Transmission in Ganglion-Free Circular Muscle From the Cat Intestine

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

Rings and strips of circular muscle from cat intestine show bursts of fast potentials (each 0.05–0.1 sec. duration) in spontaneous or barium-induced activity or in response to shocks. Conduction in the long direction of the fibers is at 4 cm/sec.; there is some lateral conduction at about 3 cm/sec. which decrements, leaving an active band about 3 mm wide to spiral around a ring of muscle. If a ring is partly slit, forming two rings connected by a bridge, a wave of activity may cross from one side to the other; crossing depends on local excitability which may be enhanced by citrate or barium or may be depressed by high potassium, and conduction may go in one or both directions. If the slit is complete, similar crossing occurs if the two rings are in close contact for as little as one-fifth of their circumference. Crossing at a zone of contact is not stopped by saline shunt and resembles normal spiral conduction. Short-fibered muscle has higher resistance and shows a greater reactive component than long-fibered muscle although in intestinal muscle the cell membranes must impose relatively little resistance. Electron microscopy reveals no sarcoplasmic continuity from fiber to fiber. An ephaptic hypothesis of interfiber conduction is suggested.