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Smooth muscle cholesterol enables BK ?1 subunit-mediated channel inhibition and subsequent vasoconstriction evoked by alcohol.

ABSTRACT: Hypercholesterolemia and alcohol drinking constitute independent risk factors for cerebrovascular disease. Alcohol constricts cerebral arteries in several species, including humans. This action results from inhibition of voltage- and calcium-gated potassium channels (BK) in vascular smooth muscle cells (VSMC). BK activity is also modulated by membrane cholesterol. We investigated whether VSMC cholesterol regulates ethanol actions on BK and cerebral arteries.After myogenic tone development, cholesterol depletion of rat, resistance-size cerebral arteries ablated ethanol-induced constriction, a result that was identical in intact and endothelium-free vessels. Cholesterol depletion reduced ethanol inhibition of BK whether the channel was studied in VSMC or after rat cerebral artery myocyte subunit (cbv1+?1) reconstitution into phospholipid bilayers. Homomeric cbv1 channels reconstituted into bilayers and VSMC BK from ?1 knockout mice were both resistant to ethanol-induced inhibition. Moreover, arteries from ?1 knockout mice failed to respond to ethanol even when VSMC cholesterol was kept unmodified. Remarkably, ethanol inhibition of cbv1+?1 in bilayers and wt mouse VSMC BK were drastically blunted by cholesterol depletion. Consistently, cholesterol depletion suppressed ethanol constriction of wt mouse arteries.VSMC cholesterol and BK ?1 are both required for ethanol inhibition of BK and the resulting cerebral artery constriction, with health-related implications for manipulating cholesterol levels in alcohol-induced cerebrovascular disease.

SUBMITTER: Bukiya AN

PROVIDER: S-EPMC3366592 | biostudies-literature | 2011 Nov

REPOSITORIES: biostudies-literature

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Smooth muscle cholesterol enables BK β1 subunit-mediated channel inhibition and subsequent vasoconstriction evoked by alcohol.

Bukiya Anna N AN Vaithianathan Thirumalini T Kuntamallappanavar Guruprasad G Asuncion-Chin Maria M Dopico Alex M AM

Arteriosclerosis, thrombosis, and vascular biology 20111101 11

<h4>Objective</h4>Hypercholesterolemia and alcohol drinking constitute independent risk factors for cerebrovascular disease. Alcohol constricts cerebral arteries in several species, including humans. This action results from inhibition of voltage- and calcium-gated potassium channels (BK) in vascular smooth muscle cells (VSMC). BK activity is also modulated by membrane cholesterol. We investigated whether VSMC cholesterol regulates ethanol actions on BK and cerebral arteries.<h4>Methods and resu ...[more]

PMID: 21868700

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Project description:In most mammalian tissues, Ca2+i/voltage-gated, large conductance K+ (BK) channels consist of channel-forming slo1 and auxiliary (β1-β4) subunits. When Ca2+i (3-20 µM) reaches the vicinity of BK channels and increases their activity at physiological voltages, β1- and β4-containing BK channels are, respectively, inhibited and potentiated by intoxicating levels of ethanol (50 mM). Previous studies using different slo1s, lipid environments, and Ca2+i concentrations-all determinants of the BK response to ethanol-made it impossible to determine the specific contribution of β subunits to ethanol action on BK activity. Furthermore, these studies measured ethanol action on ionic current under a limited range of stimuli, rendering no information on the gating processes targeted by alcohol and their regulation by βs. Here, we used identical experimental conditions to obtain single-channel and macroscopic currents of the same slo1 channel ("cbv1" from rat cerebral artery myocytes) in the presence and absence of 50 mM ethanol. First, we assessed the role five different β subunits (1,2,2-IR, 3-variant d, and 4) in ethanol action on channel function. Thus, two phenotypes were identified: (1) ethanol potentiated cbv1-, cbv1+β3-, and cbv1+β4-mediated currents at low Ca2+i while inhibiting current at high Ca2+i, the potentiation-inhibition crossover occurring at 20 µM Ca2+i; (2) for cbv1+β1, cbv1+wt β2, and cbv1+β2-IR, this crossover was shifted to ∼3 µM Ca2+i Second, applying Horrigan-Aldrich gating analysis on both phenotypes, we show that ethanol fails to modify intrinsic gating and the voltage-dependent parameters under examination. For cbv1, however, ethanol (a) drastically increases the channel's apparent Ca2+ affinity (nine-times decrease in Kd) and (b) very mildly decreases allosteric coupling between Ca2+ binding and channel opening (C). The decreased Kd leads to increased channel activity. For cbv1+β1, ethanol (a) also decreases Kd, yet this decrease (two times) is much smaller than that of cbv1; (b) reduces C; and (c) decreases coupling between Ca2+ binding and voltage sensing (parameter E). Decreased allosteric coupling leads to diminished BK activity. Thus, we have identified critical gating modifications that lead to the differential actions of ethanol on slo1 with and without different β subunits.

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Smooth muscle cholesterol enables BK ?1 subunit-mediated channel inhibition and subsequent vasoconstriction evoked by alcohol.

Publications

Smooth muscle cholesterol enables BK β1 subunit-mediated channel inhibition and subsequent vasoconstriction evoked by alcohol.

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