Excitation-contraction coupling in crayfish

Abstract

High-sensitivity recording techniques demonstrate a continuous relation between the onset and magnitude ot tension and the membrane depolarization that is induced by increasing K in the bathing medium or by intracellularly applied outward currents. This finding is not consistent with the mechanism of signalling e-c coupling by electrotonic spread of a "critical" depolarization inward along the membrane of the transverse tubular system. It is in accord, however, with the channelled current mechanism that is based on the known anion-permselectivity of the membrane in the terminals of the TTS. The channelled-current model also predicts a direct role of Cl and a possible interaction between Ca and CI in e-c coupling. The initiation and maintenance of tension as well as its magnitude, are in fact dependent upon the concentrations of Ca and Cl in the medium. Thus, both the signalling to, and the activation of, the contractile system appear to be performed by a flow of current in the loop: cell membrane - cell interior - TTS membrane - TTS channels - exterior, as is envisaged in the channelled-current model of e-c coupling. © 1967 by the American Society of Zoologists.