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Paszek AA, Wilkie PJ, Flickinger GH, Miller LM, Louis CF, Rohrer GA, Alexander LJ, Beattie CW, Schook LB. Interval mapping of carcass and meat quality traits in a divergent swine cross. Anim Biotechnol 2001; 12:155-65. [PMID: 11808631 DOI: 10.1081/abio-100108342] [Citation(s) in RCA: 35] [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: 11/03/2022]
Abstract
An autosomal scan of the swine genome with 119 polymorphic microsatellite (ms) markers and data from 116 F2 barrows of the University of Illinois Meishan x Yorkshire Swine Resource Families identified genomic regions with effects on variance in carcass composition and meat quality at nominal significance (p-value <0.05). Marker intervals on chromosomes 1, 6, 7, 8 and 12 (SSC1, SSC6, SSC7, SSC8, SSC12) with phenotypic effects on carcass length, 10th rib backfat thickness, average backfat thickness, leaf fat, loin eye area and intramuscular fat content confirm QTL effects identified previously based on genome wide significance (p-value <0.05). Several marker intervals included nominally significant (p-value <0.05) dominance effects on leaf fat, 10th rib backfat thickness, loin eye area, muscle pH and intramuscular fat content.
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Affiliation(s)
- A A Paszek
- Food Animal Biotechnology Center, Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108, USA
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Balog EM, Fruen BR, Shomer NH, Louis CF. Divergent effects of the malignant hyperthermia-susceptible Arg(615)-->Cys mutation on the Ca(2+) and Mg(2+) dependence of the RyR1. Biophys J 2001; 81:2050-8. [PMID: 11566777 PMCID: PMC1301678 DOI: 10.1016/s0006-3495(01)75854-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [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: 11/16/2022] Open
Abstract
The sarcoplasmic reticulum (SR) Ca(2+) release channel (RyR1) from malignant hyperthermia-susceptible (MHS) porcine skeletal muscle has a decreased sensitivity to inhibition by Mg(2+). This diminished Mg(2+) inhibition has been attributed to a lower Mg(2+) affinity of the inhibition (I) site. To determine whether alterations in the Ca(2+) and Mg(2+) affinity of the activation (A) site contribute to the altered Mg(2+) inhibition, we estimated the Ca(2+) and Mg(2+) affinities of the A- and I-sites of normal and MHS RyR1. Compared with normal SR, MHS SR required less Ca(2+) to half-maximally activate [(3)H]ryanodine binding (K(A,Ca): MHS = 0.17 +/- 0.01 microM; normal = 0.29 +/- 0.02 microM) and more Ca(2+) to half-maximally inhibit ryanodine binding (K(I,Ca): MHS = 519.3 +/- 48.7 microM; normal = 293.3 +/- 24.2 microM). The apparent Mg(2+) affinity constants of the MHS RyR1 A- and I-sites were approximately twice those of the A- and I-sites of the normal RyR1 (K(A,Mg): MHS = 44.36 +/- 4.54 microM; normal = 21.59 +/- 1.66 microM; K(I,Mg): MHS = 660.8 +/- 53.0 microM; normal = 299.2 +/- 24.5 microM). Thus, the reduced Mg(2+) inhibition of the MHS RyR1 compared with the normal RyR1 is due to both an enhanced selectivity of the MHS RyR1 A-site for Ca(2+) over Mg(2+) and a reduced Mg(2+) affinity of the I-site.
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Affiliation(s)
- E M Balog
- Department Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
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3
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Abstract
The quantitative effects of Ca(2+) signaling on gap junctional coupling in lens epithelial cells have been determined using either the spread of Mn(2+) that is imaged by its ability to quench the fluorescence of fura 2 or the spread of the fluorescent dye Alexa Fluor 594. Gap junctional coupling was unaffected by a mechanically stimulated cell-to-cell Ca(2+) wave. Furthermore, when cytosolic Ca(2+) concentration (Ca) increased after the addition of the agonist ATP, coupling was unaffected during the period that Ca was maximal. However, coupling decreased transiently approximately 5-10 min after agonist addition when Ca returned to resting levels, indicating that this transient decrease in coupling was unlikely due to a direct action of Ca on gap junctions. An increase in Ca mediated by the ionophore ionomycin that was sustained for several minutes resulted in a more rapid and sustained decrease in coupling (IC(50) ~300 nM Ca(2+), Hill coefficient of 4), indicating that an increase in Ca alone could regulate gap junctions. Thus Ca increases that occurred during agonist stimulation and cell-to-cell Ca(2+) waves were too transient to mediate a sustained uncoupling of lens epithelial cells.
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Affiliation(s)
- G C Churchill
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Abstract
The functional consequence of the casein kinase I-catalyzed phosphorylation of the lens gap junctional protein connexin49 was investigated using a sheep primary lens cell culture system. To determine whether the phosphorylation of connexin49 catalyzed by endogenous casein kinase I results in an altered junctional communication between lens cells, the effect of the casein kinase I-specific inhibitor CKI-7 on Lucifer Yellow dye transfer between cells in the lens culture was examined. Dye transfer was analyzed in cultures of different ages because we have demonstrated previously that the expression of connexin49 increases as the cultures age while that of connexin43, which is likely not a substrate for casein kinase I, has been shown to decrease [Yang & Louis (1999) Invest. Ophthalmol. Vis. Sci. 41: 2568-2564]. In 9-day old lens cultures, in which gap junctions are composed primarily of connexin43, CKI-7 had little effect on the rate of dye transfer between lens cells. In contrast, treatment of 15-day and 28-day old cultures with CKI-7 resulted in a significant increase in the rate of dye transfer. Thus, the extent of this CKI-7-dependent increase in cell-to-cell communication was positively correlated with the level of expression of connexin49, the major casein kinase I substrate in lens plasma membranes. These results suggest that the casein kinase I-catalyzed phosphorylation of connexin49 decreases cell communication between connexin49-containing gap junctions in the lens.
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Affiliation(s)
- H L Cheng
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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Zhao F, Li P, Chen SR, Louis CF, Fruen BR. Dantrolene inhibition of ryanodine receptor Ca2+ release channels. Molecular mechanism and isoform selectivity. J Biol Chem 2001; 276:13810-6. [PMID: 11278295 DOI: 10.1074/jbc.m006104200] [Citation(s) in RCA: 229] [Impact Index Per Article: 10.0] [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: 11/06/2022] Open
Abstract
As an inhibitor of Ca(2+) release through ryanodine receptor (RYR) channels, the skeletal muscle relaxant dantrolene has proven to be both a valuable experimental probe of intracellular Ca(2+) signaling and a lifesaving treatment for the pharmacogenetic disorder malignant hyperthermia. However, the molecular basis and specificity of the actions of dantrolene on RYR channels have remained in question. Here we utilize [(3)H]ryanodine binding to further investigate the actions of dantrolene on the three mammalian RYR isoforms. The inhibition of the pig skeletal muscle RYR1 by dantrolene (10 microm) was associated with a 3-fold increase in the K(d) of [(3)H]ryanodine binding to sarcoplasmic reticulum (SR) vesicles such that dantrolene effectively reversed the 3-fold decrease in the K(d) for [(3)H]ryanodine binding resulting from the malignant hyperthermia RYR1 Arg(615) --> Cys mutation. Dantrolene inhibition of the RYR1 was dependent on the presence of the adenine nucleotide and calmodulin and reflected a selective decrease in the apparent affinity of RYR1 activation sites for Ca(2+) relative to Mg(2+). In contrast to the RYR1 isoform, the cardiac RYR2 isoform was unaffected by dantrolene, both in native cardiac SR vesicles and when heterologously expressed in HEK-293 cells. By comparison, the RYR3 isoform expressed in HEK-293 cells was significantly inhibited by dantrolene, and the extent of RYR3 inhibition was similar to that displayed by the RYR1 in native SR vesicles. Our results thus indicate that both the RYR1 and the RYR3, but not the RYR2, may be targets for dantrolene inhibition in vivo.
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Affiliation(s)
- F Zhao
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis 55455, USA
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Abstract
Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle characterized by muscle contracture and life-threatening hypermetabolic crisis following exposure to halogenated anesthetics and depolarizing muscle relaxants during surgery. Susceptibility to MH results from mutations in Ca2+ channel proteins that mediate excitation-contraction (EC) coupling, with the ryanodine receptor Ca2+ release channel (RyRI) representing the major locus. Here we review recent studies characterizing the effects of MH mutations on the sensitivity of the RyRI to drugs and endogenous channel effectors including Ca2+ and calmodulin. In addition, we present a working model that incorporates these effects of MH mutations on the isolated RyRI with their effects on the physiologic mechanism that activates Ca2+ release during EC coupling in intact muscle.
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Affiliation(s)
- C F Louis
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis 55455, USA.
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Fruen BR, Bardy JM, Byrem TM, Strasburg GM, Louis CF. Differential Ca(2+) sensitivity of skeletal and cardiac muscle ryanodine receptors in the presence of calmodulin. Am J Physiol Cell Physiol 2000; 279:C724-33. [PMID: 10942723 DOI: 10.1152/ajpcell.2000.279.3.c724] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.2] [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]
Abstract
Calmodulin (CaM) activates the skeletal muscle ryanodine receptor Ca(2+) release channel (RyR1) in the presence of nanomolar Ca(2+) concentrations. However, the role of CaM activation in the mechanisms that control Ca(2+) release from the sarcoplasmic reticulum (SR) in skeletal muscle and in the heart remains unclear. In media that contained 100 nM Ca(2+), the rate of (45)Ca(2+) release from porcine skeletal muscle SR vesicles was increased approximately threefold in the presence of CaM (1 microM). In contrast, cardiac SR vesicle (45)Ca(2+) release was unaffected by CaM, suggesting that CaM activated the skeletal RyR1 but not the cardiac RyR2 channel isoform. The activation of RyR1 by CaM was associated with an approximately sixfold increase in the Ca(2+) sensitivity of [(3)H]ryanodine binding to skeletal muscle SR, whereas the Ca(2+) sensitivity of cardiac SR [(3)H]ryanodine binding was similar in the absence and presence of CaM. Cross-linking experiments identified both RyR1 and RyR2 as predominant CaM binding proteins in skeletal and cardiac SR, respectively, and [(35)S]CaM binding determinations further indicated comparable CaM binding to the two isoforms in the presence of micromolar Ca(2+). In nanomolar Ca(2+), however, the affinity and stoichiometry of RyR2 [(35)S]CaM binding was reduced compared with that of RyR1. Together, our results indicate that CaM activates RyR1 by increasing the Ca(2+) sensitivity of the channel, and further suggest differences in CaM's functional interactions with the RyR1 and RyR2 isoforms that may potentially contribute to differences in the Ca(2+) dependence of channel activation in skeletal and cardiac muscle.
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Affiliation(s)
- B R Fruen
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
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Yang DI, Louis CF. Molecular cloning of ovine connexin44 and temporal expression of gap junction proteins in a lens cell culture. Invest Ophthalmol Vis Sci 2000; 41:2658-64. [PMID: 10937579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
PURPOSE The lens plasma membranes of several mammalian species have been shown to contain three different connexin proteins. The goal of this study was to clone the sheep homologue of rat connexin46 identified as sheep connexin44 and to determine the temporal changes in the expression of the three sheep connexin proteins in a lens primary cell culture system. METHODS A sheep genomic library was screened with a rat lens connexin46 cDNA probe. Lens junctional protein and mRNA levels were determined in a sheep primary cell culture system by Western and Northern blot analyses, respectively. RESULTS Sheep connexin44, the homologue of rat lens connexin46, was identified as a single-copy gene with a predicted molecular weight of 43,989 Daltons that is contained within a single exon. Northern blot analysis detected a 2.2-kb connexin44 transcript in RNA isolated from lens but not that isolated from heart, kidney, liver, or lung. During the in vitro differentiation of lens epithelial cells from 5 to 20 days in culture, connexin43 mRNA levels declined approximately 75%, whereas connexin49 RNA levels increased approximately 24 fold. The 40% decrease in the level of connexin43 protein and the 21-fold increase in the level of connexin49 protein did not directly correlate with the changes in mRNA levels encoding these proteins during this same period. Although detectable, the amount of connexin44 mRNA and protein remained low throughout the 20-day period during which lens cells were grown in culture. Neither mRNA nor protein encoding MP20 or MP26 transcripts could be detected in even the oldest 20-day lens cultures. CONCLUSIONS Steady state mRNA levels of sheep connexin43 and connexin49 do not appear to be the only factor regulating the expression of these genes during in vitro differentiation of lens cells in culture. Although a decreased level of expression of connexin43 was accompanied by an increased level of expression of connexin49 over the 20-day period in culture, connexin44 mRNA and protein levels remained low throughout this 20-day period. Overall, these results suggest that these junctional proteins have a unique temporal pattern of expression during differentiation, and this lens primary cell culture system provides a valuable tool to better understand this process.
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Affiliation(s)
- D I Yang
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis 55455, USA
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Janzen MA, Kuhlers DL, Jungst SB, Louis CF. ARPP-16 mRNA is up-regulated in the longissimus muscle of pigs possessing an elevated growth rate. J Anim Sci 2000; 78:1475-84. [PMID: 10875629 DOI: 10.2527/2000.7861475x] [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: 11/13/2022] Open
Abstract
Selection for increased growth rate in farm and laboratory animals has been used to develop lines with increased body and muscle weights. However, very little is known about the underlying molecular pathways and how their constitutive genes influence this process. In this study, the differential display-reverse transcription PCR (DDRT-PCR) method was employed to identify longissimus muscle genes that are differentially expressed between a line of pigs selected for increased 200-d weight and a randomly selected control line. A 590-bp DDRT-PCR cDNA product was identified and isolated based on its greater abundance in the longissimus muscle of the select line relative to the control line animals. This DDRT-PCR product has 89% identity to the end of the 3'-untranslated region of the bovine 16-kDa cAMP-regulated phosphoprotein (ARPP-16) cDNA sequence. Reverse transcription PCR (RT-PCR) amplification of the porcine homologue of ARPP-16 and subsequent sequencing established that the DDRT-PCR product corresponds to the 3'-end of the porcine ARPP-16 transcript. Semiquantitative RT-PCR verified that ARPP-16 is up-regulated in the select line and determined that the relative expression level of ARPP16 mRNA is approximately fourfold higher (P < .01) in the select than in the control animals. The deduced amino acid sequence of ARPP-16 is highly homologous to the deduced amino acid sequences of bovine, human, and rat ARPP-16, and RT-PCR with ARPP-16-specific PCR primers indicated that this gene is expressed in many different porcine tissues. The porcine homologue of the 19-kDa cAMP-regulated phosphoprotein (ARPP-19) was also amplified by RT-PCR, cloned, and sequenced. The deduced amino acid sequence of ARPP19 differs from ARPP-16 only by the addition of 16 N-terminal amino acids. In all tissues studied, ARPP-19 mRNA was detected by RT-PCR amplification; however, the relative expression level of ARPP-19 mRNA was not differentially expressed between the select and control line animals (P > .05). The fourfold relative increase in ARPP-16 mRNA expression in the select line animals indicates that this gene may play an important role in the molecular pathway(s) that regulate postnatal skeletal muscle growth in the pig.
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Affiliation(s)
- M A Janzen
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota, Minneapolis, 55455, USA
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10
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Abstract
Inorganic phosphate (P(i)) accumulates in the fibers of actively working muscle where it acts at various sites to modulate contraction. To characterize the role of P(i) as a regulator of the sarcoplasmic reticulum (SR) calcium (Ca(2+)) release channel, we examined the action of P(i) on purified SR Ca(2+) release channels, isolated SR vesicles, and skinned skeletal muscle fibers. In single channel studies, addition of P(i) to the cis chamber increased single channel open probability (P(o); 0.079 +/- 0.020 in 0 P(i), 0. 157 +/- 0.034 in 20 mM P(i)) by decreasing mean channel closed time; mean channel open times were unaffected. In contrast, the ATP analog, beta,gamma-methyleneadenosine 5'-triphosphate (AMP-PCP), enhanced P(o) by increasing single channel open time and decreasing channel closed time. P(i) stimulation of [(3)H]ryanodine binding by SR vesicles was similar at all concentrations of AMP-PCP, suggesting P(i) and adenine nucleotides act via independent sites. In skinned muscle fibers, 40 mM P(i) enhanced Ca(2+)-induced Ca(2+) release, suggesting an in situ stimulation of the release channel by high concentrations of P(i). Our results support the hypothesis that P(i) may be an important endogenous modulator of the skeletal muscle SR Ca(2+) release channel under fatiguing conditions in vivo, acting via a mechanism distinct from adenine nucleotides.
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Affiliation(s)
- E M Balog
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, St. Paul, Minnesota 55455, USA.
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Affiliation(s)
- F Zhao
- Department of Biochemistry, University of Minnesota, Minneapolis 55455, USA
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Zhao F, Ambady S, Ponce de León FA, Miller LM, Lunney JK, Grimm DR, Schook LB, Louis CF. Microsatellite markers from a microdissected swine chromosome 6 genomic library. Anim Genet 1999; 30:251-5. [PMID: 10467699 DOI: 10.1046/j.1365-2052.1999.00502.x] [Citation(s) in RCA: 6] [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: 11/20/2022]
Abstract
To develop additional microsatellite (MS) markers in the region of the porcine skeletal muscle ryanodine receptor gene (RYR1), a microdissected genomic library was generated from the proximal half of the q arm of swine chromosome 6. Purified DNA was restriction enzyme-digested, ligated to oligonucleotide adaptors and amplified by PCR using primers complementary to the adaptor sequences. The purity of the amplified products and boundaries of the microdissected chromosomal region were verified by fluorescence in situ hybridization. (CA)n-containing sequences were then identified in a small insert genomic library generated from the PCR-amplified microdissected DNA. Oligonucleotide primers were developed for the PCR amplification of 30 of the 46 (CA)n repeat-containing clones, which were subsequently used to amplify DNA isolated from unrelated pigs of different breeds to determine the informativeness of these MS markers. Twenty-two of these MS markers were genotyped on the University of Illinois Yorkshire x Meishan swine reference population. These 22 markers were all assigned within a 50.7-CM region of the swine chromosome 6 linkage map, indicating the specificity of the microdissected library.
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Affiliation(s)
- F Zhao
- Department of Biochemistry, University of Minnesota, Minneapolis 55455, USA
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Abstract
The lens fiber cell-specific gap junction protein connexin49 is a substrate for a membrane-associated Ser/Thr protein kinase that can be extracted from lens cell membranes by 0.6 M KCl. However, the identity of this protein kinase has not been defined. In this report, evidence is presented indicating that it is casein kinase I. Thus, connexin49 was shown to be a substrate for purified casein kinase I but not for casein kinase II; the endogenous connexin49 protein kinase activity extracted from lens membranes with KCl was inhibited by the casein kinase I-specific inhibitor, N-(2-aminoethyl)-5-chloroisoquinoline-8-sulfonamide (CKI-7); the connexin49 protein kinase activity in the lens membrane KCl extract, which could be partially purified by gel filtration and affinity purification with a casein-Sepharose 4B column, copurified with casein kinase activity; phosphopeptide analysis showed that casein kinase I and the connexin49 protein kinase activity in the lens membrane KCl extract probably share the same phosphorylation sites in connexin49. Reverse transcription-PCR using total ovine lens RNA and casein kinase I isoform-specific oligonucleotide primers resulted in the amplification of cDNAs encoding casein kinase I-alpha and -gamma, while an in-gel casein kinase assay indicated casein kinase activity in the lens membrane KCl extract was associated with a major 39.2-kDa species, which is consistent with the 36 to 40-kDa size of casein kinase I-alpha in other animal species. These results demonstrate that the protein kinase activity present in the lens membrane 0.6 M KCl extract that catalyzes the phosphorylation of connexin49 is casein kinase I, probably the alpha isoform.
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Affiliation(s)
- H L Cheng
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN, USA
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Abstract
The centromeric region of swine chromosomes is comprised of tandemly repeated, divergent DNA monomer units. Here we report that these divergent DNA monomer sequences are organized into higher-order repeats, analogous to the hierarchical organization of alpha-satellite monomers in human centromeres. In this study, a centromeric cosmid clone was shown to be comprised entirely of a 3.3-kb higher-order repeat, with independent copies of this higher-order repeat more than 99% identical to each other. This higher-order repeat is composed of ten divergent monomer units of approximately 340 bp. The ten monomers are on average 79% identical, and all ten monomers are arranged in the same 5' to 3' orientation. In FISH analysis, a cloned 3.3-kb higher-order repeat hybridized to the centromere of Chromosome (Chr) 9 in metaphase spreads and detected two discrete foci in interphase nuclei, demonstrating that this swine higher-order repeat is chromosome-specific. The Chr 9 centromeric array spanned approximately 2.2 Mb as determined by pulsed-field gel electrophoresis. Moreover, the swine Chr 9 centromere is highly polymorphic, because an EcoRI restriction site polymorphism was detected. Thus, the assembly of divergent satellite sequences into chromosome-specific higher-order repeats appears to be a common organizational feature of both the human and swine centromere and suggests that the evolutionary mechanism(s) that create and maintain higher-order repeats is conserved between their genomes.
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Affiliation(s)
- M A Janzen
- Department of Biochemistry, University of Minnesota, St. Paul, Minnesota 55108, USA
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Abstract
Intracellular Ca2+ stores in permeabilized sheep lens cells were imaged with mag-fura 2 to characterize their distribution and sensitivity to Ca2+-releasing agents. Inositol 1,4,5-trisphosphate (IP3) or cyclic ADP-ribose (cADPR) released Ca2+ from intracellular Ca2+ stores that were maintained by an ATP-dependent Ca2+ pump. The IP3 antagonist heparin inhibited IP3- but not cADPR-mediated Ca2+ release, whereas the cADPR antagonist 8-amino-cADPR inhibited cADPR- but not IP3-mediated Ca2+ release, indicating that IP3 and cADPR were operating through separate mechanisms. A Ca2+ store sensitive to IP3, cADPR, and thapsigargin appeared to be distributed throughout all intracellular regions. In some cells a Ca2+ store insensitive to IP3, cADPR, thapsigargin, and 2,4-dinitrophenol, but not ionomycin, was present in a juxtanuclear region. We conclude that lens cells contain intracellular Ca2+ stores that are sensitive to IP3, cADPR, and thapsigargin, as well as a Ca2+ store that appears insensitive to all these agents.
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Affiliation(s)
- G C Churchill
- Department of Biochemistry, University of Minnesota, St. Paul, Minnesota 55108, USA
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Churchill GC, Louis CF. Roles of Ca2+, inositol trisphosphate and cyclic ADP-ribose in mediating intercellular Ca2+ signaling in sheep lens cells. J Cell Sci 1998; 111 ( Pt 9):1217-25. [PMID: 9547298 DOI: 10.1242/jcs.111.9.1217] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [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: 11/20/2022] Open
Abstract
To further characterize how gap junction-dependent Ca2+ waves propagate between sheep lens cells, we examined the possible roles of inositol 1,4,5-trisphosphate (IP3), Ca2+ and cyclic ADP-ribose (cADPR) in mediating intercellular Ca2+ waves. Second messengers were microinjected into a single cell in a monolayer of sheep lens cells while monitoring cytosolic Ca2+ with fura-2 and fluorescence microscopy. All three compounds initiated intercellular Ca2+ waves, but more cells responded following the injection of either IP3 or cADPR than responded following the injection of Ca2+. When either IP3 or cADPR was co-injected with the Ca2+ chelator EGTA, cytosolic Ca2+ in the injected cell decreased but cytosolic Ca2+ in the adjacent cells increased, indicating that the intercellular messenger was IP3 or cADPR, rather than Ca2+. The phospholipase C inhibitor U73122 eliminated mechanically initiated intercellular Ca2+ waves, indicating that mechanical initiation probably requires IP3 production. In U73122-treated cells, injected IP3 initiated an intercellular Ca2+ wave in which the number of cells responding increased as the amount of IP3 injected increased, indicating that the distance traveled by the Ca2+ wave was dependent on cell-to-cell diffusion of IP3. In contrast, the ability of cADPR both to increase cytosolic Ca2+ in the injected cell and to initiate intercellular Ca2+ waves was greatly attenuated by U73122. In conclusion, Ca2+, IP3 and cADPR can all mediate intercellular Ca2+ waves by passing through gap junction channels, but both IP3 and cADPR are more effective intercellular messengers than Ca2+.
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Affiliation(s)
- G C Churchill
- Department of Biochemistry, University of Minnesota, St. Paul, MN 55108, USA
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Abstract
The membrane topology of the bovine lens fiber cell plasma membrane protein MP20 has been examined using anti-peptide antibodies and the hydrophobic label 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazerine ([125I]TID). The specificity of the affinity-purified anti-peptide polyclonal antibodies, directed against four separate hydrophilic segments of MP20, was established by immunodot blots, Western immunoblotting and ELISA. Western immunodetection of protease-treated, urea-washed lens membranes indicated that each of the segments of MP20 identified by the anti-peptide antibodies was accessible to proteases indicating their likely extramembranous location. Immunoelectron microscopy of junctional lens membrane immunolabeled with MP20 anti-peptide antibodies directed against two segments predicted to be on the extra-cellular face of the lens fiber cell plasma membrane suggests these segments may actually be located on the cytoplasmic plasma membrane face. Transmembrane segments of MP20, identified using the hydrophotic photo-affinity label [125I]TID, were isolated and sequenced. Only three of the four previously proposed transmembrane segments of this protein were significantly labeled with this reagent. Based on these results and previously reported information regarding MP20, a new topological model is proposed for the arrangement of MP20 in the lens fiber cell plasma membrane. The new topological model of MP20 includes two alpha-helical and two beta-strand transmembrane segments.
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Affiliation(s)
- M L Arneson
- Department of Biochemistry, University of Minnesota, St Paul, MN 55108, USA
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Janzen MA, Alexander LJ, Rohrer GA, Beattie CW, Buoen LB, Louis CF. Physical assignment of two porcine cosmid clones containing polymorphic microsatellites. Anim Genet 1998; 29:70-1. [PMID: 9682464] [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: 02/08/2023]
Affiliation(s)
- M A Janzen
- Department of Biochemistry, University of Minnesota, St Paul 55108, USA
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Abstract
To better understand the altered skeletal muscle excitation-contraction (E-C) coupling that occurs in malignant hyperthermia, we have examined the potentiating actions of perchlorate in intact muscle fiber bundles, isolated sarcoplasmic reticulum (SR) vesicles, and the purified ryanodine receptor/Ca2+ release channel (RyR) isolated from malignant-hyperthermia-susceptible (MHS) and normal porcine muscle. The concentration of perchlorate that half-maximally potentiated twitch tension (2.5-3.5 mM) was not significantly different for MHS and normal muscles. The effect of perchlorate on fractional twitch force was significantly greater for normal than for MHS muscle, although the absolute twitch potentiation was similar for both muscle types. The K-contracture threshold of MHS muscle bundles is significantly lower than that of normal bundles; perchlorate shifted the K-contraction activation curves of both MHS and normal muscle bundles to lower K+ concentrations. Perchlorate both increased ryanodine binding to MHS and normal SR vesicles and increased single-channel open probability of the purified MHS and normal RyR. In both cases, the percentage increase was greater for normal than for MHS preparations; however, the absolute increase in activity was not different for MHS and normal RyR indicating that there is no difference in the perchlorate sensitivity of MHS and normal SR Ca2+ release channels. Thus, the greater absolute responses of the MHS Ca2+ release channel in the presence of perchlorate is likely to be due to the greater basal activity of the MHS release channel and does not reflect an underlying defect in the site of action of perchlorate on the MHS skeletal muscle Ca2+ release channel.
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Affiliation(s)
- L C Anderson
- Department of Veterinary PathoBiology, University of Minnesota, 1988 Fitch Avenue, Room 295, St. Paul, MN 55108, USA
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Tenbroek EM, Louis CF, Johnson R. The differential effects of 12-O-tetradecanoylphorbol-13-acetate on the gap junctions and connexins of the developing mammalian lens. Dev Biol 1997; 191:88-102. [PMID: 9356174 DOI: 10.1006/dbio.1997.8703] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [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: 02/05/2023]
Abstract
Epithelial cells in primary ovine lens cultures express the gap junction proteins connexin43 (Cx43) and connexin49 (Cx49; a.k.a. MP70), a homologue of mouse connexin50. In contrast, lens cultures of differentiated, fiber-like cells (termed lentoid cells) express Cx49 and connexin46 (Cx46), but not Cx43. To investigate the regulation of lens cell gap junctions by protein kinase C (PKC), differentiating lens cultures were treated with the PKC activator 12-O-tetradecanoylphorbol-13-acetate (beta-TPA). Within 10 min, beta-TPA significantly inhibited the transfer of Lucifer Yellow dye between epithelial, but not lentoid, cells. This inhibition was correlated with the phosphorylation of Cx43 and was followed by the gradual disappearance of Cx43 from cell interfaces. The protein kinase inhibitor staurosporine prevented Cx43 phosphorylation and the loss of Cx43 from intercellular junctions. Following treatment of cultures with beta-TPA for 2-6 hr, Cx49 disappeared from epithelial cell interfaces, and by 24 hr of beta-TPA treatment, levels of Cx49 detected on immunoblots of purified epithelial membrane fractions had also diminished significantly. The beta-TPA-induced loss of Cx49 both from regions of epithelial cell contact and from isolated membranes was correlated with the disappearance of Cx49 mRNA. In contrast to the epithelial connexins, the lentoid connexins Cx49 and Cx46 were unaffected by even extended beta-TPA treatment. In spite of lentoid dye transfer being refractory to beta-TPA, significant levels of PKC-alpha (a beta-TPA-sensitive isoform) were detected in the lentoid cell. The response of lens gap junctions to beta-TPA depends upon the stage of differentiation and the complement of connexins expressed. The contrasting effects of beta-TPA on Cx43 and Cx49 in lens epithelial cells indicate a fundamental difference in the regulation of these connexin proteins in the developing mammalian lens.
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Affiliation(s)
- E M Tenbroek
- Department of Genetics and Cell Biology, University of Minnesota, St. Paul, Minnesota 55108, USA
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21
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Fruen BR, Mickelson JR, Louis CF. Dantrolene inhibition of sarcoplasmic reticulum Ca2+ release by direct and specific action at skeletal muscle ryanodine receptors. J Biol Chem 1997; 272:26965-71. [PMID: 9341133 DOI: 10.1074/jbc.272.43.26965] [Citation(s) in RCA: 156] [Impact Index Per Article: 5.8] [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: 02/05/2023] Open
Abstract
The skeletal muscle relaxant dantrolene inhibits the release of Ca2+ from the sarcoplasmic reticulum during excitation-contraction coupling and suppresses the uncontrolled Ca2+ release that underlies the skeletal muscle pharmacogenetic disorder malignant hyperthermia; however, the molecular mechanism by which dantrolene selectively affects skeletal muscle Ca2+ regulation remains to be defined. Here we provide evidence of a high-affinity, monophasic inhibition by dantrolene of ryanodine receptor Ca2+ channel function in isolated sarcoplasmic reticulum vesicles prepared from malignant hyperthermia-susceptible and normal pig skeletal muscle. In media simulating resting myoplasm, dantrolene increased the half-time for 45Ca2+ release from both malignant hyperthermia and normal vesicles approximately 3.5-fold and inhibited sarcoplasmic reticulum vesicle [3H]ryanodine binding (Ki approximately 150 nM for both malignant hyperthermia and normal). Inhibition of vesicle [3H]ryanodine binding by dantrolene was associated with a decrease in the extent of activation by both calmodulin and Ca2+. Dantrolene also inhibited [3H]ryanodine binding to purified skeletal muscle ryanodine receptor protein reconstituted into liposomes. In contrast, cardiac sarcoplasmic reticulum vesicle 45Ca2+ release and [3H]ryanodine binding were unaffected by dantrolene. Together, these results demonstrate selective effects of dantrolene on skeletal muscle ryanodine receptors that are consistent with the actions of dantrolene in vivo and suggest a mechanism of action in which dantrolene may act directly at the skeletal muscle ryanodine receptor complex to limit its activation by calmodulin and Ca2+. The potential implications of these results for understanding how dantrolene and malignant hyperthermia mutations may affect the voltage-dependent activation of Ca2+ release in intact skeletal muscle are discussed.
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Affiliation(s)
- B R Fruen
- Departments of Veterinary PathoBiology, University of Minnesota, St. Paul, Minnesota 55108, USA
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22
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Palnitkar SS, Mickelson JR, Louis CF, Parness J. Pharmacological distinction between dantrolene and ryanodine binding sites: evidence from normal and malignant hyperthermia-susceptible porcine skeletal muscle. Biochem J 1997; 326 ( Pt 3):847-52. [PMID: 9307036 PMCID: PMC1218741 DOI: 10.1042/bj3260847] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [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: 02/05/2023]
Abstract
Dantrolene inhibits and ryanodine stimulates calcium release from skeletal-muscle sarcoplasmic reticulum (SR), the former by an unknown mechanism, and the latter by activating the ryanodine receptor (RyR), the primary Ca2+-release channel of SR. Dantrolene is used to treat malignant hyperthermia (MH), a genetic predisposition to excessive intracellular Ca2+ release upon exposure to volatile anaesthetics. Porcine MH results from a point mutation in the SR RyR that alters the open probability of the channel, and is reflected in altered [3H]ryanodine binding parameters. Specific binding sites for [3H]dantrolene and [3H]ryanodine co-distribute on SR that has been isolated by discontinuous sucrose gradient centrifugation. If the two drug-binding sites are functionally linked, [3H]dantrolene binding might be affected both by pharmacological and by genetic modulators of the functional state of the RyR. Accordingly, we compared the characteristics of [3H]dantrolene binding to porcine malignant-hyperthermia-susceptible and normal-skeletal-muscle SR, and examined the effects of RyR modulators on [3H]dantrolene binding to these membranes. Additionally, the feasibility of separating the SR binding sites for [3H]dantrolene and [3H]ryanodine was investigated. No significant differences in [3H]dantrolene binding characteristics to SR membranes from the two muscle types were detected, and the Bmax ratio for [3H]dantrolene/[3H]ryanodine was 1.4(+/-0.1):1 in both muscle types. [3H]Dantrolene binding is unaffected by the RyR modulators caffeine, ryanodine, Ruthenium Red and calmodulin, and neither dantrolene nor azumolene have any effect on [3H]ryanodine binding. Additionally, distinct peaks of [3H]dantrolene and [3H]ryanodine binding are detected in SR membranes fractionated by linear sucrose centrifugation, although no differences in protein patterns are detected by SDS/PAGE or Western-blot analysis. We suggest that the binding sites for these two drugs are pharmacologically distinct, and may exist on separate molecules.
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Affiliation(s)
- S S Palnitkar
- Department of Anesthesia, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick, NJ 08901, USA
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23
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Churchill GC, Louis CF. Stimulation of P2U purinergic or alpha 1A adrenergic receptors mobilizes Ca2+ in lens cells. Invest Ophthalmol Vis Sci 1997; 38:855-65. [PMID: 9112981] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
PURPOSE To identify agonists that elevate cytosolic Ca2+ (Cai2+) in lens cells and to characterize their mechanism of action. METHODS Digital imaging and the Ca(2+)-reporting dye fura-2 were used to study the effects of agonists and their antagonists of Cai2+ in sheep lens primary cell cultures. RESULTS Exposing cells to adenosine triphosphate (ATP) and epinephrine increased Cai2+, whereas dopamine, 5-hydroxytryptamine, acetylcholine, histamine, kassinin, bradykinin, and glutamate did not elevate Cai2+. The ATP response was mediated by P2U purinergic receptors based on inhibition by the P2 antagonist suramin and the agonist rank potency order ATP = UTP = ATP gamma S > ADP > AMP > > adenosine; adenine, AMP-CPP, and AMP-PCP were inactive. The epinephrine response was mediated by alpha 1 adrenergic receptors based on the greater potency of the alpha 1 adrenergic selective antagonist prazosin compared to that of the alpha 2 adrenergic selective antagonist yohimbine. More specifically, the epinephrine response was mediated by the alpha 1A adrenergic receptor subtype based on the greater potencies exhibited by the alpha 1A subtype selective competitive antagonists WB 4101 and 5-methylurapidil compared to the alpha 1B and alpha 1D selective antagonists spiperone and BMY 7378, respectively. The agonist-mediated Cai2+ increase was dependent on intracellular Ca2+ stores and was inhibited by the phospholipase C inhibitor U73122. ATP or epinephrine could desensitize the cells to either agonist because of both the depletion of intracellular Ca2+ stores and the downregulation of a common intermediate in the signal transduction pathway. CONCLUSIONS Ca2+ is mobilized from intracellular stores in the sheep lens by ATP and epinephrine acting through P2U purinergic and the alpha 1A adrenergic receptors, respectively. This confirms previous reports of P2U receptors in lens and provides the first report of alpha 1A adrenergic receptors in the lens.
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Affiliation(s)
- G C Churchill
- Department of Biochemistry, University of Minnesota, St. Paul 55108, USA
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24
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Ambady S, Mendiola JR, Louis CF, Janzen MA, Schook LB, Buoen L, Lunney JK, Grimm DR, Ponce de León FA. Development and use of a microdissected swine chromosome 6 DNA library. Cytogenet Cell Genet 1997; 76:27-33. [PMID: 9154119 DOI: 10.1159/000134506] [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] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
To facilitate the identification of microsatellite genetic markers from a single swine chromosome, chromosome microisolation and microcloning have been used to generate a swine chromosome 6-specific DNA library. Ten copies of swine chromosome 6 were scraped from metaphase spreads, ligated to custom-prepared adaptors, and amplified by PCR. The purity of the amplified product was verified by fluorescent in situ hybridization. The utility of the chromosome painting probe for heterologous painting was demonstrated and confirmed that swine chromosome 6 is syntenic to human chromosomes 1p and 19q. A small insert genomic library of 1.39 x 10(6) clones was generated from the PCR-amplified chromosome 6 genomic DNA and screened for (GT)n microsatellite genetic markers. Nine (GT)n microsatellite markers were developed and genotyped on a Yorkshire x Meishan swine reference family. All nine markers genetically mapped to chromosome 6, confirming the purity of the microisolation method. The method used here should be adaptable to the microdissection of subchromosomal regions of not only the swine genome but also other livestock genomes.
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Affiliation(s)
- S Ambady
- Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, USA
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25
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Fruen BR, Kane PK, Mickelson JR, Louis CF. Chloride-dependent sarcoplasmic reticulum Ca2+ release correlates with increased Ca2+ activation of ryanodine receptors. Biophys J 1996; 71:2522-30. [PMID: 8913591 PMCID: PMC1233740 DOI: 10.1016/s0006-3495(96)79445-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [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: 02/03/2023] Open
Abstract
The mechanism by which chloride increases sarcoplasmic reticulum (SR) Ca2+ permeability was investigated. In the presence of 3 microM Ca2+, Ca2+ release from 45Ca(2+)-loaded SR vesicles prepared from procine skeletal muscle was increased approximately 4-fold when the media contained 150 mM chloride versus 150 mM propionate, whereas in the presence of 30 nM Ca2+, Ca2+ release was similar in the chloride- and the propionate-containing media. Ca(2+)-activated [3H]ryanodine binding to skeletal muscle SR was also increased (2- to 10-fold) in media in which propionate or other organic anions were replaced with chloride; however, chloride had little or no effect on cardiac muscle SR 45Ca2+ release or [3H]ryanodine binding. Ca(2+)-activated [3H]ryanodine binding was increased approximately 4.5-fold after reconstitution of skeletal muscle RYR protein into liposomes, and [3H]ryanodine binding to reconstituted RYR protein was similar in chloride- and propionate-containing media, suggesting that the sensitivity of the RYR protein to changes in the anionic composition of the media may be diminished upon reconstitution. Together, our results demonstrate a close correlation between chloride-dependent increases in SR Ca2+ permeability and increased Ca2+ activation of skeletal muscle RYR channels. We postulate that media containing supraphysiological concentrations of chloride or other inorganic anions may enhance skeletal muscle RYR activity by favoring a conformational state of the channel that exhibits increased activation by Ca2+ in comparison to the Ca2+ activation exhibited by this channel in native membranes in the presence of physiological chloride (< or = 10 mM). Transitions to this putative Ca(2+)-activatable state may thus provide a mechanism for controlling the activation of RYR channels in skeletal muscle.
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Affiliation(s)
- B R Fruen
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108, USA.
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26
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Abstract
Malignant hyperthermia (MH) is a disorder of skeletal muscle in which certain anesthetic agents trigger a sustained elevation in myoplasmic Ca2+ concentration that activates metabolic and contractile activity. This review focuses on the biochemical and physiological alterations in the skeletal muscle of MH-susceptible (MHS) pigs and humans that appear responsible for this inherited disorder. In porcine MH, these studies identified the skeletal muscle sarcoplasmic reticulum Ca2+ release channel gene (RYR1) as the site of the defect. A mutation in this protein results in altered excitation-contraction coupling and secondary changes in porcine muscle structure and function. Although RYR1 mutations have been reported in many MHS human families, there is also significant genetic heterogeneity, and much less is known as to the underlying mechanism responsible for altered human myoplasmic Ca2+ regulation. The effects of caffeine and anesthetic agents on MHS and normal muscle are also discussed to better understand the basis for the in vitro clinical test for this disorder and mechanisms responsible for the initiation and maintenance of MH episodes in susceptible individuals. Finally, we examine the possiblity of a defect in Ca2+ regulation in tissues other than skeletal muscle. Current understanding of the molecular basis of MH elegantly illustrates the successful integration of knowledge obtained from all fields of biological and clinical science.
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Affiliation(s)
- J R Mickelson
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul, USA
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27
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Abstract
The nucleotide sequence of the sheep homologue of the lens-specific mouse connexin50, chicken connexin45.6, and human connexin50 has been obtained following screening of a sheep genomic library. This connexin comprises 1323 nucleotides, coding for a protein of 440 amino acid residues and a predicted molecular weight of 49,160 daltons, so by convention is termed sheep connexin49. A connexin49 cDNA probe detected a single major band with a mobility of 6.8 kb in sheep lens RNA, but not in RNA isolated from five other sheep organs. The N-terminal amino acid sequence of sheep connexin49 is identical to that of mouse connexin50 and closely matches that of MP70, indicating the identity of sheep connexin49 with MP70. The nucleotide and translated amino acid sequences of connexin49 have 69-87% and 76%-87% identity respectively with chicken connexin45.6, human connexin50 and mouse connexin50. Like other members of this lens connexin family, sheep connexin49 coding region is completely contained within one exon, and the sequence of the N-terminal region, the four transmembrane domains and the two extracellular loops are highly conserved.
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Affiliation(s)
- D I Yang
- Department of Biochemistry, University of Minnesota, St Paul 55108, USA
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28
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Abstract
Although abnormalities in calcium regulation have been implicated in the development of most forms of cataract, the mechanisms by which Ca2+ is regulated in the cells of the ocular lens remain poorly defined. Cell-to-cell Ca2+ signaling was investigated in primary cultures of ovine epithelial cells using the Ca(2+)-reporter dye fura-2 and fluorescence microscopy. Mechanical stimulation of a single cell with a micropipette initiated a propagated increase in cytosolic free Ca2+ that spread from the stimulated cell through 2–8 tiers of surrounding cells. During this intercellular Ca2+ wave, cytosolic Ca2+ increased 2- to 12-fold from resting levels of approximately 100 nM. Nanomolar extracellular Ca2+ did not affect the cell-to-cell propagation of the Ca2+ wave, but reduced the magnitude of the cytosolic Ca2+ increases, which was most evident in the mechanically-stimulated cell. Depletion of intracellular Ca2+ stores with thapsigargin eliminated the propagated intercellular Ca2+ wave, but did not prevent the cytosolic Ca2+ increase in the mechanically-stimulated cell, which required extracellular Ca2+ and was attenuated by the addition of the Ca2+ channel blockers Ni2+, Gd3+ and La3+ to the medium. These results are most easily explained by a mechanically-activated channel in the plasma membrane of the stimulated cell. The propagated increase in cytosolic Ca2+ appeared to be communicated to adjacent cells by the passage of an intracellular messenger other than Ca2+ through gap junction channels. However, if the plasma membrane of the mechanically-stimulated cell was ruptured such that there was loss of cytosolic contents, the increase in cytosolic Ca2+ in the surrounding cells was elicited by both a messenger passing through gap junction channels and by a cytosolic factor(s) diffusing through the extracellular medium. These results demonstrate the existence of intercellular Ca2+ signaling in lens cells, which may play a role in regulating cytosolic Ca2+ in the intact lens.
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Affiliation(s)
- G C Churchill
- Department of Biochemistry, University of Minnesota, St Paul 55108, USA
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29
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Abstract
The cAMP-dependent protein-kinase-catalyzed phosphorylation of the two major intrinsic lens fiber cell plasma membrane proteins, MP20 and MP26, is likely restricted to the inner cortical and nuclear regions of the lens in vivo. The ovine-lens-specific connexin, MP70, that has been identified as Cx50 in mice and Cx45.6 in the chick, is also a protein kinase substrate although it does not appear to be phosphorylated by a number of protein kinases including cAMP-dependent protein kinase, calmodulin-dependent protein kinase or protein kinase C. Rather, an extrinsic lens membrane fraction was isolated which contained protein kinase activity that catalyzed the phosphorylation of MP70; this protein kinase activity was cAMP-independent, Ca(2+)-independent, Mg(2+)-dependent, phosphorylated MP70 on a serine residue(s) and migrated with a molecular mass of 35 kDa on a gel filtration column. Both MP70 phosphorylation and the endogenous protein kinase activity were restricted to the lens outer cortical region. This membrane-associated protein kinase activity represents the first reported partial characterization of an endogenous lens fiber cell protein kinase activity that catalyzes the phosphorylation of a lens connexin protein. The phosphatase-induced shift in the electrophoretic mobility of MP70 is not reversed by this protein kinase, indicating that MP70 is likely phosphorylated on different residues by two or more protein kinases.
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Affiliation(s)
- M L Arneson
- Department of Biochemistry, University of Minnesota, St Paul 55108, USA
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30
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Paszek AA, Schook LB, Louis CF, Mickelson JR, Flickinger GH, Murtaugh J, Mendiola JR, Janzen MA, Beattie CW, Rohrer GA. First international workshop on porcine chromosome 6. Report and abstracts. Anim Genet 1995; 26:377-401. [PMID: 8572361 DOI: 10.1111/j.1365-2052.1995.tb02689.x] [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: 01/31/2023]
Abstract
Recent advances in the use of microsatellite markers and the development of comparative gene mapping techniques have made the construction of high resolution genetic maps of livestock species possible. Framework and comprehensive genetic linkage maps of porcine chromosome 6 have resulted from the first international effort to integrate genetic maps from multiple laboratories. Eleven highly polymorphic genetic markers were exchanged and mapped by four independent laboratories on a total of 583 animals derived from four reference populations. The chromosome 6 framework map consists of 10 markers ordered with high local support. The average marker interval of the framework map is 15.1 cM (sex averaged). The framework map is 135, 175 and 109 cM in length (for sex averaged, female and male maps, respectively). The comprehensive map includes a total of 48 type I and type II markers with a sex averaged interval of 3.5 cM and is 166, 196 and 126 cM (for sex averaged, female and male maps, respectively). Additional markers within framework map marker intervals can thus be selected from the comprehensive map for further analysis of quantitive trait loci (QTL) located on chromosome 6. The resulting maps of swine chromosome 6 provide a valuable tool for analysing and locating QTL.
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Affiliation(s)
- A A Paszek
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 5108, USA
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31
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Lee JW, Zhang Y, Weaver CD, Shomer NH, Louis CF, Roberts DM. Phosphorylation of nodulin 26 on serine 262 affects its voltage-sensitive channel activity in planar lipid bilayers. J Biol Chem 1995; 270:27051-7. [PMID: 7592955 DOI: 10.1074/jbc.270.45.27051] [Citation(s) in RCA: 39] [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: 01/26/2023] Open
Abstract
Nodulin 26 is an symbiosome membrane protein of soybean nodules that shows ion channel activity in planar lipid bilayers. Serine 262 of nodulin 26 is phosphorylated by calmodulin-like domain protein kinase. To study the effects of phosphorylation, nodulin 26 with Ser, Ala, or Asp at position 262 were expressed in Escherichia coli. The expressed protein possessed a histidine-rich leader sequence for purification by Ni2+ chelate fast protein liquid chromatography. Upon reconstitution into planar lipid bilayers, the recombinant proteins showed a large single channel conductance (3.1 nanosiemens (nS) in cis0.2M/trans1.0 M KCl and 1.6 nS in cis 0.2M/trans0.2 M KCl) and weak anion selectivity, similar to native soybean nodulin 26. Nodulin 26 with Ser- or Ala-262 occupied the maximal open conductance state greater than 97% of the time (3.1 nS in cis0.2M/trans1.0 M KCl) regardless of applied voltage. However, nodulin 26 with Asp-262 showed increased gating and preferential occupancy of lower subconductance states (1.8 and 0.6 nS in cis0.2M/trans1.0 M KCl) at high applied voltages (e.g. 70 mV). In situ phosphorylation of Ser-262 of nodulin 26 by calmodulin-like domain protein kinase also resulted in increased voltage-dependent gating and preferential occupancy of lower subconductance states. These results suggest that phosphorylation of serine 262 of nodulin 26 modulates channel activity by conferring voltage sensitivity.
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Affiliation(s)
- J W Lee
- Department of Biochemistry, University of Tennessee, Knoxville 37996, USA
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32
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Abstract
Porcine malignant hyperthermia (MH) is an autosomal recessive disorder resulting from a mutation in the skeletal muscle sarcoplasmic reticulum (SR) Ca2+ release channel. The Ca2+ release properties of SR vesicles isolated from pigs heterozygous for the MH gene have been demonstrated previously to be intermediate to those of vesicles isolated from MH-susceptible (MHS) and normal pigs. The Ca2+ release channel is tetrameric, so the intermediate Ca2+ release properties of heterozygous pig SR preparations could result either from populations of MHS and normal homotetramers, or populations of heterotetrameric Ca2+ release channels with properties unique from those of the two types of homozygous channels. To discriminate between these possibilities, the single channel percent open time (Po) and channel dwell time distributions of SR Ca2+ release channels were analyzed. These data suggest that the heterozygous porcine Ca2+ release channel population must contain heterotetramers with properties distinct from those of either MHS or normal channels. The data also imply that the Ca2+ release channel population in MHS humans who are heterozygous for a dominant mutation in this protein also contains heterotetrameric channels.
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Affiliation(s)
- N H Shomer
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108, USA
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33
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Smith TP, Rohrer GA, Alexander LJ, Troyer DL, Kirby-Dobbels KR, Janzen MA, Cornwell DL, Louis CF, Schook LB, Beattie CW. Directed integration of the physical and genetic linkage maps of swine chromosome 7 reveals that the SLA spans the centromere. Genome Res 1995; 5:259-71. [PMID: 8593613 DOI: 10.1101/gr.5.3.259] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.9] [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: 01/31/2023]
Abstract
The first integrated physical and genetic linkage map encompassing the entire swine chromosome 7 (SSC7) reveals that the porcine MHC (SLA) spans the centromere. A SLA class II antigen gene lies on the q arm, whereas class I and III genes lie on the p arm, suggesting that the presence of a centromere within the SLA does not preclude a functional complex. The SLA appears smaller than other mammalian MHC, as the genetic distance across two class I, three class II, and three class III SLA gene markers is only 1.1 cM. There are significant variations in recombination rates as a function of position along the chromosome, and the SLA lies in the region with the lowest rate. Furthermore, the directed integration approach used in this study was more efficient than previous efforts that emphasized the screening of large insert libraries for random microsatellites.
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Affiliation(s)
- T P Smith
- U.S. Department of Agriculture (USDA), Roman L. Hruska U.S. Meat Animal Research Center (MARC), Clay Center, Nebraska 68933, USA.
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34
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Abstract
Purification of the lens fiber cell membrane proteins MP20 and MP26, and the partial co-purification of the lens connexin-related proteins MP70 and connexin 46 has been achieved using anion- and cation-exchange chromatography of lens fiber cell membrane proteins solubilized in n-octyl-beta-D-glucopyranoside (octyl glucoside). The apparent molecular weights of the solubilized protein-detergent complexes were significantly greater than that expected for the monomeric proteins. The purified proteins retained their ability to be phosphorylated by cAMP-dependent protein kinase, and to bind calmodulin in a calcium and magnesium dependent manner. The heterobifunctional covalent chemical crosslinking agent N-5-azido-2-nitro-benzoyloxysuccinimide (ANB-NOS), and the thiol oxidant cupric phenanthroline were used to identify the oligomeric states of these proteins. Crosslinking of either the purified proteins or native lens membranes generated a ladder of crosslinked MP20 or MP26 homo-oligomers. The largest detectable crosslinked homo-oligomer of MP20 was at least a hexamer, while for MP26 the largest crosslinked homo-oligomer was at least a tetramer. The possible oligomeric states of MP70 and connexin 46 could not be determined with the crosslinking reagents used in this study. The procedure described here for the purification of detergent-solubilized major lens proteins should provide a valuable approach in future studies aimed at clarifying the roles of these different lens membrane proteins.
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Affiliation(s)
- L J Jarvis
- Department of Biochemistry, University of Minnesota, St Paul 55108, USA
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35
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el-Hayek R, Yano M, Antoniu B, Mickelson JR, Louis CF, Ikemoto N. Altered E-C coupling in triads isolated from malignant hyperthermia-susceptible porcine muscle. Am J Physiol 1995; 268:C1381-6. [PMID: 7611356 DOI: 10.1152/ajpcell.1995.268.6.c1381] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Triad vesicles were isolated from normal (N) and homozygous malignant hyperthermia-susceptible (MHS) porcine skeletal muscle, and two types of sarcoplasmic reticulum Ca2+ release were investigated: 1) polylysine-induced Ca2+ release (direct stimulation of the junctional foot protein), and 2) depolarization-induced Ca2+ release (stimulation of the junctional foot protein via the dihydropyridine receptor). At submaximal concentrations of polylysine, the rates of induced Ca2+ release from the MHS triads were greater than from normal triads. The T tubules of polarized triads were depolarized by the K(+)-to-Na+ ionic replacement protocol. Higher grades of T-tubule depolarization resulted in higher rates of Ca2+ release from both MHS and normal triads but, when compared at a given grade of T-tubule depolarization, the release rate was always greater from the MHS than from normal triads. Thus the activity of the SR Ca2+ release channel is always higher in MHS than in normal muscle at a given submaximal dose of release trigger. This difference is observed when the channel is stimulated directly by polylysine or indirectly via a depolarization-induced activation of the T-tubule dihydropyridine receptor.
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Affiliation(s)
- R el-Hayek
- Department of Veterinary Biology, University of Minnesota, St. Paul 55108, USA
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Fruen BR, Kane PK, Mickelson JR, Louis CF. METABOLIC BY-PRODUCTS OF EXERCISE REGULATE THE SARCOPLASMIC RETICULUM Ca2+ RELEASE CHANNEL. Med Sci Sports Exerc 1995. [DOI: 10.1249/00005768-199505001-00795] [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: 11/21/2022]
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Abstract
BACKGROUND The effects of inhalation anesthetics on Ca2+ regulation in malignant hyperthermia-susceptible skeletal muscle are considered to be responsible for triggering malignant hyperthermia. The intravenous anesthetic propofol does not trigger malignant hyperthermia in susceptible patients or experimental animals, suggesting that there are important differences between the effects of propofol and the effects of inhalation anesthetics on Ca2+ regulation in malignant hyperthermia-susceptible muscle. Understanding these differences may help to clarify the mechanisms responsible for triggering malignant hyperthermia. METHODS To investigate the effects of propofol on Ca2+ regulation by malignant hyperthermia-susceptible skeletal muscle, we determined its effects on the membrane channels and pumps that control myoplasmic Ca2+ concentrations: the sarcoplasmic reticulum ryanodine receptor, the transverse tubule dihydropyridine receptor, and the sarcoplasmic reticulum Ca(2+)-adenosine triphosphatase (Ca(2+)-ATPase). Terminal cisternae-derived sarcoplasmic reticulum vesicles enriched in the junctional proteins of the sarcoplasmic reticulum and the transverse tubule membranes were isolated from the muscle of malignant hyperthermia-susceptible and normal pigs. Ca2+ flux, Ca(2+)-ATPase, and ligand binding measurements on these isolated vesicle preparations were performed in the presence of varying propofol concentrations. RESULTS Propofol (10-500 microM) had no effect on ryanodine receptor-mediated Ca2+ efflux from muscle membrane vesicles. Propofol (1-100 microM) also had no effect on sarcoplasmic reticulum vesicle [3H]ryanodine binding, whereas higher concentrations (200-300 microM) slightly inhibited [3H]ryanodine binding. Binding of the dihydropyridine receptor Ca2+ channel blocker [3H]PN200-110 to these preparations was inhibited by propofol (10-300 microM). Ca(2+)-ATPase activity was stimulated by 10-100 microM propofol but was inhibited by higher concentrations. In all cases, the effects of propofol on malignant hyperthermia-susceptible and normal membrane preparations were similar. CONCLUSIONS In contrast to malignant hyperthermia-triggering inhalation anesthetics, propofol does not stimulate malignant hyperthermia-susceptible or normal ryanodine receptor channel activity, even at > 100 times clinical concentrations. Effects on dihydropyridine receptor and Ca(2+)-ATPase function, however, are similar to the effects of inhalation anesthestics and require much lower concentrations of propofol. These findings, demonstrating that propofol does not activate ryanodine receptor Ca2+ channels, suggest a plausible explanation for why propofol does not trigger malignant hyperthermia in susceptible persons.
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Affiliation(s)
- B R Fruen
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108, USA
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Ledbetter MW, Preiner JK, Louis CF, Mickelson JR. Tissue distribution of ryanodine receptor isoforms and alleles determined by reverse transcription polymerase chain reaction. J Biol Chem 1994; 269:31544-51. [PMID: 7989322] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The tissue distribution of mRNA for ryanodine receptor (ryr) isoforms in various porcine tissues has been determined using the reverse transcription-polymerase chain reaction (RT-PCR). First strand cDNA was synthesized from total tissue RNA with reverse transcriptase and random hexamer primers. PCR primers were selected to amplify an approximately 500-base pair segment from homologous regions near the 5' end of the skeletal (ryr1), cardiac (ryr2), or brain (ryr3) ryr cDNA sequences. The specific amplification of each of the ryr isoforms was confirmed by restriction enzyme mapping and DNA sequencing. A ryr1 RT-PCR product was identified in skeletal muscle and esophagus, a ryr2 RT-PCR product was identified in cardiac muscle, aorta and esophagus, and a ryr3 RT-PCR product was identified in skeletal and cardiac muscle, aorta, esophagus, adrenal gland, small intestine, and lung. All three ryr isoforms were identified throughout the brain, including the parietal, frontal, and temporal lobes of the cerebrum, thalamus/hypothalamus, cerebellum, and brain stem. The normal (Arg615) and mutant (Cys615) ryr1 alleles were expressed in the brains of normal and malignant hyperthermia susceptible pigs, respectively. These results thus demonstrate expression of two ryr isoforms in each type of striated muscle, and all ryr isoforms in a number of regions of the nervous system. The wide distribution of ryr1 in the brain provides a possible neurogenic etiology of malignant hyperthermia.
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Affiliation(s)
- M W Ledbetter
- Department of Biochemistry, University of Minnesota, St. Paul 55108
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Abstract
The altered caffeine sensitivity of malignant hyperthermia-susceptible (MHS) muscle contracture is one basis of the diagnostic test for this syndrome. To determine whether the Arg615-to-Cys615 mutation of the porcine sarcoplasmic reticulum (SR) Ca2+ release channel is directly responsible for this altered caffeine sensitivity, the single-channel kinetics of purified MHS and normal pig Ca2+ release channels were examined. Initial studies demonstrated that decreasing the pH of the medium in either the cis- or trans-chamber decreased the Ca2+ release channel percent open time (Po). The half-inhibitory pH of MHS channels (6.86 +/- 0.04, n = 17) was significantly different from that of normal channels (7.08 +/- 0.07, n = 14). At pH 7.4, in either 7 or 0.12 microM Ca2+, MHS channel Po was not significantly different from that of normal channels over the range 0-10 mM caffeine. Although at pH 6.8 in 7 microM Ca2+ MHS channel Po was greater than that of normal channels over the range 0-20 mM caffeine, the difference could be eliminated by dividing each mean MHS Po by a scaling factor of 3.2. Thus the MHS Ca2+ release channel mutation does not appear to be directly responsible for the altered caffeine sensitivity of MHS pig muscle contracture. Rather, this altered caffeine sensitivity may result from an altered resting myoplasmic Ca2+ concentration or the altered pH and Ca2+ sensitivity of Ca2+ release channel Po of MHS muscle.
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Affiliation(s)
- N H Shomer
- Department of Veterinary Pathobiology, University of Minnesota, St. Paul 55108
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Abstract
The cardiac muscle isoform of the ryanodine receptor/Ca2+ release channel (RYR) has been proposed to be an important target of cyclic ADP-ribose (cADPR) action in mammalian cells. However, we now demonstrate that neither cADPR (0.1-5 microM), nor the related metabolites beta-NAD+ (0.1-30 mM) and ADP-ribose (0.1-5 microM), affected cardiac RYR activity as determined by [3H]ryanodine binding to cardiac sarcoplasmic reticulum (SR) vesicles. Similarly, cADPR (1 microM) failed to activate single cardiac RYR channels in planar lipid bilayers. Skeletal muscle SR [3H]ryanodine binding was also unaffected by cADPR (up to 30 microM). These results argue against a direct role for the well-characterized RYRs of cardiac or skeletal muscle in mediating cADPR-activated Ca2+ release.
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Affiliation(s)
- B R Fruen
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108
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Abstract
The Arg615 to Cys615 mutation of the sarcoplasmic reticulum (SR) Ca2+ release channel of malignant hyperthermia susceptible (MHS) pigs results in a decreased sensitivity of the channel to inhibitory Ca2+ concentrations. To investigate whether this mutation also affects the ion selectivity filter of the channel, the monovalent cation conductances and ion permeability ratios of single Ca2+ release channels incorporated into planar lipid bilayers were compared. Monovalent cation conductances in symmetrical solutions were: Li+, 183 pS +/- 3 (n = 21); Na+, 474 pS +/- 6 (n = 29); K+, 771 pS +/- 7 (n = 29); Rb+, 502 pS +/- 10 (n = 22); and Cs+, 527 pS +/- 5 (n = 16). The single-channel conductances of MHS and normal Ca2+ release channel were not significantly different for any of the monovalent cations tested. Permeability ratios measured under biionic conditions had the permeability sequence Ca2+ >> Li+ > Na+ > K+ > or Rb+ > Cs+, with no significant difference noted between MHS and normal channels. This systematic examination of the conduction properties of the pig skeletal muscle Ca2+ release channel indicated a higher Ca2+ selectivity (PCa2+:Pk+ approximately 15.5) than the sixfold Ca2+ selectivity previously reported for rabbit skeletal (Smith et al., 1988) or sheep cardiac muscle (Tinker et al., 1992) Ca2+ release channels. These results also indicate that although Ca2+ regulation of Ca2+ release channel activity is altered, the Arg615 to Cys615 mutation of the porcine Ca2+ release channel does not affect the conductance or ion selectivity properties of the channel.
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Affiliation(s)
- N H Shomer
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108
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Weaver CD, Shomer NH, Louis CF, Roberts DM. Nodulin 26, a nodule-specific symbiosome membrane protein from soybean, is an ion channel. J Biol Chem 1994; 269:17858-62. [PMID: 7517934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Nodulin 26 is an integral symbiosome membrane protein of nitrogen-fixing soybean nodules. Nodulin 26 is a member of a family of structurally homologous membrane proteins with diverse transport functions. Thus, it has been proposed to be involved in symbiosome membrane transport. Despite this claim, there has not been any evidence that nodulin 26 has a transport activity. In this study, nodulin 26 was purified from soybean nodules by a non-denaturing protocol and was reconstituted into liposomes for channel studies in planar lipid bilayers. Nodulin 26 readily incorporated into bilayers, forming single channels with a maximum unitary conductance of 3.1 nanosiemens (nS) in a recording buffer of 20 mM 3-(N-morpholino)propanesulfonate-NaOH, pH 7.4, 1 M KCl. Nodulin 26 also exhibited multiple, discreet lower conductance states ranging from 0.5 to 2.5 nS. Nodulin 26 channels were voltage-sensitive. The maximal 3.1-nS state was preferentially occupied at lower applied voltages, whereas the lower conductance states were more frequently occupied at higher voltage potentials. Nodulin 26 channels transported both cations and anions, but showed a weak selectivity for anions. These results represent the first purification and functional characterization of the nodulin 26 channel and support a role for this protein in symbiosome membrane transport.
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Affiliation(s)
- C D Weaver
- Department of Biochemistry, University of Tennessee, Knoxville 37996
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Mickelson JR, Ervasti JM, Litterer LA, Campbell KP, Louis CF. Skeletal muscle junctional membrane protein content in pigs with different ryanodine receptor genotypes. Am J Physiol 1994; 267:C282-92. [PMID: 8048487 DOI: 10.1152/ajpcell.1994.267.1.c282] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The content of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase, transverse tubule dihydropyridine receptor (DHPR), and SR ryanodine receptor (RyR) was determined in muscle of pigs homozygous for the normal RyR allele and homozygous or heterozygous for the malignant hyperthermia-susceptible (MHS) RyR allele. Total muscle membranes isolated from 1-day-old pigs of the three different genotypes did not differ in the content of any of these proteins. However, at 28 days of age, crude membranes and total muscle homogenates from homozygous MHS pigs exhibited only 61-81% of the [3H]PN 200-110 or [3H]ryanodine binding of identical preparations isolated from normal pigs; these MHS membranes also contained only 50% of the normal content of each of the DHPR subunits. The crude membranes and muscle homogenates from heterozygous pigs were intermediate to both types of homozygotes in terms of [3H]PN 200-110 binding, [3H]ryanodine binding, and the content of the DHPR subunits. However, membrane preparations enriched in triadic junctional proteins isolated from 3- to 4-mo-old pigs of the three different genotypes did not differ in their [3H]PN 200-110 binding, [3H]ryanodine binding, or Ca(2+)-ATPase activities. We conclude that, although the stoichiometry of the RyR to DHPR is not altered, the presence of the MHS RyR allele during muscle development results in a decreased relative content of these two proteins. This is probably due to a lower junctional membrane content and may be an important ultrastructural consequence of the altered sarcoplasmic Ca2+ regulation in MHS muscle.
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Affiliation(s)
- J R Mickelson
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108
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Fruen BR, Mickelson JR, Roghair TJ, Cheng HL, Louis CF. Anions that potentiate excitation-contraction coupling may mimic effect of phosphate on Ca2+ release channel. Am J Physiol 1994; 266:C1729-35. [PMID: 8023902 DOI: 10.1152/ajpcell.1994.266.6.c1729] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Perchlorate is one of a group of inorganic anions that potentiate excitation-contraction coupling in skeletal muscle. We have compared the effect of perchlorate on the sarcoplasmic reticulum (SR) Ca(2+)-release channel with the effect of inorganic phosphate (Pi), an anion which accumulates in skeletal muscle during exercise. Perchlorate and Pi (10-20 mM) stimulated Ca2+ release from SR vesicles 2- to 3-fold, respectively, and increased ryanodine binding to SR vesicles 1.5-fold. Stimulation of SR Ca(2+)-release channel activity by both perchlorate and Pi was maximal in the presence of micromolar Ca2+ and was associated with an increased affinity of the channel for ryanodine. Other anions known to potentiate muscle contraction (thiocyanate, iodide, and nitrate) also stimulated skeletal muscle SR Ca2+ release and ryanodine binding, as did the Pi analogue vanadate. However, none of the inorganic anions examined altered ryanodine binding to cardiac muscle SR. These results confirm that the SR Ca(2+)-release channel may be a primary site at which perchlorate and other potentiating anions affect skeletal muscle excitation-contraction coupling. In addition, these results demonstrate that the action of these anions on the SR Ca(2+)-release channel resembles that of Pi, a potential endogenous regulator of this channel.
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Affiliation(s)
- B R Fruen
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108
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Affiliation(s)
- C F Louis
- University of Minnesota, Department of Veterinary PathoBiology, St. Paul 55108
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Louis CF, Roghair T, Mickelson JR. Volatile anesthetics inhibit dihydropyridine binding to malignant hyperthermia-susceptible and normal pig skeletal muscle membranes. Anesthesiology 1994; 80:618-24. [PMID: 8141457 DOI: 10.1097/00000542-199403000-00019] [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] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
BACKGROUND Surface membrane dihydropyridine receptor Ca2+ channels may play a role in the response of malignant hyperthermia-susceptible skeletal muscle to volatile anesthetics. METHODS We determined the effect of halothane, enflurane, and isoflurane on the binding of the Ca2+ channel blocker PN200-110 to skeletal muscle membranes isolated from malignant hyperthermia-susceptible and normal pigs. RESULTS In the presence of 0.4 mM halothane, the maximal [3H]PN200-110 binding to both normal and malignant hyperthermia membranes was reduced by 37-43% (P < 0.05). There was no difference in the equilibrium constant for the halothane-dependent inhibition of [3H]PN200-110 binding to these two types of membranes. There also was no significant difference among halothane, enflurane, or isoflurane in their ability to inhibit [3H]PN200-110 binding to either normal or malignant hyperthermia membranes. CONCLUSIONS Volatile anesthetics inhibit the binding of PN200-110 to skeletal muscle membranes by decreasing the number of functionally active dihydropyridine receptor proteins. This inhibition is similar for membranes isolated from both normal and malignant hyperthermia-susceptible muscle, thus providing no evidence for a halothane-induced functional defect in this protein in malignant hyperthermia-susceptible muscle. However, the results of this study also indicate that the mechanism by which volatile anesthetics decrease surface membrane Ca2+ currents in skeletal muscle is by reducing the number of functional dihydropyridine receptor Ca2+ channels.
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Affiliation(s)
- C F Louis
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108
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Fruen BR, Mickelson JR, Shomer NH, Roghair TJ, Louis CF. Regulation of the sarcoplasmic reticulum ryanodine receptor by inorganic phosphate. J Biol Chem 1994; 269:192-8. [PMID: 8276794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
To better understand the mechanisms regulating myoplasmic Ca2+ during muscle activity, we have examined the effect of inorganic phosphate (P(i)) on the ryanodine receptor (RyR) Ca2+ release channel of the sarcoplasmic reticulum (SR). We report that P(i) at concentrations reached in exercising skeletal muscle (3-30 mM) produced a dose-dependent stimulation of ryanodine binding to skeletal muscle SR. Ryanodine binding was increased by 84% in the presence of 30 mM P(i) with half-maximal stimulation at 4 mM P(i). In contrast to its effect on skeletal muscle SR, ryanodine binding to cardiac muscle SR was not stimulated by P(i) (3-30 mM). Stimulation of ryanodine binding to skeletal muscle SR was maximal in the presence of micromolar Ca2+ and was associated with an increased affinity of the RyR for ryanodine (Kd = 204 nM in the absence, versus 107 nM in the presence of 10 mM P(i)). P(i) (10 mM) also increased the rate of Ca2+ release from 45Ca(2+)-filled skeletal muscle SR vesicles by 50% in the presence of micromolar Ca2+. Conversely, arsenate and sulfate (10 mM) had no effect on either ryanodine binding or Ca(2+)-induced Ca2+ release, demonstrating the specificity of the P(i) effect. Single-channel recordings of purified skeletal muscle SR RyR incorporated into planar lipid bilayers showed that addition of 10 mM P(i) to the cis chamber increased the open probability of the channel by 91%. These results demonstrate that concentrations of P(i) which occur in vivo during exercise significantly stimulate the in vitro activity of the skeletal muscle RyR Ca2+ release channel.
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Affiliation(s)
- B R Fruen
- Department of Veterinary PathoBiology, University of Minnesota, St. Paul 55108
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TenBroek EM, Johnson R, Louis CF. Cell-to-cell communication in a differentiating ovine lens culture system. Invest Ophthalmol Vis Sci 1994; 35:215-28. [PMID: 8300349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
PURPOSE This study was performed to determine whether the junctions between both the epithelial and the differentiating fiber-like cells of ovine lens cultures, like gap junctions in other tissues, exhibit cell-to-cell communication that is inhibited by n-octanol, and to determine whether lens connexins and the fiber cell membrane proteins MP20 and MP26 are expressed by these ovine lens cell cultures. METHODS Cells were injected with Lucifer yellow CH to measure cell-to-cell communication. Antibodies to connexin-related lens membrane protein MP70, connexin 43 (Cx43), and connexin 46 (Cx46) and to membrane proteins MP20 and MP26 were used to immunofluorescently label lens cultures and probe Western blots of membranes isolated from lens cultures. RESULTS Both epithelial cells and differentiating clear cells exhibited cell-to-cell transfer of Lucifer yellow that was inhibited by n-octanol. Although a Cx43 antibody immunofluorescently labeled small plaques between the epithelial cells, an MP70 antibody labeled large plaques as well as small punctate areas of the differentiating fiber-like cells. It is interesting that Cx43 and MP70 were frequently present in the same plaques at cell interfaces between epithelial cells as well as some of the larger plaques on the differentiating fiber-like cells. Cx46 and MP70 antibodies labeled the same plaques in membranes of differentiating fiber-like cells and late-stage epithelial cells. The electrophoretic mobility of all three connexin proteins was modified after treatment with alkaline phosphatase. Immunohistochemical staining of these differentiating regions and Western immunoblotting of purified membranes derived from differentiated cultures also showed the presence of MP20 and MP26. CONCLUSIONS The different cell types in the ovine lens culture exhibit gap junction-mediated cell-to-cell communication that is likely effected by one or more of the connexin proteins.
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Affiliation(s)
- E M TenBroek
- Department of Veterinary Biology, University of Minnesota, St. Paul 55108
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Birmachu W, Voss JC, Louis CF, Thomas DD. Protein and lipid rotational dynamics in cardiac and skeletal sarcoplasmic reticulum detected by EPR and phosphorescence anisotropy. Biochemistry 1993; 32:9445-53. [PMID: 8396431 DOI: 10.1021/bi00087a024] [Citation(s) in RCA: 15] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We have used time-resolved phosphorescence anisotropy and electron paramagnetic resonance (EPR) spectroscopy to detect the rotational dynamics of the Ca-ATPase and its associated lipids in dog cardiac sarcoplasmic reticulum (DCSR), in comparison with rabbit skeletal SR (RSSR), in order to obtain insight into the physical bases for different activities and regulation in the two systems. Protein rotational motions were studied with time-resolved phosphorescence anisotropy (TPA) of erythrosin isothiocyanate (ERITC) and saturation-transfer EPR (ST-EPR) of a maleimide spin-label (MSL). Both labels were attached selectively and rigidly to the Ca-ATPase. Lipid rotational motions were studied with conventional EPR of stearic acid spin-labels. As in previous studies on RSSR, the phosphorescence anisotropy decays of both preparations at 4 degrees C were multiexponential, due to the presence of different oligomeric species. The rotational correlation times for the different rotating species were similar for the two preparations, but the total decay amplitude was substantially less for cardiac SR, indicating that more of the Ca-ATPase molecules are in large aggregates in DCSR. ST-EPR spectra confirmed that the Ca-ATPase is less rotationally mobile in DCSR than in RSSR. Lipid probe mobility and fatty acid composition were very similar in the two preparations, indicating that the large differences observed in protein mobility are not due to differences in lipid fluidity. We conclude that the higher restriction in protein mobility observed by both ST-EPR and TPA is due to more extensive protein-protein interactions in DCSR than in RSSR.
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Affiliation(s)
- W Birmachu
- Department of Biochemistry, University of Minnesota Medical School, Minneapolis 55455
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Strasburg GM, Hanson TP, Ouyang HX, Louis CF. Localization and functional role of the calmodulin-binding domain of phospholamban in cardiac sarcoplasmic reticulum vesicles. Biochim Biophys Acta 1993; 1149:249-59. [PMID: 8323944 DOI: 10.1016/0005-2736(93)90208-h] [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] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Limited proteolysis and affinity-labeling techniques have been used to localize the calmodulin-binding domain of phospholamban, the major substrate for both cAMP- and calmodulin-dependent protein kinases in cardiac sarcoplasmic reticulum (SR). SR vesicles, treated with increasing concentrations of trypsin (likely hydrolyzing at Arg-25 in the cytoplasmic region of phospholamban), exhibited a subsequent loss of both cAMP- and calmodulin-dependent phosphorylation, as well as calmodulin affinity-labeling of phospholamban. When SR vesicles were treated with increasing concentrations of chymotrypsin (which likely cleaves at Tyr-6 of phospholamban) there was no effect on the cAMP-dependent phosphorylation of phospholamban. However, similar concentrations of chymotrypsin resulted in a loss of both calmodulin affinity-labeling and calmodulin-dependent phosphorylation of phospholamban (at Thr-17). When SR vesicles were treated with increasing concentrations of Endoproteinase Lys-C (which hydrolyzes phospholamban at Lys-3) both the calmodulin affinity-labeling and the calmodulin-dependent, but not the cAMP-dependent, phosphorylation of phospholamban were inhibited. These data were complemented by 1H-NMR studies on the complex formed by calmodulin and a phospholamban peptide. These data suggest that binding of calmodulin to phospholamban may be an essential intermediate step in the calmodulin-dependent phosphorylation of phospholamban.
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Affiliation(s)
- G M Strasburg
- Department of Food Science and Human Nutrition, Michigan State University, East Lansing
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