Modulation of the Pacemaker Activity in Circular Muscle of the Canine Colon

The smooth muscle cells of the circular muscle layer of the canine colon exhibit periodic waves of depolarization (slow waves) which serve a pacemaker function similar to that of their counterparts in the small intestine (1). Slow waves bring the membrane potential periodically close to or above threshold for spiking activity. Slow waves with spiking activity on their peak depolarizations are associated with phasic contractions (1,2). In …