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HEME OXYGENASE

Interaction of Selective Amino Acid Residues of K_Ca Channels with Carbon Monoxide

Department of Physiology, Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5E5

Abstract

The activation of big-conductance K_Ca channels in vascular smooth muscle cells by carbon monoxide (CO) has been demonstrated previously. One specific target of CO on K_Ca channel proteins is the histidine residue. The roles of other amino acid residues on the functionality of K_Ca channels, as well as their reactions to CO, have been unclear. In the present study, the cell-free single channel recording technique was used to investigate the chemical modification of K_Ca channels by CO and other chemical agents. The modification of negatively charged carboxyl groups and the -amino group of lysine did not affect the open probability, but decreased single-channel conductance of K_Ca channels. When sulfhydryl groups of cysteine were modified with N-ethylmaleimide, the open probability of K_Ca channels was decreased, but single-channel conductance was not affected. None of the above chemical modifications affected the CO-induced increase in the open probability of K_Ca channels. However, N-ethylmaleimide treatment reduced the stimulatory effect of nitric oxide (NO) on K_Ca channels. Finally, pretreatment of smooth muscle cells with NO abolished the effects of subsequently applied CO on K_Ca channel proteins. Our study demonstrates that CO and NO acted on different amino acid residues of K_Ca channel proteins. The interaction of CO and NO determines the functional status of K_Ca channels in vascular smooth muscle cells

Key Words: carbon monoxide • chemical modification • gasotransmitter • K_Ca channels • nitric oxide

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