Regulation of L-type Calcium Channel Current by Somatostatin in Guinea-Pig Gastric Myocytes

To study the direct effect of somatostatin (SS) on calcium channel current () in guinea-pig gastric myocytes, was recorded by using whole-cell patch clamp technique in single smooth muscle cells. Nicardipine (), a L-type channel blocker, inhibited by % (n=5), however was decreased in a reversible manner by application of SS. The peak at 0 mV were decreased to , , , , % at , , , , M of SS, respectively (n=3∼6; ). The steady-state activation and inactivation curves of as a function of membrane potentials were well fitted by a Boltzmann equation. Voltage of half-activation () was mV in control and mV in SS treated groups (respectively, n=5). The same values of half-inactivation were mV and mV (respectively, n=5). There was no significant difference in activation and inactivation kinetics of by SS. Inhibitory effect of SS on was significantly reduced by either dialysis of intracellular solution with , a non-hydrolysable G protein inhibitor, or pretreatment with pertussis toxin (PTX). SS also decreased contraction of guinea-pig gastric antral smooth muscle. In conclusion, SS decreases voltage-dependent L-type calcium channel current () via PTXsensitive signaling pathways in guinea-pig antral circular myocytes.