Effects of fatigue on depolarization- and caffeine-induced contractures of skinned fibres.

Aims: Fatigue has been shown to cause intrinsic alterations in sarcoplasmic reticulum (SR) Ca2+ release.
Methods: In this investigation, frog semitendinosus muscles were stimulated to fatigue, in vitro (80 Hz, 100 ms, 1 train s-1, 5 min). Immediately after stimulation, single fibres were removed and skinned using either chemically or mechanically skinning. Contralateral muscle were treated similarly but were not stimulated.
Results: In fatigued, saponin skinned fibres, contracture responses to low [caffeine] (4-8 mm) were depressed compared with control. However, responses to high concentrations (10-15 mm) were not different between conditions. In the fatigued, mechanically skinned fibres, responses to chloride depolarization were depressed at all [chloride] (20-100 mm) compared with control.
Conclusions: These results suggest that fatigue causes intrinsic alterations in both the SR Ca2+ release channel as well as communication between the transverse-tubule and the SR.