Schubert R, Krien U, Gagov H
Institute of Physiology, University of Rostock, Germany.
J Vasc Res. 2001 Jan-Feb;38(1):30-8. doi: 10.1159/000051027.
The regulation of the activity of calcium-activated potassium (BK(Ca)) channels by intracellular proton ions (pH(i)) was investigated using the patch-clamp technique in smooth muscle cells freshly isolated from rat tail small arteries. Single-channel conductance and voltage dependence of activation were not different at pH(i) 7.0, 7.4 and 7.8. However, the membrane potential at which channel open probability reached 0.5 was 74 +/- 5 mV (n = 6) (mean +/- SE) at pH(i) 7.4 and 54 +/- 2 mV (n = 4) at pH(i) 7.8 under conditions of pCa 5.9, and 30 +/- 5 mV (n = 5) at pH(i) 7.4 and 62 +/- 4 mV (n = 5) at pH(i) 7.0 under conditions of pCa 5.4. Furthermore, at a membrane potential of 0 mV, the pD(2) for intracellular calcium ions was 5.19 +/- 0.04 (n = 26) (mean +/- SD) at pH(i) 7.8, 5.02 +/- 0.05 (n = 28) at pH(i) 7.4, and 4.82 +/- 0.05 (n = 30) at pH(i) 7.0. In addition, an alteration of pH(i) resulted in a profound change in the amplitude of BK(Ca) currents in intact cells; it reversibly attenuated the current-voltage relationship decreasing the current by 55 +/- 3% (n = 7) (p < 0.001) at 70 mV after lowering the extracellular NH(4)Cl concentration to decrease the calculated pH(i) from 7.2 to 6.8. Thus, alterations of pH(i) in the range from 7.0 to 7.8 did not affect single-channel conductance and voltage dependence of activation but markedly altered single BK(Ca) channel activity as well as intact cell BK(Ca) current amplitude, where an increase of the intracellular proton concentration inhibited this channel.
采用膜片钳技术，在从大鼠尾小动脉新鲜分离的平滑肌细胞中研究了细胞内质子（pH(i)）对钙激活钾（BK(Ca)）通道活性的调节作用。在pH(i) 7.0、7.4和7.8时，单通道电导和激活的电压依赖性没有差异。然而，在pCa 5.9的条件下，pH(i) 7.4时通道开放概率达到0.5的膜电位为74±5 mV（n = 6）（平均值±标准误），pH(i) 7.8时为54±2 mV（n = 4）；在pCa 5.4的条件下，pH(i) 7.4时为30±5 mV（n = 5），pH(i) 7.0时为62±4 mV（n = 5）。此外，在膜电位为0 mV时，pH(i) 7.8时细胞内钙离子的pD(2)为5.19±0.04（n = 26）（平均值±标准差），pH(i) 7.4时为5.02±0.05（n = 28），pH(i) 7.0时为4.82±0.05（n = 30）。另外，pH(i)的改变导致完整细胞中BK(Ca)电流幅度发生显著变化；在降低细胞外NH(4)Cl浓度以将计算出的pH(i)从7.2降至6.8后，在70 mV时电流-电压关系可逆性减弱，电流降低了55±3%（n = 7）（p < 0.001）。因此，pH(i)在7.0至7.8范围内的改变不影响单通道电导和激活的电压依赖性，但显著改变了单个BK(Ca)通道活性以及完整细胞BK(Ca)电流幅度，其中细胞内质子浓度的增加会抑制该通道。
