Effect of perchlorate on calcium release in skinned fibres stimulated by ionic substitution and caffeine

We have determined the effects of the perchlorate ion on the contracture of skinned (sarcolemma removed) skeletal muscle fibres, stimulated either by ionic substitution or caffeine. Calcium release was monitored in single cells by measuring the peak height of tension transients. Perchlorate significantly sensitizes fibres to activation by ionic substitution, a manipulation that is thought to trigger calcium release via the normal physiological pathway. Adding 0.8 mM perchlorate to the solutions shifted the curve relating the magnitude of ionic substitution to the level of activation leftward, such that smaller stimuli were needed to produce a contracture of a given height. Perchlorate could also trigger a contracture directly. Exposing fibres to 1.0 mM perchlorate caused contractures averaging 60% of bracketing controls. In contrast to contractures stimulated by ionic substitution, those triggered by caffeine were unaffected by perchlorate. Since caffeine is thought to act directly on the sarcoplasmic reticulum to cause calcium release, these results suggest that perchlorate enhances activation in skinned fibres by interacting with transverse tubular membranes.