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Voltage‐controlled Ca 2+ release in normal and ryanodine receptor type 3 (RyR3)‐deficient mouse myotubes
Author(s) -
Dietze B.,
Bertocchini F.,
Barone V.,
Struk A.,
Sorrentino V.,
Melzer W.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.003by.x
Subject(s) - ryanodine receptor , biophysics , depolarization , myogenesis , intracellular , endoplasmic reticulum , repolarization , chemistry , membrane potential , voltage clamp , patch clamp , myocyte , biology , medicine , endocrinology , electrophysiology , receptor , biochemistry
1 Primary cultured myotubes were derived from satellite cells of the diaphragm obtained from both normal mice (RyR3+/+) and mice with a targeted mutation eliminating expression of the type 3 isoform of the ryanodine receptor (RyR3−/−). Using the whole‐cell patch clamp technique, L‐type Ca 2+ currents were measured during step depolarizations. Simultaneously, intracellular Ca 2+ transients were recorded with the fluorescent indicator dye fura‐2. 2 After correction for non‐instantaneous binding of Ca 2+ to the indicator dye and taking into account the dynamics of Ca 2+ binding to intracellular constituents, an estimate of the time course of the Ca 2+ release rate from the sarcoplasmic reticulum (SR) was obtained. 3 The calculated SR Ca 2+ release flux exhibited a marked peak within less than 12 ms after the onset of the voltage‐clamp depolarization and fell rapidly thereafter to a five times lower, almost steady level. It declined rapidly after termination of the depolarization. 4 Signals in normal and RyR3‐deficient myotubes showed no significant difference in the activation of Ca 2+ conductance and in amplitude, time course and voltage dependence of the Ca 2+ efflux from the SR. 5 In conclusion, the characteristics of voltage‐controlled Ca 2+ release reported here are similar to those of mature mammalian muscle fibres. In contrast to differences observed in the contractile properties of RyR3‐deficient muscle fibres, a contribution of RyR3 to excitation‐contraction coupling could not be detected in myotubes.