Mechanical and electrical activity in intestinal smooth muscle

¹ Department of Physiology, University of Illinois, Urbana, Illinois

Rings of ganglion-free circular muscle from cat intestine show, in addition to circling conduction, waves which are transmitted along the long axis of the intestine at about 0.7 cm/sec. and in bands about 1.2 mm in width. Evidence against the mechanical pull hypothesis for transmission include the facts that strips of the circular muscle do not respond to brief stretches, conduction may occur through a clamped region which does not pass a mechanical wave, electrical responses may persist under tensions at which shortening does not occur, and drugs may cause some dissociation of electrical and mechanical responses. It is concluded that conduction is independent of mechanical pull. Intracellular electrodes recorded resting potentials with a mean value of 40 mv, conducted action potentials with a mean of 22 mv. Conducted responses fail to follow at intervals less than about 1 second, whereas single fibers may give multiple responses 0.3 seconds apart and double spikes only 40 msec. apart.