Fast Na+ channels and slow Ca2+ current in smooth muscle from pregnant rat uterus.
Fast Na+ channels and slow Ca2+ current in smooth muscle from pregnant rat uterus.
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DOI：
10.1007/bf00240301
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发表时间：
1992-09
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影响因子：
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通讯作者：
Nick Sperelakis;Y. Inoue;Yusuke Ohya
中科院分区：
文献类型：
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作者：
Nick Sperelakis;Y. Inoue;Yusuke Ohya
Smooth muscle cells normally do not possess fast Na2+channels, but inward current is carried through two types of Ca2+channels: slow (L-type) Ca2+channels and fast (T-type) Ca2+channels. Using whole-cell voltage clamp of single smooth muscle cells isolated from the longitudinal layer of 18-day pregnant rat uterus, depolarizing pusles, applied from a holding potential of −90 mV, evoked two types of inward current, fast and slow [8]. The fast inward current decayed within 30 ms, depended on [Na]0, and was inhibited by TTX (K0.5= 27 nM). The slow inward current decayed slowly, was dependent on [Ca]0, and was inhibited by nifedipine. These results suggest that the fast inward current is a fast Na2+channel current, and that the slow inward current is a Ca2+channel current was not evident. Thus, the ion channels which generate inward currents in pregnant rat uterine cells are TTX-sensitive fast Na+channels and dihudropuridine-sensitive slow Ca2+channels. The number of fast Na+channels increased during gestation [9]. The averaged current density increased from 0 on day 5, to 0.19 on day 9, to 0.56 on day 14, to 0.90 on day 18, and to 0.86 pA/pF on day 21. This almost linear increase occurs because of an increase in the fraction of cells which possess fast Na2+channels, and it suggested that the fast Na+current may be involved in spread of excitation. The Ca2+channel current density also was higher during the latter half of gestation. These results indicate that the fast Na+channels and Ca2+slow channels in myometrium become more numerous as term approaches, and may facilitate parturition. Isoproterenol (beta-agonist) did not affect either ICa(s)or INa(f), whereas Mg2+(K0.5of 12 mM) and nifedipine (K0.5of 3.3 nM) depressed ICa(s). Oxytocin had no effect on INa(f)and actually depressed ICa(s)to a small extect. Therefore, the tocolytic action of beta-agonists cannot be explained by an inhibition of ICa(s), whereas that of Mg2+can be so explained. The stimulating action of oxytocin on uterine contractions is not due to stimulation of ICa(s).
