INHIBITION OF STORE-DEPENDENT CAPACITATIVE CA2-ACIDS( INFLUX BY UNSATURATED FATTY)

The effects of the unsaturated fatty acids, arachidonic and oleic acid , on the influx of Ca2+ activated by depletion of intracellular stores with thapsigargin were investigated in various cell types. By using a Ca(2+)free/Ca2+ reintroduction protocol, we observed that arachidonic acid (2 to 5 mu M) inhibited thapsigargin-induced rises in cytosolic free Ca2+ ([Ca2+](i)) in Ehrlich tumor cells, Jurkat T lymphocytes, ra t thymocytes, and Friend erythroleukemia and PC12 rat pheochromocytoma cells. This effect was attributed to the inhibition of Ca2+ entry, si nce arachidonate also inhibited thapsigargin-stimulated unidirectional entry of the Ca2+ surrogates Ba2+ and Mn2+. In Ehrlich cells, the IC, , for arachidonic and oleic acid was 1.2 and 1.8 mu M, respectively. T he inhibition appeared to depend on the ratio [fatty acid]/[cells] rat her than on the absolute fatty acid concentration. Experiments with [H -3]-oleic acid revealed that the inhibitory activity was not correlate d with cell internalisation and metabolism of the fatty acid. The inhi bition was reverted by removal of the fatty acid bound to cell membran e by fatty acid-free albumin treatment. The unsaturated fatty acids ha d no effect on ATP/ADP cell levels and plasma membrane potential. Phar macological evidence indicated that cell phosphorylation/dephosphoryla tion events, and pertussis toxin-sensitive G proteins were not involve d. Other amphipathic lipophilic compounds, i.e. 2-bromopalmitic acid, retinoic acid, sphingosine, and dihydrosphingosine, mimicked arachidon ic/oleic acid as they inhibited thapsigargin-stimulated Ca2+ influx in an albumin-reversible fashion. These results suggest that physiologic ally relevant (unsaturated) fatty acids can inhibit capacitative Ca2influx possibly because they intercalate into the plasma membrane and directly aff ect the activity of the channels involved.