Rodríguez-Contreras Adrián, Yamoah Ebenezer N
Center for Neuroscience, Department of Otolaryngology, University of California at Davis, 1544 Newton Court, Davis, CA 95616, USA.
Biophys J. 2003 May;84(5):3457-69. doi: 10.1016/S0006-3495(03)70066-6.
We determined the gating and permeation properties of single L-type Ca(2+) channels, using hair cells and varying concentrations (5-70 mM) of the charge carriers Ba(2+) and Ca(2+). The channels showed distinct gating modes with high- and low-open probability. The half-activation voltage (V(1/2)) shifted in the hyperpolarizing direction from high to low permeant ion concentrations consistent with charge screening effects. However, the differences in the slope of the voltage shifts (in VM(-1)) between Ca(2+) (0.23) and Ba(2+) (0.13), suggest that channel-ion interaction may also contribute to the gating of the channel. We examined the effect of mixtures of Ba(2+) and Ca(2+) on the activation curve. In 5 mM Ca(2+), the V(1/2) was, -26.4 +/- 2.0 mV compared to Ba(2+), -34.7 +/- 2.9 mV, as the charge carrier. However, addition of 1 mM Ba(2+) in 4 mM Ca(2+), a molar ratio, which yielded an anomalous-mole fraction effect, was sufficient to shift the V(1/2) to -34.7 +/- 1.5 mV. Although Ca(2+)-dependent inactivation of the L-type channels in hair cells can yield the present findings, we provide evidence that the anomalous gating of the channel may stem from the closed interaction between ion permeation and gating.
我们使用毛细胞以及不同浓度（5 - 70 mM）的载流子Ba(2+)和Ca(2+)，确定了单个L型Ca(2+)通道的门控和通透特性。这些通道呈现出具有高开放概率和低开放概率的不同门控模式。半激活电压（V(1/2)）随着通透离子浓度从高到低而向超极化方向移动，这与电荷筛选效应一致。然而，Ca(2+)（0.23）和Ba(2+)（0.13）之间电压偏移斜率（以VM(-1)为单位）的差异表明，通道 - 离子相互作用也可能对通道的门控有贡献。我们研究了Ba(2+)和Ca(2+)混合物对激活曲线的影响。在5 mM Ca(2+)中，作为载流子，V(1/2)为 - 26.4 ± 2.0 mV，而对于Ba(2+)为 - 34.7 ± 2.9 mV。然而，在4 mM Ca(2+)中添加1 mM Ba(2+)（一种产生异常摩尔分数效应的摩尔比）足以将V(1/2)移至 - 34.7 ± 1.5 mV。虽然毛细胞中L型通道的Ca(2+)依赖性失活可以产生当前的发现，但我们提供证据表明，通道的异常门控可能源于离子通透和门控之间的紧密相互作用。
