Ethanol has different effects on Ca(2+)-transport ATPases of muscle, brain and blood platelets.
The effects of ethanol on different sarco/endoplasmic reticulum Ca(2+)-transport ATPases (SERCAs) were studied. In sarcoplasmic reticulum vesicles, ethanol concentrations varying from 5 to 20% promoted a progressive inhibition of Ca2+ uptake, enhancement of Ca2+ efflux, activation of the ATPase activity, increase of the enzyme phosphorylation by ATP and inhibition of enzyme phosphorylation by P1. The effects of ethanol on Ca2+ uptake and Ca2+ efflux were antagonized by Mg2+, P(i) and spermine. The increased efflux promoted by ethanol was antagonized by Ca2+ and thapsigargin. In brain and platelet vesicles a biphasic effect of ethanol was observed, so that activation occurred at low concentrations (5-10%) and inhibition at higher concentrations. The activation was not observed with the use of n-propanol and n-butanol. Different from the situation in sarcoplasmic reticulum, the decrease of the Ca2+ uptake in brain and platelet vesicles was associated with an inhibition of the ATPase activity. Mg2+ and P(i) antagonized the enhancement of Ca2+ efflux and the inhibition of Ca2+ uptake promoted by ethanol. However, thapsigargin and Ca2+ did not arrest the Ca2+ efflux promoted by ethanol in brain and platelet preparations. These results suggest that, in sarcoplasmic reticulum vesicles, ethanol uncouples the pump, promoting its activity as a Ca2+ channel. The SERCA isoform found in skeletal muscle has different properties from the isoforms found in brain and blood platelets.
Mitidieri
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F
Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, Brazil.
de Meis
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D001921:Brain / Q000201:enzymology*; D002118:Calcium / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000097:blood / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology*; D006868:Hydrolysis; D008274:Magnesium / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000201:enzymology*; D010710:Phosphates / Q000494:pharmacology; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D013096:Spermine / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D004791:Enzyme Inhibitors; D010710:Phosphates; D013729:Terpenes; D013096:Spermine; D000431:Ethanol; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium