Possible association of alcohol tolerance with increased synaptic Ca2+ sensitivity.
The inhibitory effect of ethanol on neurotransmitter release has been suggested to be due to either reduced Ca2+ entry or increased removal of free intracellular Ca2+ from the synapse. The use of the Ca2+ ionophore, A23187, to allow direct access of external Ca2+ to the presynaptic interior should help to determine which of these two factors is the more important, as ethanol should inhibit A23187-induced release of transmitter only if increased Ca2+ removal from the synapse is important. Here we show in rat striatal slices that, although 3H-dopamine release evoked by depolarization with 40 mM K+ is inhibited by 50 mM ethanol, the release evoked by A23187 is enhanced by the presence of ethanol in vitro. The results suggest that ethanol reduces depolarization-induced transmitter release by reducing Ca2+ entry to the presynaptic terminal. However, for brain slices taken from rats made tolerant to ethanol, 3H-dopamine release in the absence of ethanol showed altered characteristics; both K+ depolarization and A23187 released a significantly greater fraction of 3H-dopamine from these slices than from controls. Thus tolerance to the inhibitory effect of ethanol on release may develop by a mechanism involving increased sensitivity of the terminal to Ca2+ entry.
D000437:Alcoholism / Q000503:physiopathology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D003342:Corpus Striatum / Q000502:physiology; D004195:Disease Models, Animal; D004298:Dopamine / Q000378:metabolism; D004361:Drug Tolerance; D000431:Ethanol / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D011188:Potassium / Q000502:physiology; D051381:Rats; D009435:Synaptic Transmission / Q000187:drug effects*
D000431:Ethanol; D011188:Potassium; D002118:Calcium; D004298:Dopamine