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 the subcellular composition in fatigued frog skeletal muscle fibers. The vacuoles caused by fatique were part of the T-tubule system and contained high concentrations of NaCl. The calcium concentrations in the terminal cisternae was higher than previously measured normal resting values. Mitochondrial calcium content was relatively low (mean ± SEM,2 ± 2 mmol/kg dry weight). Fiber naCl was increased. It is concluded that fatique is not due to the depletion of calcium stores from the terminal cisternae or to uncoupling of mitochondria due to calcium loading but may be caused by multiple mechanisms including failure of the T-tubule action potential.