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.
Daniell
L C
LC
Department of Pharmacology, University of Colorado Health Sciences Center, Denver.
Harris
R A
RA
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