Cholesterol-ethanol Interactions On Vascular Myocyte BK Channels: Contribution To Alcohol-induced Cerebrovascular Constriction

Abstract

The activity of large conductance, calcium- and voltage-gated potassium (BK) channels critically limits the degree of vascular smooth muscle contraction, favoring cerebrovascular dilation (Brayden and Nelson, 1992). Ethanol at levels reached in circulation after moderate binge drinking (50 mM) inhibits the activity of cerebrovascular myocyte BK channels, leading to endothelium-independent cerebrovascular constriction (Liu et al., 2004). On the other hand, high cholesterol levels, which inhibit vascular smooth muscle BK channels (Bolotina et al., 1989), decrease vascular compliance, favoring vasoconstriction (Bukiya et al., 2008). Synergistic inhibition of cerebrovascular BK channels by cholesterol and ethanol would certainly have a profound negative impact on vascular compliance and dilation. Remarkably, such synergism on channel function has not been studied. Thus, we cloned BK subunits (channel-forming cbv1 and accessory, smooth muscle-abundant β1) from rat resistance-size cerebral arteries, reconstituted the channel complex into 1-palmitoyl-2-oleoyl phosphatidylethanolamine/1-palmitoyl-2-oleoyl phosphatidylserine (POPE/POPS) bilayers, and studied cholesterol modulation of ethanol action on channel steady-state activity (NPo). Acute exposure to 50 mM ethanol mildly yet significantly decreased BK NPo (−4 ± 0.8 % from control) without modifying channel unitary conductance. In the same bilayer type, incorporation of cholesterol at levels found in cell membranes (15 % w/w) also reduced BK NPo (-8.78 ± 5.2 % from control). Remarkably, 50 mM EtOH added to the cholesterol-containing bilayer resulted in a robust decrease in BK NPo (−36 ± 8.4 % from control). These data unveil a multiplicative inhibition of BK channel activity by alcohol and cholesterol. The kinetic and biophysical mechanisms of such synergism are currently being investigated.