Abstract
In isolated circular muscle bundle of the guinea-pig stomach antrum, smooth muscle cells had the resting membrane potential of about -70 mV, and they produced periodical generation of slow potentials (amplitude 25 - 40 mV, duration 5 - 7 s, frequency 0.2 - 5/min). Acetylcholine (ACh), 1 - 100 nM, increased the amplitude and frequency of slow potentials with no significant depolarization of the membrane, and the actions of ACh were abolished by atropine. Chelerythrine, 0.1 - 1 μM, reduced the frequency of slow potentials, with no alteration to the amplitude of slow potentials and the resting membrane potential. The ACh-induced increase in frequency, but not the amplitude, of slow potentials was inhibited by chelerythrine. 2-APB, 3 μM, increased the frequency of slow potentials and decreased the amplitude, with depolarization of the membrane. In the presence of 2-APB, ACh increased the frequency of slow potentials, with no significant increase in the amplitude. A known activator of proteinkinase C, phorbol 12, 13-dibutyrate (PDBu), 1 nM, increased the frequency, but not the amplitude, of slow potentials, with no depolarization of the membrane, and the effects were antagonized by chelerythrine. Thus, the ACh-induced increase in the frequency of slow potentials was mimicked by PDBu. The results suggest that ACh increases the frequency of slow potentials by activating proteinkinase C. The amplitude of slow potentials may be related to the amount of Ca released from internal stores through activation of IP3 receptors. [Jpn J Physiol 54 Suppl:S124 (2004)]
