scholarly journals The effects of reducing the extracellular calcium concentration on the twitch in isolated frog's skeletal muscle fibres.

1982 ◽  
Vol 32 (4) ◽  
pp. 589-608 ◽  
Author(s):  
George B. FRANK
Keyword(s):  
Skeletal Muscle ◽  
Calcium Concentration ◽  
Extracellular Calcium ◽  
Muscle Fibres ◽  
Extracellular Calcium Concentration ◽  
Skeletal Muscle Fibres

Stimulation frequency and external ionic composition control the repriming of caffeine-induced contractures in frog skeletal muscle

1987 ◽  
Vol 65 (4) ◽  
pp. 704-710 ◽  
Author(s):  
Guy Raymond ◽  
Daniel Potreau ◽  
Christian Cognard ◽  
Jean-Claude Jacquenod ◽  
Jean-Pierre Poindessault
Keyword(s):  
Skeletal Muscle ◽  
Calcium Concentration ◽  
Ionic Composition ◽  
Fold Increase ◽  
Muscle Fibres ◽  
Composition Control ◽  
Slow Inward Calcium Current ◽  
Skeletal Muscle Fibres ◽  
External Calcium ◽  
Caffeine Contractures

The effect of stimulation rate and of external ionic composition on the repriming period of contractures induced by 6 mM caffeine was tested on isolated skeletal muscle fibres of the frog (Rana ridibunda). The repriming period, which was 11.2 ± 0.1 min (mean ± SEM, n = 9) on quiescent fibres, was shortened in fibres stimulated at a frequency ranging from 3 to 12 min−1 (optimal rate, 8 min−1; full repriming 5.7 ± 0.2 min; n = 10). A 10-fold increase in the extracellular calcium concentration shortened the repriming period on both stimulated and quiescent fibres, whereas decreasing external calcium (1/10) delayed it. In a Na+-free solution (Li+ substituted) the repriming period of stimulated fibres was markedly delayed (14 min), whereas quiescent fibres never recover more than 10% of their ability to develop subsequent caffeine contractures. In contrast, with a 35% Na solution, the repriming period was greatly shortened (stimulated, 5.4 ± 0.2 min, n = 7; quiescent, 6.2 ± 0.5 min, n = 8). It is concluded that repriming depends on three mechanisms that seem to refill a calcium store and trigger recovery: the slow inward calcium current, a Na+–Ca2+ exchange, and perhaps a passive Ca2 influx.

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