Alterations in polyunsaturated fatty acid composition of cardiac membrane phospholipids and α1 adrenoceptor mediated phosphatidylinositol turnover

Study objective - The aim of the study was to investigate the steps at which polyunsaturated fatty acids are involved in α1 adrenoceptor mediated phosphatidylinositol turnover. Design - Phosphatidylinositol turnover rates were investigated after preincubating neonatal rat ventricular myocytes with culture media enriched with linoleic acid (18:2n-6) or eicosapentaenoic acid (20:5n-3) to change the polyunsaturated fatty acid composition of their membrane phospholipids. Experimental material - Cardiomyocytes were isolated from ventricles of 2-4 d old Wistar rats by trypsinization and were then cultured. Experiments were started 48 h after seeding, when there was a confluent monolayer of beating cardiomyocytes. Measurements and results - In 18:2n-6 treated cells the 18:2n-6 content in the total phospholipid fraction rose from 45 to 68 nmol·mg-1 protein; in 20:5n-6 treated cells the 20:5n-3 content rose from 1.5 to 12.5 nmol·mg-1 protein, and the docosapentaenoic acid (22:5n-3) content rose from 5.1 to 14.7 nmol·mg-1protein. The major n-3 fatty acid, 22:6n-3 (11.4 nmol·mg-1 protein), did not change after 20:5n-3 treatment. Although the phosphatidylinositol fraction showed changes paralleling those in the total phospholipids, none were significant. In this fraction the major n-3 fatty acid appeared to be 22:5n-3 (0.4 nmol·mg-1 protein). The fatty acid treated cells were prelabelled with [3H]-inositol to estimate the rate of phosphatidylinositol-4,5-bisphosphate turnover. There were no differences in the rate of [3H]-inositolphosphate formation between control, 18:2n-6 treated cells, and 20:5n-3 treated cells. Prolonged α1 adrenergic stimulation of control and treated cells did not change the polyunsaturated fatty acid composition of the total phospholipid and phosphatidylinositol fractions. Conclusions - The α1 adrenoceptor mediated phosphatidylinositol turnover rate is not affected by changes in polyunsaturated fatty acid composition of membrane phospholipids, neither does prolonged α1 adrenergic stimulation lead to significant depletion of any specific or total polyunsaturated fatty acids in the phosphatidylinositol lipids