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Molecular Tolerance of Voltage‐Gated Calcium Channels is Evident After Short Exposures to Alcohol in Vasopressin‐Releasing Nerve Terminals
Author(s) -
Pietrzykowski Andrzej Z.,
OrtizMiranda Sonia,
Knott Thomas K.,
Custer Edward,
Puig Sylvie,
Lemos José R.,
Treistman Steven N.
Publication year - 2013
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/acer.12057
Subject(s) - vasopressin , alcohol , electrophysiology , voltage dependent calcium channel , desensitization (medicine) , ethanol , calcium , patch clamp , chemistry , endocrinology , medicine , explant culture , biophysics , in vitro , biology , biochemistry , receptor
Background Voltage‐gated calcium channels ( VGCC s) in rat neurohypophysial terminals exhibit molecular tolerance to alcohol, including desensitization to the drug and increased current density, after 3 weeks of alcohol drinking. Moreover, after this time, terminals from drinking rats exhibit diminished alcohol inhibition of vasopressin ( AVP ) release. Methods We took advantage of organotypic cultures (explants) of the hypothalamo‐neurohypophysial system ( HNS ) to extend our analysis of molecular tolerance to 2 classes of the VGCC . The isolated HNS explant allows much finer temporal resolution of molecular tolerance than do voluntary drinking paradigms. After exposure of the HNS explant to alcohol, terminals are isolated by mechanical treatment and plated in a dish. Patch clamp recording techniques are used to obtain VGCC currents, and immunohistochemistry is used to determine VGCC distribution. A release assay is used to provide functional readout of AVP release. Results We show that even a brief, 1‐hour exposure to a clinically relevant concentration of alcohol is sufficient to evoke similar changes to those observed after several weeks of exposure. Acute ethanol ( E t OH ) exposure inhibits high K + ‐induced AVP release from naïve terminals. However, terminals pre‐exposed to 20 mM E t OH for 1 hour become tolerant to E t OH , and subsequent exposure has significantly less effect on high K + ‐induced AVP release. Electrophysiological recordings indicate that among different types of VGCC s present in the neuronal terminal, the L ‐type is the most affected by alcohol. The current density of L ‐type current is significantly increased (approximately 50%), while its responsiveness to alcohol is significantly diminished (approximately 50%), after brief alcohol exposure. Fluorescent imaging results were consistent with the electrophysiology and suggest that the increased current density of VGCC s after brief exposure is attributable to combined synthesis of 1.2 and 1.3 subtypes of the L ‐type VGCC and redistribution of channel protein into terminal plasma membrane. Conclusions These data indicate that a brief alcohol exposure affects subsequent alcohol sensitivity of VGCC s and neuropeptide release from presynaptic terminals.