Ethanol and inositol 1,4,5-trisphosphate release calcium from separate stores of brain microsomes.
The effects of ethanol and inositol 1,4,5-trisphosphate (IP3) on releasable Ca stores were examined in microsomes isolated from mouse whole brain. Ca release was monitored by determination of changes in the extra-microsomal Ca concentration using Indo-1, a fluorescent Ca indicator. In the absence of ATP, ethanol released Ca from microsomes in a concentration-dependent manner, with a threshold for Ca release between 25 and 50 mM. Ethanol-induced release of microsomal Ca was reduced by approximately 50% after ATP-stimulated uptake of Ca, indicating that the ethanol-releasable pool was diminished by ATP-dependent uptake of Ca into an ethanol-insensitive microsomal pool. Release of Ca produced by ethanol was linear with concentration (up to 400 mM). By contrast, IP3-induced Ca release was saturable and was dependent on prior ATP-stimulated Ca uptake. Simultaneous addition of ethanol and IP3 produced additive responses. These results show that pharmacologically relevant concentrations of ethanol release Ca from an IP3-insensitive intracellular Ca store. Furthermore, our results demonstrate the existence of at least two releasable stores of Ca in brain microsomes.
Department of Pharmacology, University of Colorado Health Sciences Center, Denver.
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LC
Daniell
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Harris
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051379:Mice; D008861:Microsomes / Q000378:metabolism; D013403:Sugar Phosphates / Q000494:pharmacology*; D013696:Temperature; D014639:Vanadium / Q000494:pharmacology
D007295:Inositol Phosphates; D013403:Sugar Phosphates; D014639:Vanadium; D000431:Ethanol; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D002118:Calcium