ENHANCED PHOSPHOLIPASE A(2) ACTIVITY IN CULTURED CARDIOMYOCYTES FROM NEWBORN SPONTANEOUSLY HYPERTENSIVE RAT

1. Changes in membrane lipid composition and metabolism could particip ate in myocardial membrane dysfunction in essential or experimental hy pertension, Phospholipid-bound fatty acid profile and metabolism are a ltered in cultured heart myocytes of newborn genetically hypertensive rats, The present study was designed to investigate the participation of phospholipase A(2) in these modifications, 2. Phospholipase A(2) ac tivity of cultured cardiomyocytes of neonate spontaneously hypertensiv e rats and normotensive control Wistar-Kyoto rats was compared, The en zyme activity was measured using 2-[1-C-14]arachidonyl-phosphatidyleth anolamine as substrate, In both strains, Ca2+-dependent and independen t phospholipase A(2) activities were present, Only the Ca2+-dependent enzyme activity was altered in spontaneously hypertensive rat cardiomy ocytes, With 0.2 mmol/l substrate and 5 mmol/l Ca2+, the phospholipase A(2) activities were 79.0 +/- 13.4 and 26.0 +/- 3.6 nmol h(-1) mg(-1) of protein in spontaneously hypertensive and Wistar-Kyoto rat cardiom yocytes respectively (n=10 in both cases, P=0.001). The maximum veloci ty of the enzyme was three times higher in spontaneously hypertensive rat than in Wistar-Kyoto rat, without changes in the apparent affinity of the enzyme for its substrate, 3. The present results demonstrate a n enhanced phospholipase A(2) activity in cultured heart muscle cells of spontaneously hypertensive rats, which could be genetically determi ned.