Continuous fluorometric assay of Ca2+ transport by liposomes with Quin 2 entrapped: effect of phospholipase A2 and unsaturated long-chain fatty acids.
The amount of free calcium in the cytoplasm is important in stimulation coupled with a number of cellular functions. The putative ionophoretic action of membrane lipid metabolites on Ca2+ offers convenient explanation of the stimulation-coupled mobilization of cytoplasmic Ca2+. To analyze the ionophoretic action of the lipid metabolites, we devised a sensitive method to study Ca2+ transport that uses liposome-entrapped Quin 2. A calcium ionophore, A23187, increased the fluorescence intensity of the Ca2+-Quin 2 complex as a function of Ca2+ transport into liposomes. A similar Ca2+ flux into the liposomes was induced by phospholipase A2 (PLA2) and by various long-chain fatty acids in liposomes that consist of phospholipids containing unsaturated fatty acids. The potencies of the fatty acids for Ca2+ transport is inversely correlated with their melting points. The oxidized products of the unsaturated fatty acids increased the Ca2+ and nonspecific permeability of the biological membranes. These results suggest that stimulation-coupled PLA2 activation might mediates the mobilization of cytoplasmic Ca2+.
D000634:Aminoquinolines; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004910:Erythrocyte Membrane; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005456:Fluorescent Dyes; D006801:Humans; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism*; D008099:Liver; D008970:Molecular Weight; D010740:Phospholipases / Q000494:pharmacology*; D010741:Phospholipases A / Q000494:pharmacology*; D054467:Phospholipases A2; D051381:Rats
D000634:Aminoquinolines; D005231:Fatty Acids, Unsaturated; D005456:Fluorescent Dyes; D008081:Liposomes; D000001:Calcimycin; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; C035739:Quin2; D002118:Calcium