EFFECTS OF PERCHLORATE ON EXCITATION CONTRACTION COUPLING IN FROG AND CRAYFISH SKELETAL-MUSCLE

1. The effects of perchlorate on various aspects of excitation-contraction coupling in frog and crayfish skeletal muscle have been examined in optical and electrophysiological experiments on voltage-clamped cut muscle fibres. 2. In the frog, perchlorate shifted the voltage dependence of charge movement and consequent sarcoplasmic reticulum (SR) Ca2+ release, but it had little effect on the slow inward calcium current. 3. In the crayfish, perchlorate had little effect on either calcium currents or the SR Ca2+ release that contributes to myoplasmic Ca2+ elevations. 4. Two alternative explanations for these results are discussed. There may be two functional types of dihydropyridine receptors, those (perchlorate sensitive) that communicate with the ryanodine receptor via charge movement and those (perchlorate insensitive) that function solely as Ca2+ entry points. Alternatively, the results would be consistent with two separate voltage sensors on each dihydropyridine receptor, only one of which is perchlorate sensitive.