Interaction of selective amino acid residues of KCa channels with carbon monoxide

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 E-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.