Voltage dependency of the frequency of slow waves in antrum smooth muscle of the guinea-pig stomach

The effects of membrane depolarization on the frequency of spontaneous acti vities were investigated in circular smooth muscle of the guinea-pig antrum attached with (intact tissue) or without longitudinal muscles (circular ti ssue). 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+ conc entrations depolarized the membrane and reduced the amplitude and interval between spontaneous activities in both tissues; the amplitude was reduced l inearly with depolarization and disappeared at about -35 mV; the interval w as reduced successively with depolarization and reached a stable value (abo ut 8 s) at about -45 mV. The depolarization and reduction in amplitude and interval of spontaneous activities induced by high K+ solution were not alt ered by atropine, nitroarginine, or apamin in either tissue, suggesting tha t these changes did not involve the effects of neurotransmitters. The depol arization of the membrane by electrical stimulation also reduced the amplit ude 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 wa s 8-12s. The results indicate that the frequency of slow waves increases wi th a depolarization of the membrane up to -45mV, irrespective of the presen ce of caffeine-insensitive components. A depolarization of the membrane abo ve -45 mV does not further increase the frequency of slow waves, possibly b ecause of the refractory period for the generation of slow waves.