Eicosapentaenoic Acid Incorporation in Membrane Phospholipids Modulates Receptor-mediated Phospholipase C and Membrane Fluidity in Rat Ventricular Myocytes in Culture

• Published in: Journal of molecular and cellular cardiology 1996-05, Vol.28 (5), p.1097-1108
• Main Authors: de Jonge, Henriëtte W., Dekkers, Dick H.W., Bastiaanse, Lars E.M., Bezstarosti, Karel, van der Laarse, Arnoud, Lamers, Jos M.J.
• Format: Article
• Language: English
• Subjects: Adrenergic alpha-Agonists - pharmacology; Animals; Cell culture; Cell Membrane - metabolism; Cells, Cultured; Contractile activity; Eicosapentaenoic Acid - chemistry; Eicosapentaenoic Acid - metabolism; Electrical activity; Endothelin-1 - pharmacology; Heart Ventricles - ultrastructure; Inositol phosphate production; Membrane cholesterol; Membrane fluidity; Membrane Fluidity - drug effects; Membrane phospholipids; Myocardial Contraction - drug effects; Phenylephrine - pharmacology; Phosphatidylinositol cycles; Phospholipids - chemistry; Phospholipids - metabolism; Polyunsaturated fatty acids; Rat ventricular myocytes; Rats; Rats, Wistar; Receptors, Adrenergic, alpha - physiology; Saponin permeabilization; Signal Transduction - drug effects; Type C Phospholipases - physiology; Ventricular Function
• ISSN: 0022-2828; 1095-8584
• DOI: 10.1006/jmcc.1996.0101

The influence of increased incorporation of linoleic acid (18:2n-6) and eicosapentaenoic acid (20:5n-3) in membrane phospholipids on receptor-mediated phospholipase C β(PLC- β) activity in cultured rat ventricular myocytes was investigated. For this purpose, cells were grown for 4 days in control, stearic acid (18:0)/oleic acid (18:1n-9), 18:2n-6 and 20:5n-3 enriched media, and subsequently assayed for the basal- and phenylephrine- or endothelin-1-induced total inositol phosphate formation. The various fatty acid treatments resulted in the expected alterations of fatty acid composition of membrane phospholipids. In 18:2n-6-treated cells, the incorporation of this 18:2n-6 in the phospholipids increased from 17.1 mol % in control cells to 38.9 mol %. In 20:5n-3-treated cells, incorporation of 20:5n-3 and docosapentaenoic acid (22:5n-3) in the phospholipids increased from 0.5 and 2.7 mol % in control cells to 23.2 and 9.7 mol %, respectively. When 20:5n-3-treated cells were stimulated with phenylephrine or endothelin-1, the inositolphosphate production decreased by 33.2% and increased by 43.4%, respectively, as compared to cells grown in control medium. No effects were seen in 18:2n-6-treated cells. When 18:0/18:1n-9-treated cells were stimulated with endothelin-1, inositolphosphate formation increased by 26.4%, whereas phenylephrine-stimulated inositolphosphate formation was not affected. In saponin-permeabilized cells, that were pre-treated with 20:5n-3, the formation of total inositolphosphates after stimulation with GTP γS, in the presence of Ca 2+, was inhibited 19.3%. This suggests that the 20:5n-3 effect on intact cardiomyocytes could be exerted either on the level of agonist–receptor, receptor–GTP-binding-protein coupling or GTP-binding-protein–PLC- βinteraction. Investigation of the time course of saponin-induced permeabilization of the cardiomyocytes, measured by the release of lactate dehydrogenase, unmasked a slight decrease in the rate of permeabilization by 20:5n-3 pretreatment, indicating a protective effect. This led the authors to measure the cholesterol/phospholipid molar ratio, the double bond index of membrane phospholipids, and the membrane fluidity; the latter by using a diphenylhexatriene probe. In 20:5n-3-pretreated cells, a strong increase in the cholesterol/phospholipid molar ratio (from 0.23 to 0.39), a marked increase in the double bond index (from 1.76 to 2.33), and a slight decrease in fluidity (steady-state anisotropy r ssof the