Shimamura K, Kusaka M, Sperelakis N
Department of Physiology and Biophysics, College of Medicine, University of Cincinnati, OH 45267.
Can J Physiol Pharmacol. 1994 Jul;72(7):759-63. doi: 10.1139/y94-108.
The effects of oxytocin (OT) on holding current were studied in uterine smooth muscle cells freshly isolated from the longitudinal layer of 18-20 day pregnant rats, using the nystatin method of whole-cell voltage clamp. As we previously reported, the voltage-dependent Ca2+ current (L type) was partially inhibited by OT (about 30% inhibition at 1 microM). When the cells were held at the holding potential (HP) of -60 mV and the holding current was monitored, OT induced an inward current. The amplitude of this OT-induced current was 72 +/- 26 pA (n = 27). When the cell was held at more positive potentials (HP 0 or +40 mV), the OT-induced current reversed direction, becoming outward. This current usually was long lasting (74% of cells responding to OT); a transient current was observed in 26% of the cells. In the absence of either Na+ or Ca2+ in the bath solution, OT induced an inward current (at HP -60 mV). However, the OT-induced current was absent when both of these ions were omitted from the bath. These results suggest that OT induces an inward current through receptor-activated nonselective cation channels. The resulting increase of intracellular Ca2+ may contribute to the inhibition of voltage-dependent Ca2+ current produced by OT. This OT-induced current may also play an important role for membrane depolarization and accompanying contraction produced by OT in pregnant rat myometrium.
采用制霉菌素全细胞电压钳法，研究了催产素（OT）对从妊娠18 - 20天大鼠子宫纵肌层新鲜分离的子宫平滑肌细胞中保持电流的影响。正如我们之前所报道的，电压依赖性Ca2+电流（L型）受到OT的部分抑制（在1微摩尔时约30%的抑制率）。当细胞保持在-60 mV的保持电位（HP）并监测保持电流时，OT诱导出内向电流。该OT诱导电流的幅度为72±26 pA（n = 27）。当细胞保持在更正的电位（HP为0或+40 mV）时，OT诱导的电流方向反转，变为外向电流。这种电流通常持续时间较长（74%的细胞对OT有反应）；26%的细胞中观察到瞬时电流。在浴液中不存在Na+或Ca2+时，OT诱导出内向电流（在HP为-60 mV时）。然而，当浴液中同时省略这两种离子时，OT诱导的电流消失。这些结果表明，OT通过受体激活的非选择性阳离子通道诱导内向电流。由此导致的细胞内Ca2+增加可能有助于OT对电压依赖性Ca2+电流的抑制。这种OT诱导的电流也可能在OT诱导的妊娠大鼠子宫肌层膜去极化及伴随的收缩中起重要作用。
