The chemical modification of KCa channels by carbon monoxide in vascular smooth muscle cells.
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.
Wang
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Research Centre of Hôpital du Sacré-Coeur de Montréal and the Département de physiologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada.
Wu
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L
D000818:Animals; D002248:Carbon Monoxide / Q000494:pharmacology*; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010084:Oxidation-Reduction; D010777:Photochemistry; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D051381:Rats
D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D002248:Carbon Monoxide; D004047:Diethyl Pyrocarbonate