Wang R, Wu L
Research Centre of Hôpital du Sacré-Coeur de Montréal and the Département de physiologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada.
J Biol Chem. 1997 Mar 28;272(13):8222-6. doi: 10.1074/jbc.272.13.8222.
The chemical modification of big conductance calcium-activated potassium (KCa) channels in rat tail artery smooth muscle cells by carbon monoxide (CO) was investigated using the cell-free single channel recording technique. Exposure of the internal surface of cell membranes to diethyl pyrocarbonate (DEPC) neither affected the characteristics of KCa channels nor modified the stimulatory effect of CO on KCa channels. However, when DEPC was applied to the external surface of cell membranes, the open probability of KCa channels was reduced. The pH and concentration dependence of the effect of DEPC indicated the specific modification of histidine residues. Kinetic analysis suggested that one externally located histidine residue was modified by DEPC. Treatment of the external surface of cell membranes with DEPC abolished the CO-induced increase in the open probability of KCa channels. Likewise, the presence of CO partially protected KCa channels from inhibition by DEPC. Moreover, photooxidation of the histidine residue located on the external membrane surface abolished the CO-induced activation of KCa channels. Our study demonstrates that the CO-induced increase in the open probability of KCa channels may rely specifically on the structure and topological locations of histidine residues.
采用无细胞单通道记录技术，研究了一氧化碳（CO）对大鼠尾动脉平滑肌细胞中大电导钙激活钾（KCa）通道的化学修饰作用。用焦碳酸二乙酯（DEPC）处理细胞膜内表面，既不影响KCa通道的特性，也不改变CO对KCa通道的刺激作用。然而，当将DEPC应用于细胞膜外表面时，KCa通道的开放概率降低。DEPC作用的pH值和浓度依赖性表明其对组氨酸残基具有特异性修饰作用。动力学分析表明，一个位于细胞外的组氨酸残基被DEPC修饰。用DEPC处理细胞膜外表面可消除CO诱导的KCa通道开放概率增加。同样，CO的存在可部分保护KCa通道免受DEPC的抑制。此外，对位于细胞膜外表面的组氨酸残基进行光氧化可消除CO诱导的KCa通道激活。我们的研究表明，CO诱导的KCa通道开放概率增加可能特别依赖于组氨酸残基的结构和拓扑位置。
