ARTICLES

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.