based on 734 males and 722 females that were used as control and treated animals in 26-week, 65-week, and 2-year studies by the National Toxicology Program. The incidence of Fordyce's granules was markedly different when comparing sex, age, and site of the lesion. Fordyce's granules were very common in the midsagittal gingiva of the upper incisor in males and increased in incidence with age (34.2, 50, and 56.3% in 26-week, 65-week, and 2-year studies, respectively). The granules of the incisor gingiva were rare in females (0,0, and 2.8% in 26-week, 65-week, and 2-year studies, respectively). Fordyce's granules of the molar gingiva were very rare in both sexes and were found only in 9/734 (1.2%) males and in 3/722 (0.4%) females. Only three unilateral granules of the molar were grossly recognized as focal swelling of the gingiva or a white nodule with a huge cyst in the third upper molar. Histologically, Fordyce's granules were arranged as a collection of sebaceous glands unassociated with hair follicles. In addition, the granules of the molar gingiva were associated with cystically dilated ducts filled with sebum. Ultrastructurally, the sebaceous cells were characterized by varying numbers of cytoplasmic lipid droplets and occasional desmosome and hemidesmosome formation. Fordyce's granules previously reported in rats of other strains were also reviewed and compared with those in F344 rats in regard to incidence, location, and age.

Effects of PTH, calcitonin, and cAMP on calcium transport in rabbit distal nephron segments

Distal nephron segments are heterogenous with respect to adenylate cyclase responses to stimulation with parathyroid hormone (PTH) or calcitonin (CT). We examined effects of these hormones and of 8-(p-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (CPTcAMP) on net Ca absorption (Jnet Ca2+, pmol.min-1.mm-1) in rabbit distal nephron segments by in vitro microperfusion technique. We studied three segments, including distal convoluted tubule (DCT), connecting tubule (CNT), and cortical collecting duct (CCD). PTH (1 nM) in bath significantly increased Jnet Ca2+ from 2.28 +/- 0.35 to 9.44 +/- 1.13 in CNT, but did not affect Jnet Ca2+ in DCT or CCD. CT (1 nM) in bath significantly increased Jnet Ca2+ from 1.58 +/- 0.29 to 4.45 +/- 1.01 in DCT, whereas it did not affect Jnet Ca2+ either in CNT or in CCD. CPTcAMP (30 microM) in bath significantly increased Jnet Ca2+ from 2.29 +/- 0.42 to 3.97 +/- 0.43 in DCT and from 2.43 +/- 0.18 to 5.83 +/- 0.37 in CNT, but it did not affect Jnet Ca2+ in CCD. When Na+ was removed from bathing fluid or when 0.1 mM ouabain was added to bath, Jnet Ca2+ in both DCT and CNT significantly decreased. Furthermore, stimulatory effects of PTH and CT on Ca2+ absorption in the respective segments were abolished under these conditions. These results suggest that PTH and CT increase Ca2+ absorption in CNT and DCT, respectively, through cAMP-mediated mechanisms. Presence of a basolateral Na(+)-Ca2+ exchange process seems to be a prerequisite for effects of these hormones. However, exact intracellular mechanisms remain uncertain.

Mechanisms of intracellular pH regulation in the hamster inner medullary collecting duct perfused in vitro

To examine the mechanisms of H+ transport in the mid-inner medullary collecting duct of hamsters, we measured the intracellular pH (pHi) in the in vitro perfused tubules by microscopic fluorometry using 2',7'-bis(carboxyethyl)-carboxyfluorescein (BCECF) as a fluorescent probe. In the basal condition, pHi was 6.74 +/- 0.04 (n = 45) in HCO3(-)-free modified Ringer solution. Either elimination of Na+ from the bath or addition of amiloride (1 mM) to the bath produced a reversible fall in pHi. After acid loading with 25 mM NH4Cl, pHi spontaneously recovered with an initial recovery rate of 0.096 +/- 0.012 (n = 23) pH unit/min. In the absence of ambient Na+, after removal of NH+4, the pHi remained low (5.95 +/- 0.10, n = 8) and showed no signs of recovery. Subsequent restoration of Na+ only in the lumen had no effect on pHi. However, when Na+ in the bath was returned to the control level, pHi recovered completely Amiloride (1 mM) in the bath completely inhibited the Na(-)-dependent pHi recovery. Furthermore, elimination of Na+ from the bath, but not from the lumen, decreased pHi from 6.97 +/- 0.07 to 6.44 +/- 0.05 (n = 12) in the HCO3-/Ringer solution or 6.70 +/- 0.03 to 6.02 +/- 0.5 pH unit/min in the presence of CO2/HCO3-, whereas it did not recover in the absence of CO2/HCO3-.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of parathyroid hormone on the connecting tubule from the rabbit kidney: biphasic response of transmural voltage

The effect of parathyroid hormone (PTH) on ion transport was examined by observing transmural (VT) and basolateral membrane voltage (VB) in the in vitro perfused rabbit connecting tubule. Addition of 10 nmol/l PTH to the bath induced a biphasic response of VT, with hyperpolarization followed by depolarization. Chlorophenylthioadenosine cyclic 3',5'-monophosphate mimicked the effect of PTH, which did not change the VB in the connecting tubule cell, but mainly caused changes in the apical membrane voltage. The VT of distal convoluted tubule and the cortical collecting duct were not affected by PTH. Elimination of Na+ from the lumen abolished the PTH-induced VT responses in the connecting tubule. In the presence of 10 mumol/l amiloride, PTH caused an initial hyperpolarization but did not induce the late depolarization. The same was seen in the absence of luminal Ca2+. Either addition of 0.1 mmol/l ouabain to the bath or elimination of bath Na+ completely abolished the PTH-induced VT changes. The presence of 5 mmol/l Ba2+ in the lumen did not affect the response to PTH. These findings indicate that the initial hyperpolarization may be caused by an increase in Na+ influx across the luminal membrane through an amiloride-insensitive Na+ conductive pathway and that the late depolarization may be caused by the decrease in Na+ influx through the amiloride-sensitive Na+ conductive pathway. Luminal Ca2+ is necessary for the late depolarization caused by PTH.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological study of inner medullary collecting duct of hamsters

The electrophysiological properties of the hamster mid-inner medullary collecting duct (IMCD2) cells were examined in isolated and perfused preparations by intracellular impalement with conventional 1 mol/l KCl microelectrodes and cable analysis. The transmural voltage (VT) was not different from 0 mV, while the basolateral transmembrane voltage (VB) was -81.7 +/- 0.91 mV (n = 221). The transmural resistance (RT) was 109 omega cm2, indicating that the IMCD2 is composed of tight epithelia. The fractional apical membrane resistance (fRA) was 0.98 +/- 0.003 (n = 10). Abrupt changes in the luminal concentration of Na+, K+ or Cl- did not alter the apical membrane voltage (VA) or VT, and neither 2 mmol/l Ba2+ nor 10 mumol/l amiloride in the lumen affected VA and VT. Moreover, pretreatment of hamsters with deoxycorticosterone acetate (5 mg/kg, s.c.) for 10-14 days caused only a very small change in VT in the negative direction. Amiloride in the lumen increased RT and increased the voltage divider ratio very slightly. However, an abrupt increase in K+ concentration in the bath from 5 mmol/l to 50 mmol/l or addition of 2 mmol/l Ba2+ to the bath depolarized the basolateral membrane by 39 mV and 29 mV, respectively. In the presence of 2 mmol/l Ba2+ in the bath, a reduction of HCO3- concentration from 25 mmol/l to 2.5 mmol/l depolarized VB by 20.4 mV. No Cl- conductance was demonstrated in the basolateral membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of water transport across the upper portion of the descending thin limb of long-looped nephron of hamsters

The mechanisms of water transport across the upper portion of the descending limb of long-looped nephron (LDLu) were examined by microperfusion of segments isolated from hamster kidneys. Because of cation permselectivity a streaming voltage was generated when a transmural osmotic gradient was imposed. When 100 mmol/l urea was added to the bath, the streaming voltage was -4.9 +/- 0.4 mV. Addition of 10(-4) mol/l parachloromercuribenzene sulfonate (PCMBS) decreased the voltage to -2.4 +/- 0.7 mV. This effect was associated with changes in osmotic water permeability (Pf, 10(-3) cm/s) from 243 +/- 42 to 47 +/- 15. PCMBS also decreased the transmural diffusional water permeability (Pdw, 10(-3) cm/s) from 9.4 +/- 0.6 to 7.2 +/- 0.6. The inhibitory effect of PCMBS was prevented by pretreatment with dithiothreitol. N-Butanol permeability was measured as an index of cellular resistance for diffusion. Large differences between Pf and Pdw can be explained both by cellular resistance to diffusion and by resistance through a water channel with a single file mechanism. The apparent activation energy for water transport, 13.3 x 10(3) joule/mol (3.16 kcal/mol), was low. These findings are compatible with the hypothesis that a water channel exists in this segment. PCMBS also inhibited the NaCl diffusion voltage, a parameter indicating cation permselectivity, in parallel with suppression of the streaming voltage, suggesting that the water channel is in part associated with cation permselectivity. The possibility that the PCMB-sensitive cation-permselective pathway exists in parallel cannot be ruled out.

Effect of high NaCl intake on Na+ and K+ transport in the rabbit distal convoluted tubule

Morphological studies have demonstrated that a chronic increase in distal Na+ delivery causes hypertrophy of the distal convoluted tubule (DCT). To examine whether high NaCl-intake also causes functional changes in the well defined DCT, we measured transmural voltage (VT), lumen-to-bath Na+ flux (JNa(LB], and net K+ secretion (JK(net] in DCTs obtained from control rabbits and those on high NaCl-intake diets. The lumen negative VT was significantly greater in the high NaCl group than in the control group. The net K+ secretion (pmol mm-1 min-1) was greater in the high NaCl-intake group (54.1 +/- 13.0 vs 14.7 +/- 5.6). The K+ permeabilities in both luminal and basolateral DCT membranes, as assessed by the K+-induced transepithelial voltage deflection inhibitable with Ba2+, were increased in the experimental group. The lumen-to-bath 22Na flux (pmol mm-1 min-1) was also greater in the experimental group (726 +/- 119 vs 396 +/- 65). The VT component inhibitable with amiloride was also elevated in the high NaCl-intake group. Furthermore, Na+-K+-ATPase activity of the DCT was higher in the experimental than in the control group. We conclude that high NaCl intake increases both Na+ reabsorption and K+ secretion by the DCT. This phenomenon is associated with an increased Na+-K+-ATPase activity along with increased Na+ and K+ permeabilities of the luminal membrane, and an increase in the K+ permeability of the basolateral membrane. Cellular mechanisms underlying these functional changes remain to be established.

Electrophysiological characterization of rabbit distal convoluted tubule cell

The distal convoluted tubule (DCT) from rabbit kidney were perfused in vitro to study the conductive properties of the cell membranes by using electrophysiological methods. When the lumen and the bath were perfused with a bicarbonate free solution buffered with HEPES, the transepithelial voltage (VT) averaged -2.8 +/- 0.6 mV (n = 20), lumen negative. The basolateral membrane voltage (VB) averaged -77.8 +/- 1.1 mV (n = 33) obtained by intracellular impalement of microelectrodes. Cable analysis performed by injecting a current from perfusion pipette revealed that the transepithelial resistance was 21.8 +/- 1.7 omega.cm2 and the fractional resistance of the luminal membrane was 0.78 +/- 0.03 (n = 8), indicating the existence of ionic conductances in the luminal membrane. Addition of amiloride (10(-5) mol/l) to the luminal perfusate or Na+ removal from the lumen abolished the lumen negative VT and hyperpolarized the apical membrane. An increase in luminal K+ concentration from 5 to 50 mmol/l reduced the apical membrane potential (VA) by 37.5 +/- 2.6 mV (n = 7), whereas a reduction of Cl- in the luminal perfusate did not change VA significantly (0.5 +/- 0.5 mV, n = 4). Addition of Ba2+ to the lumen reduced VA by 42.6 +/- 1.0 mV (n = 4). When the bathing fluid was perfused with 50 mmol/l K+ solution, the basolateral membrane voltage (VB) fell from -76.8 +/- 1.5 to -31.0 +/- 1.3 mV (n = 18), and addition of Ba2+ to the bath reduced VB by 18.3 +/- 4.8 mV (n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)