Modification of fatty acid composition of the phospholipids of cultured rat ventricular myocytes and the rate of phosphatidylinositol-4,5-bisphosphate hydrolysis.

Cultured neonatal cardiac myocytes have been utilized as a model for the study of the role of fatty acids in the alpha 1-adrenoceptor mediated phosphatidylinositol turnover. Experiments were started 24 h after seeding, when there was a confluent monolayer of beating cardiomyocytes. The cells were incubated for 3-4 days in sera containing culture medium with (1) no additives or (2) a mixture of 107 microM 18:0 and 18:1n-9, or (3) only 214 microM 18:2n-6 or (4) 214 microM 20:5n-3. No differences in the cellular content of the various phospholipid classes among the different groups of fatty acid treated cells were found. The predicted elevations of 18:1n-9, 18:2n-6 and 20:5n-3 associated with a partial depletion of 20:4n-6 were confirmed in all phospholipid classes, except for sphingomyelin. The mol% of 18:0, 18:2n-6, 20:4n-6 and 20:5n-3 in the phosphatidylinositol fraction were respectively 39, 4, 30 and 0.6 for the control treated cells, 34, 3, 15 and 0 for 18:0/18:1n-9 treated cells, 40, 17, 24 and 0.2 for the 18:2n-6 treated cells and 41, 3, 13 and 21 for the 20:5n-3 treated cells. Apart from the observed reductions in the basal rates, the phenylephrine (30 microM) stimulated production of inositolphosphates was reduced by 51% and 71%, respectively in the 18:2n-6 and 20:5n-3 treated cardiomyocytes. The basal rate of inositolphosphate formation was 37% increased in the 18:0/18:1n-9 treated cells. The [3H]-inositol incorporation into phosphatidylinositol 4,5-bisphosphate was only slightly reduced by 18:2n-6 and 20:5n-3 treatments (respectively 12 and 28% compared to control treated cells). Prolonged (30 min) alpha 1-adrenergic stimulation did not affect the contents and fatty acid profiles of any class of phospholipid, not even phosphatidylinositol. In conclusion, variations in the polyunsaturated fatty acid composition of membrane phospholipids do affect the basal and the alpha 1-adrenoceptor stimulated rate of phosphatidylinositol-4,5-bisphosphate hydrolysis. The reducing effects of 18:2n-6 and 20:5n-3 treatment on the rate of inositolphosphate production may be partially ascribed to altered levels of phosphatidyl-inositol 4,5-bisphosphate.