Obejero-Paz C A, Jones S W, Scarpa A
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Biophys J. 1998 Sep;75(3):1271-86. doi: 10.1016/S0006-3495(98)74047-0.
Ca2+ entry under resting conditions may be important for contraction of vascular smooth muscle, but little is known about the mechanisms involved. Ca2+ leakage was studied in the A7r5 smooth muscle-derived cell line by patch-clamp techniques. Two channels that could mediate calcium influx at resting membrane potentials were characterized. In 110 mM Ba2+, one channel had a slope conductance of 6.0 +/- 0.6 pS and an extrapolated reversal potential of +41 +/- 13 mV (mean +/- SD, n = 8). The current rectified strongly, with no detectable outward current, even at +90 mV. Channel gating was voltage independent. A second type of channel had a linear current-voltage relationship, a slope conductance of 17.0 +/- 3.2 pS, and a reversal potential of +7 +/- 4 mV (n = 9). The open probability increased e-fold per 44 +/- 10 mV depolarization (n = 5). Both channels were also observed in 110 mM Ca2+. Noise analysis of whole-cell currents indicates that approximately 100 6-pS channels and 30 17-pS channels are open per cell. These 6-pS and 17-pS channels may contribute to resting calcium entry in vascular smooth muscle cells.
静息状态下的Ca2+内流对于血管平滑肌的收缩可能很重要，但其中涉及的机制却知之甚少。通过膜片钳技术在A7r5平滑肌衍生细胞系中研究了Ca2+泄漏情况。鉴定出了两种可在静息膜电位介导钙内流的通道。在110 mM Ba2+中，一种通道的斜率电导为6.0±0.6 pS，外推反转电位为+41±13 mV（平均值±标准差，n = 8）。电流强烈整流，即使在+90 mV时也未检测到外向电流。通道门控与电压无关。第二种通道具有线性电流-电压关系，斜率电导为17.0±3.2 pS，反转电位为+7±4 mV（n = 9）。每44±10 mV去极化，开放概率增加e倍（n = 5）。在110 mM Ca2+中也观察到了这两种通道。全细胞电流的噪声分析表明，每个细胞约有100个6-pS通道和30个17-pS通道开放。这些6-pS和17-pS通道可能有助于血管平滑肌细胞的静息钙内流。
