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Intramembrane charge movement and sarcoplasmic calcium release in enzymatically isolated mammalian skeletal muscle fibres
Author(s) -
Szentesi Peter,
Jacquemond Vincent,
Kovács László,
Csernoch László
Publication year - 1997
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.1469-7793.1997.371bb.x
Subject(s) - calcium , chemistry , depolarization , biophysics , guinea pig , skeletal muscle , endoplasmic reticulum , contraction (grammar) , voltage clamp , membrane potential , anatomy , endocrinology , biochemistry , biology , organic chemistry
1 Single muscle fibres were dissociated enzymatically from the extensor digitorum longus and communis muscles of rats and guinea‐pigs. The fibres were mounted into a double Vaseline gap experimental chamber and the events in excitation–contraction coupling were studied under voltage clamp conditions. 2 The voltage dependence of intramembrane charge movement followed a two‐state Boltzmann distribution with maximal available charge of 26.1 ± 1.5 and 26.1 ± 1.3 nC μF −1 , mid‐point voltage of –35.1 ± 5.0 and –42.2 ± 1.2 mV and steepness of 16.7 ± 2.2 and 17.0 ± 1.9 mV (means ± s.e.m. , n = 7 and 4) in rats and guinea‐pigs, respectively. 3 Intracellular calcium concentration ([Ca 2+ ] i ) was monitored using the calcium‐sensitive dyes antipyrylazo III, fura‐2 and mag‐fura‐5. Resting [Ca 2+ ] i was similar in rats and guinea‐pigs with 125 ± 18 and 115 ± 8 n m ( n = 10 and 9), respectively, while the maximal increase for a 100 ms depolarization to 0 mV was larger in rats (6.3 ± 1.0 μ m ; n = 7 ), than in guinea‐pigs (2.8 ± 0.3; n = 4 ). 4 The rate of calcium release (R rel ) from the sarcoplasmic reticulum (SR) displayed an early peak followed by a fast and a slow decline to a quasi maintained steady level. After normalizing R rel to the estimated SR calcium content (1.2 ± 0.1 and 0.9 ± 0.1 m m in rats and guinea‐pigs, respectively) and correcting for depletion of calcium in the SR the peak and steady levels at 0 mV, respectively, were found to be 2.50 ± 0.08 and 0.81 ± 0.06% ms −1 in rats and 2.43 ± 0.25 and 0.88 ± 0.01 % ms −1 in guinea‐pigs. The voltage dependence was essentially the same in both species, but different from that in amphibians. 5 These experiments show that enzymatic isolation yields functionally intact mammalian skeletal muscle fibres for Vaseline gap experiments. The data also suggest a close connection in the regulation of the different kinetic components of SR calcium release in mammalian skeletal muscle.