Myogenic regulation of propagation in gastric smooth muscle

Experiments were performed to test the effects of frequency and stretch on the velocity of slow wave propagation parallel and perpendicular to the long axis of circular muscle fibers in the canine gastric antrum. Slow waves were evoked from one corner of a rectangular sheet of muscle and propagated throughout the tissue. Mathematics were derived and are presented, which simultaneously compute conduction velocities in each direction, regardless of electrode positions. Increased rate of stimulation had no significant effect on conduction velocity in the circumferential axis, but propagation slowed in the axis perpendicular to the circular fibers by an average of 25% over interstimulus intervals between 12 and 60 s. Conduction velocity was also a function of the degree of stretch. The most rapid conduction velocity occurred when muscles were stretched to an average of 118% of the resting, fasted length found in situ in the axis parallel to the circular fibers and 140% in the axis perpendicular to the circular fibers. Propagation was blocked by stretching muscles past 200% of resting length. These results suggest that the frequency of slow waves and gastric distension are intrinsic mechanisms capable of regulating the spread of slow waves.