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

  • Kim, Young-Chul (Department of Physiology, Chungbuk National University College of Medicine) ;
  • Sim, Jae-Hoon (Department of Physiology and Biophysics, Seoul National University College of Medicine) ;
  • Lee, Sang-Jin (Department of Physiology, Chungbuk National University College of Medicine) ;
  • Kang, Tong-Mook (Department of Physiology, Sungkyunkwan University School of Medicine) ;
  • Kim, Sung-Joon (Department of Physiology and Biophysics, Seoul National University College of Medicine) ;
  • Kim, Seung-Ryul (Department of Biochemistry, Chungbuk National University College of Medicine) ;
  • Youn, Sei-Jin (Department of Internal Medicine, Chungbuk National University College of Medicine) ;
  • Lee, Sang-Jeon (Department of Surgery, Chungbuk National University College of Medicine) ;
  • Xu, Wen Xie (Department of Physiology, Medical School, Shaghai Jiao Tong University) ;
  • So, In-Suk (Department of Physiology and Biophysics, Seoul National University College of Medicine) ;
  • Kim, Ki-Whan (Department of Physiology and Biophysics, Seoul National University College of Medicine)
  • Published : 2005.04.21

Abstract

To study the direct effect of somatostatin (SS) on calcium channel current ($I_{Ba}$) in guinea-pig gastric myocytes, $I_{Ba}$ was recorded by using whole-cell patch clamp technique in single smooth muscle cells. Nicardipine ($1{\mu}M$), a L-type $Ca^{2+}$ channel blocker, inhibited $I_{Ba}$ by $98{\pm}1.9$% (n=5), however $I_{Ba}$ was decreased in a reversible manner by application of SS. The peak $I_{Ba}$ at 0 mV were decreased to $95{\pm}1.5$, $92{\pm}1.9$, $82{\pm}4.0$, $66{\pm}5.8$, $10{\pm}2.9$% at $10^{-10}$, $10^{-9}$, $10^{-8}$, $10^{-7}$, $10^{-5}$ M of SS, respectively (n=3∼6; $mean{\pm}SEM$). The steady-state activation and inactivation curves of $I_{Ba}$ as a function of membrane potentials were well fitted by a Boltzmann equation. Voltage of half-activation ($V_{0.5}$) was $-12{\pm}0.5$ mV in control and $-11{\pm}1.9$ mV in SS treated groups (respectively, n=5). The same values of half-inactivation were $-35{\pm}1.4$ mV and $-35{\pm}1.9$ mV (respectively, n=5). There was no significant difference in activation and inactivation kinetics of $I_{Ba}$ by SS. Inhibitory effect of SS on $I_{Ba}$ was significantly reduced by either dialysis of intracellular solution with $GDP_{\beta}S$, 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 ($VDCC_L$) via PTXsensitive signaling pathways in guinea-pig antral circular myocytes.

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