The study of cell membrane ion channels involving in automaticity of human uterine smooth muscle cells.

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The aim of this study was to find the membrane channels which involves in automaticity of human myometrium. For the beginning, we tried to record hyperpolarization-induced inward current which was recorded in rat myometrium using patch clamp methods, but it failed. So we evaluated the difference in the expression of mRNA of two types of calcium channels between longitudinal and circular muscle layer of rat mayometrium during pregnancy. Changes in the expressions of the mRNA encoding L-type (α1C) and T-type (α1G, α1H, and all) calcium channels in longitudinal and circular smooth muscle cells of the rat myometrium were examined using a comparative kinetic RT/PCR method. During the course of pregnancy, α1C mRNA expression showed an N-shaped change in longitudinal muscle, but simply increased after mid pregnancy in circular muscles. The mRNAs for α1G and α1H, but not that for all, were expressed in both longitudinal and circular smooth muscle. In longitudinal muscle, the changes in α1H mRNA was similar to that in α1C mRNA during gestation, but the expression of α1G mRNA changed significantly only at term (day 22). In circular muscle, α1H mRNA expression was stable at any stage during pregnancy, but α1G mRNA significantly increased on day 15 and at term. No relationship was observed between voltage-dependent calcium-channel mRNA expressions and either proliferation or hypertrophy of circular muscle during pregnancy. These results show, (a)that during pregnancy, the expression levels of L-type channels change dynamically, and it may contribute directly to the regulation of cell excitability, and (b)that the T-subtype that increases during pregnancy differs between longitudinal and circular muscle cells, although their functions remain unclear.