Resting tension, “negative” contraction and “break” contraction in specialised crustacean muscle fibers

Abstract

AbstractA few tinted fibers (color grey‐brown‐pink) occur in certain crustacean muscles of diverse species. Many of these were found to have relatively low resting membrane potentials and to be developing tension continually in the normal resting state, i.e., in the absence of extrinsic stimulation. This tension is rapidly relaxed if polarizing current is passed across the membrane. The relaxation in response to a brief polarizing pulse follows a time‐course resembling that of a twitch, but is, of course, the inverse. Fibers which were similar in color but which did not show resting tension often gave a strong contraction when a polarizing current was turned off. These “break contractions” had a slower time‐course than normal twitches. The relaxation rate was accelerated by polarizing pulses. Possible explanations of the phenomena are offered in terms of modern views on excitation‐contraction coupling.