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