title: Alterations of excitation-contraction coupling and excitation coupled Ca(2+)  entry in human myotubes carrying CAV3 mutations linked to rippling muscle.
abstract: Rippling muscle disease is caused by mutations in the gene encoding caveolin-3 (CAV3), the muscle-specific isoform of the scaffolding protein caveolin, a protein involved in the formation of caveolae. In healthy muscle, caveolin-3 is responsible for the formation of caveolae, which are highly organized sarcolemmal clusters influencing early muscle differentiation, signalling and Ca(2+) homeostasis. In the present study we examined Ca(2+) homeostasis and excitation-contraction (E-C) coupling in cultured myotubes derived from two patients with Rippling muscle disease with severe reduction in caveolin-3 expression; one patient harboured the heterozygous c.84C>A mutation while the other patient harbored a homozygous splice-site mutation (c.102+ 2T>C) affecting the splice donor site of intron 1 of the CAV3 gene. Our results show that cells from control and rippling muscle disease patients had similar resting [Ca(2+) ](i) and 4-chloro-m-cresol-induced Ca(2+) release but reduced KCl-induced Ca(2+) influx. Detailed analysis of the voltage-dependence of Ca(2+) transients revealed a significant shift of Ca(2+) release activation to higher depolarization levels in CAV3 mutated cells. High resolution immunofluorescence analysis by Total Internal Fluorescence microscopy supports the hypothesis that loss of caveolin-3 leads to microscopic disarrays in the colocalization of the voltage-sensing dihydropyridine receptor and the ryanodine receptor, thereby reducing the efficiency of excitation-contraction coupling.
authors.affiliation: Department of Physiology, University of Bern, Switzerland.
authors.forename: Nina D
authors.initials: ND
authors.lastname: Ullrich
authors.forename: Dirk
authors.initials: D
authors.lastname: Fischer
authors.forename: Cornelia
authors.initials: C
authors.lastname: Kornblum
authors.forename: Maggie C
authors.initials: MC
authors.lastname: Walter
authors.forename: Ernst
authors.initials: E
authors.lastname: Niggli
authors.forename: Francesco
authors.initials: F
authors.lastname: Zorzato
authors.forename: Susan
authors.initials: S
authors.lastname: Treves
mesh_terms: D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism; D051244:Caveolin 3 / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D003408:Cresols / Q000494:pharmacology; D056966:Excitation Contraction Coupling; D006801:Humans; D009119:Muscle Contraction / Q000235:genetics / Q000502:physiology; D024510:Muscle Development / Q000235:genetics; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism; D009135:Muscular Diseases / Q000235:genetics* / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism
chemical_list: C417736:CAV3 protein, human; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D051244:Caveolin 3; D003408:Cresols; D019837:Ryanodine Receptor Calcium Release Channel; C006984:chlorocresol; D011189:Potassium Chloride; D002118:Calcium