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

Abstract

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.

Hydrogen sulfide dilates rat mesenteric arteries by activating endothelial large-conductance Ca2+-activated K+ channels and smooth muscle Ca2+ sparks

“…We have described differences in Ca 2ϩ sensitivity of BK Ca channels in EC and VSMC (23,24), directly demonstrating potential differences in regulation of BK Ca channels in these two cell types. Specifically, EC BK Ca channels display a greater Ca 2ϩ sensitivity despite the apparent lack of functional BK-␤1 subunits, and H 2 S may affect the moiety responsible for this difference.…”

Gas Signaling Molecules and Mitochondrial Potassium Channels

“…In several studies, it was shown that BK Ca channels are strongly activated by CORM-2 or CORM-3 [ 91 , 92 , 93 , 94 ] and that different regions that are unrelated to the heme binding motif (HBM) were implicated in this phenomenon [ 95 , 96 ]. Specifically, the stimulatory action of CORM-2 on BK Ca channels required the presence of an aspartic acid and two histidine residues (365 and 394) in the cytoplasmic RCK1 domain [ 96 ].…”

Regulation of Cellular Communication by Signaling Microdomains in the Blood Vessel Wall

“…Although both HO-1 and HO-2 are primarily found in the endoplasmic reticulum (e.g., Tenhunen et al, 1968), there is now sufficient evidence that both enzymes can associate with Cav1 at the plasma membrane of mesengial (Jung et al, 2003) and endothelial cells . Further reports indicated that Cav1 is a competitive inhibitor for HO-1, identifying a minimum sequence required for binding (Taira et al, 2011) and possibly regulating activation of BKCa channels in endothelium (Riddle and Walker, 2012) [although this Cav1 interaction has yet to be detected in smooth muscle cells where the link between BK and CO was originally identified and well-described (Wang et al, 1997;Jaggar et al, 2002Jaggar et al, , 2005Xi et al, 2004)]. One report indicated that cytochrome P450 reductase is also associated with Cav1 (Jung et al, 2003), potentially forming a compartmentalized signaling microdomain for CO production.…”