Uncoupling of Ca2+ transport ATPase in muscle and blood platelets by diacylglycerol analogues and cyclosporin A antagonism.
The possibility that diacylglycerol analogues might have a wider spectrum of intracellular targets than the well-known protein kinase C was investigated with vesicles containing the Ca2+-ATPase derived from the dense tubular system in platelets and from the sarcoplasmic reticulum of skeletal muscle. The diacylglycerol analogues PMA and 1-oleoyl-2-acetyl-rac-glycerol (OAG) inhibited Ca2+ accumulation by these vesicles, an effect that was antagonized by cyclosporin A. The inhibitory activity of PMA and OAG resulted from the uncoupling of the Ca2+-ATPase, characterized by a pronounced inhibition of Ca2+ uptake accompanied by a discrete decrease in ATPase activity and by the inhibition of the enzyme's phosphorylation by Pi, leading to both a decrease in ATP synthesis and an enhancement of Ca2+ efflux. The inhibition of Ca2+ uptake by PMA was found to decrease as the Ca2+ concentration in the medium was raised from 0.1 to 10.0 microM. This was observed with muscle, but not with platelet vesicles. In contrast, the ability of cyclosporin A to antagonize the inhibition of Ca2+ uptake by PMA also increased when the Ca2+ concentration in the medium was raised from 0.1 to 10.0 microM, but this was observed with both muscle and platelet vesicles. The fact that phospholipase C activity and products from the inositol metabolism have been described as localized in regions of the sarcoplasmic reticulum where Ca2+-ATPase and Ca2+ channels are found suggests a possible physiological role for these products in the regulation of cytosolic Ca2+ levels.
Cardoso
C M
CM
Instituto de Ciências Biomédicas, Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, 21941-590, Rio de Janeiro, Brazil.
Rumjanek
V M
VM
De Meis
L
L
D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology; D002118:Calcium / Q000037:antagonists & inhibitors; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D016572:Cyclosporine / Q000494:pharmacology*; D004075:Diglycerides / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000201:enzymology; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D016559:Tacrolimus / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology*
D004075:Diglycerides; D014475:Uncoupling Agents; D016572:Cyclosporine; C038237:1-oleoyl-2-acetylglycerol; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D016559:Tacrolimus