Alcohol Tolerance in Large-Conductance, Calcium-Activated Potassium Channels of CNS Terminals Is Intrinsic and Includes Two Components: Decreased Ethanol Potentiation and Decreased Channel Density

Abstract

Tolerance is an important element of drug addiction and provides a model for understanding neuronal plasticity. The hypothalamicneurohypophysial system (HNS) is an established preparation in which to study the actions of alcohol. Acute application of alcohol to the rat neurohypophysis potentiates large-conductance calcium-sensitive potassium channels (BK), contributing to inhibition of hormone secretion. A cultured HNS explant from adult rat was used to explore the molecular mechanisms of BK tolerance after prolonged alcohol exposure. Ethanol tolerance was intrinsic to the HNS and consisted of: (1) decreased BK potentiation by ethanol, complete within 12 min of exposure, and (2) decreased current density, which was not complete until 24 hr after exposure, indicating that the two components of tolerance represent distinct processes. Single-channel properties were not affected by chronic exposure, suggesting that decreased current density resulted from downregulation of functional channels in the membrane. Indeed, we observed decreased immunolabeling against the BK ␣-subunit on the surface of tolerant terminals. Analysis using confocal microscopy revealed a reduction of BK channel clustering, likely associated with the internalization of the channel.

Compartmentalized β Subunit Distribution Determines Characteristics and Ethanol Sensitivity of Somatic, Dendritic, and Terminal Large-Conductance Calcium-Activated Potassium Channels in the Rat Central Nervous System

“…In contrast, EtOH greatly potentiated the activity of channels in dissociated nerve terminals in a dose-dependent fashion. The peak effect was observed with 50 mM EtOH (673 Ϯ 171%, n ϭ 3), consistent with previous data (Dopico et al, 1996;Pietrzykowski et al, 2004) (Fig. 4, C and D).…”

BK channels play a counter-adaptive role in drug tolerance and dependence

“…Recent studies to investigate the physiological mechanism of ethanol tolerance in the rat hypothalamic neurohypophysial explant model system show evidence of reduced BK channel expression following ethanol exposure. In these studies, the explant is chronically exposed to ethanol, which causes a reduction in BK channel density through the internalization of membrane channels and the down-regulation of ethanol-sensitive BK isoforms caused by microRNA degradation of selected mRNA splice variants (33,34). These results contrast with the alcohol/anesthetic-induced increase in BK channel expression that we observe in Drosophila (5, 6).…”

In vitroandin vivomodels of acute alcohol exposure

“…Most of the in vitro research involves culture of a single cell type [134,[139][140][141][142] or co-culture of several cell types [143] ; while such an approach brings forward the differential effect of alcohol on pure cell populations, and/or their intercellular interaction; it lacks the systemic alcohol metabolism and intercellular interactions. More recently significant efforts were invested in establishment of more complex in vitro systems, such as culture of cells in three dimensional systems [100] , organ slices [144] or organ explants [145] ; while such systems are informative in the setting of chronic alcohol exposure to date there is no report of their use as an AAA model.…”