Voltage Dependency of the Frequency of Slow Waves in Antrum Smooth Muscle of the Guinea-Pig Stomach.

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Abstract
The effects of membrane depolarization on the frequency of spontaneous activities were investigated in circular smooth muscle of the guinea-pig antrum attached with (intact tissue) or without longitudinal muscles (circular tissue). Both types of tissue were spontaneously active; the intact tissues generated slow wave and circular tissues generated regenerative potential. The latter but not the former was abolished by caffeine. Increasing K(+) concentrations depolarized the membrane and reduced the amplitude and interval between spontaneous activities in both tissues; the amplitude was reduced linearly with depolarization and disappeared at about -35 mV; the interval was reduced successively with depolarization and reached a stable value (about 8 s) at about -45 mV. The depolarization and reduction in amplitude and interval of spontaneous activities induced by high K(+) solution were not altered by atropine, nitroarginine, or apamin in either tissue, suggesting that these changes did not involve the effects of neurotransmitters. The depolarization of the membrane by electrical stimulation also reduced the amplitude and interval of spontaneous activities in both tissues, in a potential-dependent way. The absolute refractory period for generation of the evoked regenerative potential was about 8 s, and the relative refractory period was 8--12 s. The results indicate that the frequency of slow waves increases with a depolarization of the membrane up to -45 mV, irrespective of the presence of caffeine-insensitive components. A depolarization of the membrane above -45 mV does not further increase the frequency of slow waves, possibly because of the refractory period for the generation of slow waves.