Received for publication May 8, 2008.
Revised June 12, 2008.
Accepted for publication June 13, 2008.

Ethanol modulates BK_Ca channels by acting as an adjuvant of calcium

Abstract

Ethanol modulation of calcium- and voltage-gated potassium (slo1) channels alters neuronal excitability, cerebrovascular tone, brain function and behavior, yet the mechanism of this modulation remains unknown. Using patch-clamp electrophysiology on recombinant BK_Ca channels cloned from mouse brain and expressed in Xenopus oocytes, we demonstrate that ethanol, even at concentrations maximally effective to modulate BK_Ca channel function (100 mM), fails to gate the channel in absence of activating calcium. Moreover, ethanol does not modify intrinsic, voltage- or physiological magnesium-driven gating. The alcohol works as an adjuvant of calcium by selectively facilitating calcium-driven gating. This facilitation, however, renders differential ethanol effects on channel activity: potentiation at low (<10 µM) and inhibition at high (>10 µM) calcium, this dual pattern remaining largely unmodified by co-expression of brain slo1 channels with the neuronally-abundant BK_Ca channel beta4 subunit. Calcium recognition by either of the slo1 high-affinity sensors (calcium bowl and RCK1 D362/D367) is required for ethanol to amplify channel activation by calcium. The D362/D367 site, however, is necessary and sufficient to sustain ethanol inhibition. This inhibition also results from ethanol facilitation of calcium action; in this case, ethanol favors channel dwelling in a calcium-driven, low-activity mode. The agonist-adjuvant mechanism that we advance from the calcium-ethanol interaction on slo1 might be applicable to data of ethanol action on a wide variety of ligand-gated channels.

Key words: Ion channel regulation, Calcium (Votage-Gated Channels), Molecular dynamics, Func. analysis receptor/ion channel mutants, Mutagenesis/Chimeric approaches, Single channel kinetics, Alcohol, Alcohols