Regulation of endothelial BK channels by heme oxygenase-derived carbon monoxide and caveolin-1.

A novel vasodilatory influence of endothelial cell (EC) large-conductance Ca(2+)-activated K(+) (BK) channels is present after in vivo exposure to chronic hypoxia (CH) and may exist in other pathological states. However, the mechanism of channel activation that results in altered vasoreactivity is unknown. Previously, we demonstrated that inhibition of either BK channels or heme oxygenase (HO) restores vasoconstrictor reactivity after CH. Additionally, administration of the scaffolding domain of caveolin (Cav)-1 inhibits EC BK activity and restores vasoconstrictor reactivity in this setting. These results led us to hypothesize that CH exposure results in a loss in Cav-1 inhibition of EC BK channels, resulting in their activation by HO-derived carbon monoxide (CO). Experiments were conducted on freshly dispersed aortic ECs from control and CH-exposed (barometric pressure: 380 mmHg for 48 h) rats. In electrophysiology experiments, outward currents were greater in cells from CH rats as well as from cells from control rats treated with the cholesterol-depleting agent methyl-β-cyclodextrin. These enhanced currents were returned to control by HO inhibition. Channel activity could be restored by the CO donor CO-releasing molecule (CORM)-2 during HO inhibition. Administration of the Cav-1 scaffolding domain eliminated BK currents in cells from CH rats, and current was not restored by the addition of CORM-2. Colocalization experiments in ECs from control and CH rats demonstrated an association between HO-2, Cav-1, and BK. We conclude that EC BK channel activity is HO dependent in the absence of the inhibitory effect of the Cav-1 scaffolding domain.