Composition of vacuoles and sarcoplasmic reticulum in fatigued muscle: electron probe analysis.

Abstract

Electron probe analysis, cryo-ultramicrotomy and freeze-substitution were used to determine the nature of vacuolation and subcellular composition in fatigued frog skeletal muscle fibers. The vacuoles caused by fatigue were part of the T[transverse]-tubule system and contained high concentrations of NaCl. The Ca concentration in the terminal cisternae was higher than previously measured normal resting values. Mitochondrial Ca content was relatively low (mean .+-. SEM [standard error of mean]; 2 .+-. 2 mmol/kg dry wt). Fiber NaCl was increased. Fatigue was not due to depletion of Ca stores from the terminal cisternae or to uncoupling of mitochondria due to Ca loading, but may be caused by multiple mechanisms including failure of the T-tubule action potential.