Dataset Information

Time-Dependent Effects of Ethanol on BK Channel Expression and Trafficking in Hippocampal Neurons.

ABSTRACT: The large conductance Ca(2+) - and voltage-activated K(+) channel (BK) is an important player in molecular and behavioral alcohol tolerance. Trafficking and surface expression of ion channels contribute to the development of addictive behaviors. We have previously reported that internalization of the BK channel is a component of molecular tolerance to ethanol (EtOH).Using primary cultures of hippocampal neurons, we combine total internal reflection fluorescence microscopy, electrophysiology, and biochemical techniques to explore how exposure to EtOH affects the expression and subcellular localization of endogenous BK channels over time.Exposure to EtOH changed the expression of endogenous BK channels in a time-dependent manner at the perimembrane area (plasma membrane and/or the area adjacent to it), while total protein levels of BK remain unchanged. These results suggest a redistribution of the channel within the neurons rather than changes in synthesis or degradation rates. Our results showed a temporally nonlinear effect of EtOH on perimembrane expression of BK. First, there was an increase in BK perimembrane expression after 10 minutes of EtOH exposure that remained evident after 3 hours, although not correlated to increases in functional channel expression. In contrast, after 6 hours of EtOH exposure, we observed a significant decrease in both BK perimembrane expression and functional channel expression. Furthermore, after 24 hours of EtOH exposure, perimembrane levels of BK had returned to baseline.We report a complex time-dependent pattern in the effect of EtOH on BK channel trafficking, including successive increases and decreases in perimembrane expression and a reduction in active BK channels after 3 and 6 hours of EtOH exposure. Possible mechanisms underlying this multiphasic trafficking are discussed. As molecular tolerance necessarily underlies behavioral tolerance, the time-dependent alterations we see at the level of the channel may be relevant to the influence of drinking patterns on the development of behavioral tolerance.

SUBMITTER: Palacio S

PROVIDER: S-EPMC4873156 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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Time-Dependent Effects of Ethanol on BK Channel Expression and Trafficking in Hippocampal Neurons.

Palacio Stephanie S Velázquez-Marrero Cristina C Marrero Héctor G HG Seale Garrett E GE Yudowski Guillermo A GA Treistman Steven N SN

Alcoholism, clinical and experimental research 20150806 9

<h4>Background</h4>The large conductance Ca(2+) - and voltage-activated K(+) channel (BK) is an important player in molecular and behavioral alcohol tolerance. Trafficking and surface expression of ion channels contribute to the development of addictive behaviors. We have previously reported that internalization of the BK channel is a component of molecular tolerance to ethanol (EtOH).<h4>Methods</h4>Using primary cultures of hippocampal neurons, we combine total internal reflection fluorescence ...[more]

PMID: 26247146

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Project description:Large conductance calcium-activated potassium (BK) channels play a key role in the control of neuronal activity. Ethanol is a potent activator of BK channel gating, but how this action may impact ethanol drinking still remains poorly understood. Auxiliary β subunits are known to modulate ethanol-induced potentiation of BK currents. In the present study, we investigated whether BK β1 and β4 subunits influence voluntary ethanol consumption using knockout (KO) mice. In a first experiment, mice were first subjected to continuous two-bottle choice (2BC) and were then switched to intermittent 2BC, which progressively increased ethanol intake as previously described in wildtype mice. BK β1 or β4 subunit deficiency did not affect ethanol self-administration under either schedule of access. In a second experiment, mice were first trained to drink ethanol in a limited-access 2BC paradigm. BK β1 or β4 deletion did not affect baseline consumption. Weeks of 2BC were then alternated with weeks of chronic intermittent ethanol (CIE) or air inhalation. As expected, a gradual escalation of ethanol drinking was observed in dependent wildtype mice, while intake remained stable in non-dependent wildtype mice. However, CIE exposure only produced a mild augmentation of ethanol consumption in BK β4 KO mice. Conversely, ethanol drinking increased after fewer CIE cycles in BK β1 KO mice than in wildtype mice. In conclusion, BK β1 or β4 did not influence voluntary ethanol drinking in non-dependent mice, regardless of the pattern of access to ethanol. However, deletion of BK β4 attenuated, while deletion of BK β1 accelerated, the escalation of ethanol drinking during withdrawal from CIE. Our data suggest that BK β1 and β4 subunits have an opposite influence on the negative reinforcing properties of ethanol withdrawal. Modulating the expression, distribution or interactions of BK channel auxiliary subunits may therefore represent a novel avenue for the treatment of alcoholism.

Project description:The importance and diversity of calcium signaling in the brain is mirrored by the expression of a multitude of voltage-activated calcium channel (Ca(V)) isoforms. Whereas the overall distributions of alpha(1) subunits are well established, the expression patterns of distinct channel isoforms in specific brain regions and neurons, as well as those of the auxiliary beta and alpha(2)delta subunits are still incompletely characterized. Further it is unknown whether neuronal differentiation and activity induce changes of Ca(V) subunit composition. Here we combined absolute and relative quantitative TaqMan reverse transcription PCR (RT-PCR) to analyze mRNA expression of all high voltage-activated Ca(V) alpha(1) subunits and all beta and alpha(2)delta subunits. This allowed for the first time the direct comparison of complete Ca(V) expression profiles of mouse cortex, hippocampus, cerebellum, and cultured hippocampal neurons. All brain regions expressed characteristic profiles of the full set of isoforms, except Ca(V)1.1 and Ca(V)1.4. In cortex development was accompanied by a general down regulation of alpha(1) and alpha(2)delta subunits and a shift from beta(1)/beta(3) to beta(2)/beta(4). The most abundant Ca(V) isoforms in cerebellum were Ca(V)2.1, beta(4), and alpha(2)delta-2, and in hippocampus Ca(V)2.3, beta(2), and alpha(2)delta-1. Interestingly, cultured hippocampal neurons also expressed the same Ca(V) complement as adult hippocampus. During differentiation specific Ca(V) isoforms experienced up- or down-regulation; however blocking electrical activity did not affect Ca(V) expression patterns. Correlation analysis of alpha(1), beta and alpha(2)delta subunit expression throughout all examined preparations revealed a strong preference of Ca(V)2.1 for beta(4) and alpha(2)delta-2 and vice versa, whereas the other alpha(1) isoforms were non-selectively expressed together with each of the other beta and alpha(2)delta isoforms. Together our results revealed a remarkably stable overall Ca(2+) channel complement as well as tissue specific differences in expression levels. Developmental changes are likely determined by an intrinsic program and not regulated by changes in neuronal activity.

Dataset Information

Time-Dependent Effects of Ethanol on BK Channel Expression and Trafficking in Hippocampal Neurons.

Publications

Time-Dependent Effects of Ethanol on BK Channel Expression and Trafficking in Hippocampal Neurons.

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