Effects of RHC-80267, an Inhibitor of Diacylglycerol Lipase, on Excitation of Circular Smooth Muscle of the Guinea-Pig Gastric Antrum

Abstract

In small segments of circular smooth muscle isolated from the guinea-pig gastric antrum, the effects of RHC-80267, an inhibitor of diacylglycerol lipase, were investigated both on regenerative slow potentials (either occurring spontaneously or as the result of a depolarizing intracellular current injection) and on the actions of acetylcholine (ACh). As diacylglycerol is a known activator of protein kinase C (PKC), it would therefore be expected that RHC-80267 would activate PKC indirectly. In circular smooth muscle bundles, spontaneously generating slow potentials recorded simultaneously from two given cells were synchronized, indicating that these two cells were electrically coupled. RHC-80267 (0.3-1 µM) increased the frequency of slow potential generation, with no alteration to the amplitude of either the slow potentials or the resting membrane potential. Synchronous electrical activity in a given pair of cells was also unchanged by RHC-80267, indicating that intercellular electrical coupling was not altered. The input resistance of smooth muscle cells calculated from the amplitude of electrotonic potentials produced by injection of current was not significantly altered by RHC-80267. The refractory period for the generation of slow potentials evoked by depolarizing stimuli was about 8 s, and it was decreased to about 5 s by RHC-80267, with no significant alteration to the amplitude of spontaneous or evoked slow potentials. ACh (0.5 µM) depolarized the membrane by about 5 mV and increased the amplitude and frequency of slow potentials. The actions of ACh on the frequency of slow potentials were enhanced by RHC-80267, with no alteration to the amplitudes of both the ACh-induced depolarization and slow potentials. These results support the idea that PKC is involved in determining the frequency of slow potentials, by shortening the refractory period for excitation of gastric smooth muscle cells.

Effects of 5-hydroxytryptamine on electrical responses of circular smooth muscle isolated from the guinea-pig gastric antrum

“…The frequency of slow potentials is also sensitive to the change in membrane potential, and hyperpolarization decreases and depolarization increases the frequency until it reaches to a certain level (about 7 s interval), mainly due to refractory period for the generation of slow potentials (Nose et al, 2000;Kito et al, 2002;Suzuki et al, 2002). The present experiments indicated that the frequency of slow potentials was increased or decreased by 5-HT, with associated hyperpolarization of the membrane.…”

Factors which determine the duration of follower potentials in longitudinal smooth muscle isolated from the guinea-pig stomach antrum

“…Proteinkinase C (PKC) is one of the factors involved in the regulation of the frequency of spontaneous activity in gastric muscles, and inhibition of the activity of PKC decreases and activation increases the frequency Suzuki et al, 2002b;Lee et al, 2004;Nakamura and Suzuki, 2004a;Nakamura and Suzuki, 2004b;Suzuki et al, 2006). The present experiments showed that chelerythrine decreased the frequency of follower potentials, with no change in the amplitude and duration, and the I-D relationship shifted to the right-hand and upward direction, with no change in the slope (Fig.…”

Metabolic component of the temperature-sensitivity of slow waves recorded from gastric muscle of the guinea-pig

“…It is proposed in murine small intestine that Ca 2+ extrusion from mitochondria activates ion channels at the plasma membrane to form pacemaker potentials (Ward et al, 2000), while in the guinea-pig stomach, IP3 formation is stimulated by elevation of cytosolic Ca 2+ due to mitochondria-derived Ca 2+ release, possibly through activation of protein kinase C (Kito et al, 2002b;Suzuki et al, 2002). In both hypotheses, mitochondrial Ca 2+ handling may have a pivotal role in the production of rhythmic activity (Kito and Suzuki, 2003b).…”