Some dielectric properties of muscle membrane and their possible importance for excitation-contraction coupling.

Voltage-clamp studies of polarization currents have shown the presence of polar molecules in the membrane of skeletal muscle. Their high dipole moment and favorable transition potential suggest that they may be "gating molecules" which serve to regulate some membrane potential-dependent physiological function. Experiments with the drugs tetrodotoxin and tetracaine show that these polar molecules are unlikely to play a role in regulating the sodium and potassium channels responsible for electrical excitation. Instead, they may regulate calcium release from the sarcoplasmic reticulum, which also depends steeply on the cell membrane potential. Schneider and Chandler's hypothesis whereby calcium release from the sarcoplasmic reticulum is regulated by voltage-sensitive "gating molecules" in the tubule membrane is still unproven, but remains attractive and plausible.