Somatic Localization of a Specific Large-Conductance Calcium-Activated Potassium Channel Subtype Controls Compartmentalized Ethanol Sensitivity in the Nucleus Accumbens

Abstract

Alcohol is an addictive drug that targets a variety of ion channels and receptors. To address whether the effects of alcohol are compartment specific (soma vs dendrite), we examined the effects of ethanol (EtOH) on large-conductance calcium-activated potassium channels (BK) in cell bodies and dendrites of freshly isolated neurons from the rat nucleus accumbens (NAcc), a region known to be critical for the development of addiction. Compartment-specific drug action was indeed observed. Clinically relevant concentrations of EtOH increased somatic but not dendritic BK channel open probability. Electrophysiological single-channel recordings and pharmacological analysis of the BK channel in excised patches from each region indicated a number of differences, suggestive of a compartment-specific expression of the ␤4 subunit of the BK channel, that might explain the differential alcohol sensitivity. These parameters included activation kinetics, calcium dependency, and toxin blockade. Reverse transcription-PCR showed that both BK channel ␤1 and ␤4 subunit mRNAs are found in the NAcc, although the signal for ␤1 is significantly weaker. Immunohistochemistry revealed that ␤1 subunits were found in both soma and dendrites, whereas ␤4 appeared restricted to the soma. These findings suggest that the ␤4 subunit may confer EtOH sensitivity to somatic BK channels, whereas the absence of ␤4 in the dendrite results in insensitivity to the drug. Consistent with this idea, acute EtOH potentiated ␣␤4 BK currents in transfected human embryonic kidney cells, whereas it failed to alter ␣␤1 BK channel-mediated currents. Finally, an EtOH concentration (50 mM) that increased BK channel open probability strongly decreased the duration of somatic-generated action potential in NAcc neurons.

Identification of a BK channel auxiliary protein controlling molecular and behavioral tolerance to alcohol

“…50 mM EtOH, a concentration known to strongly influence channel activity (19), increased ␣␤4 BK channel open probability ( Fig. 1A; middle trace EtOH 3 min) compared to control (Fig.…”

“…Recently, we also reported that EtOH effects depend on BK channel subunit composition in ventral striatum. We found that ␣␤4 BK channels were potentiated by EtOH, whereas ␣␤1 channels were not (19). In the present study, we tested the hypothesis that BK subunit composition can control the degree and duration of ethanol sensitivity and, because of robust expression in striatum-a brain region implicated in addiction-we predicted that differences in BK subunit expression can translate into altered ethanolinduced behaviors.…”

“…Whereas ␤1 expression is found at low levels in brain, ␤2 and ␤3 do not appear to be expressed in the central nervous system (16,17). In previous work, we showed that low EtOH concentrations (10-50 mM) potentiated BK channel open probability in a number of brain regions (hypothalamo-hypophyseal axis and nucleus accumbens) (18)(19)(20). Recently, we also reported that EtOH effects depend on BK channel subunit composition in ventral striatum.…”

Low-Dose Ethanol Preconditioning Protects Against Oxygen-Glucose Deprivation/Reoxygenation-Induced Neuronal Injury By Activating Large Conductance, Ca2+-Activated K+ Channels In Vitro

“…For example, ethanol decreases the excitability of neurons in rat dorsal root ganglia by activating the BK Ca channel, and this is associated with ethanol-related analgesia [44]. In rat nucleus accumbens neurons, ethanol accelerates the action potential repolarization by activating the BK Ca channel [45]. In cultured human umbilical vein endothelial cells, 10 and 50 mmol/L ethanol directly activate BK Ca channels, leading to increased endothelial proliferation, indicating a possible beneficial effect of ethanol on endothelial function [20].…”

GABAA receptor subtypes: the “one glass of wine” receptors

“…Further open questions are the interesting connection of alcohol actions with the adenosine receptors (Dar et al, 1983;Choi et al, 2004;Dar, 2006), protein kinases (Hodge et al, 1999;Proctor et al, 2003;Wallace et al, 2007), NMDA and AMPA receptors (Lovinger et al, 1989;Woodward, 2000), BK channels (Martin et al, 2004;Cowmeadow et al, 2006), glycine receptors (Davies et al, 2003), K v + channels (Espinosa et al, 2001), and the modulation of alcohol actions via G protein-coupled receptors (Wan et al, 1996;Nie et al, 2004;Besheer et al, 2006) as well as the molecular mechanism behind of the fascinating observation of behavioral alcohol antagonism by pressure (Alkana et al, 1985;Davies and Alkana, 2001). The challenge is to find answers to these and many more important questions in the future and to integrate these findings into an increasingly comprehensive picture on which the majority of us can agree.…”