Continuous fluorometric assay of Ca2+ transport by liposomes with Quin 2 entrapped: Effect of phospholipase A2 and unsaturated long-chain fatty acids.

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The amount of free calcium in the cytoplasm is important in stimulation coupled with a number of cellular functions. The putative iono-phoretic 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 cal-cium 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 nons-pecific permeability of the biological membranes. These results suggest that stimulation-coupled PLA2 activation might mediates the mobilization of cytoplasmic Ca2+.
日本細胞生物学会の論文