妊娠子宮平滑筋の膜興奮性の変化に関するラット単離細胞を用いた電気生理学的検討
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概要
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The present study was undertaken to clarify whether gestational changes in ion channels of pregnant myometrial cells cause changes in characteristics of membrane potential during gestation and whether the tocolytic β-stimulant affects the membrane currents in these cells. The patch clamp method was applied to single smooth muscle cells freshly isolated from the longitudinal layer of pregnant rat uterus at middle stage (14th day) and late stage (20th day) of gestation. Resting membrane potential and action potential were investigated using the current clamp mode. Resting membrane potential of the cells on the 14th day (D14 cells) and the 20th day (D20 cells) of pregnancy was -56.9±3.9 mV and -46.6±2.6 mV, respectively. The maximum rate of rise of action potential (dV/dtmax) of the D20 cells was larger than that of the D14 cells. Membrane currents were investigated using the voltage clamp mode. The density of the outward K+ current (IK) of the D20 cells was less than that of the D14 cells. In analysis of the steady-state activation curve for IK, half activation voltage for the currents of the D14 cells was 10.6±1.2 mV and that of the D20 cells was 12.7±1.0 mV. The above difference between the gestational stages was not statistically significant. The results showed that voltage dependency for the activation of IK was not altered through the gestational stages. Maximum conductance for IK of the D20 cells was decreased as compared with that of the D14 cells (178.6±11.5pS/pF for the D20 cells, 382.9±43.2pS/pF for the D14 cells). These findings indicate that the density of K+ channel decreases at late gestational stage. In order to examine the effect of β-adrenergic stimulation on the membrane current, isoproterenol (0.1 to 100 μ/M) was applied to the single myometrial cells. In both gestational stages, isoproterenol produced no significant change in the K+ and Ca2+ currents. All these results show that the decrease in density of K+ channel mainly contributes to the depolarization of resting membrane potential of myometrial cells at late gestational stage. Furthermore, it is suggested that the decrease in K+ channel density causes the increase in dV/dtmax of action potential.
- 札幌医科大学の論文
- 1996-12-01
札幌医科大学 | 論文
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