Effect of bethanechol, gastrin I, or cholecystokinin on myoelectrical activity.

The purpose of this study was to determine the effect of bethanechol, gastrin I, or the octapeptide of cholecystokinin (CCK-OP) on the smooth muscle of the isolated cat colon. Myoelectrical activity was recorded with monopolar glass-pore electrodes. Slow-wave frequency was 5.9 +/- 0.2 cycles/min during the basal period. Slow waves were generally coupled during the control period and the apparent propagation velocity was predominantly aborad at a velocity of 3.8 +/- 0.4 mm/s. Spike activity was superimposed on 11.9 +/- 1.5% of the slow waves during the control period. Bethanechol stimulated a dose-dependent increase in colonic spike activity, with a threshold concentration of 10(-7) M. Bethanechol did not alter the congruence of the colonic slow-wave frequency at any concentration. Gastrin I or CCK-OP increased colonic spike activity. The threshold concentrations for gastrin I and CCK-OP were 2 X 10(-11) M and 4 x 10(-11) M, respectively. Unlike bethanechol, gastrin I (2 X 10(-9) M - 2 X 10(-8) M) and CCK-OP (4 X 10(-9) - 4 X 10(-8) M) altered slow-wave frequency and decreased slow-wave congruence. These studies suggest that 1) bethanechol, gastrin I, or CCK-OP increases colonic spike activity, and 2) only gastrin I or CCK-OP alters the slow-wave frequency of colonic muscle. Thus neurohumoral substances may act independently on colonic spike activity and colonic slow-wave frequency.