Differential turnover of polyunsaturated fatty acids in plasmalogen and diacyl glycerophospholipids of isolated cardiac myocytes

To investigate the relative turnover of esterified polyunsaturated fatty acids in diacylglycerophospholipids and plasmalogens in isolated cardiac myocytes, we characterized the phospholipid composition and distribution of radiolabel in different phospholipid classes and in individual molecular species of diradyl choline (CGP) and ethanolamine (EGP) glycerophospholipids after incubation of isolated cardiac myocytes with 3H]arachidonate or 14C]linoleate. Plasmalogens in CGP (55%) and EGP (42%) quantitatively accounted for the total plasmalogen content (39%) of cardiac myocyte phospholipids. Plasmalogens comprised 86% and 51% of total arachidonylated CGP and EGP mass, respectively, and 3H]arachidonate was primarily incorporated into plasmalogens in both CGP (65%) and EGP (61%) classes. The specificity activity of 3H]arachidonylated diacyl-CGP was approximately 2- to 5-fold greater than that of 3H]arachidonylated choline plasmalogen, whereas comparable specific activities were found in the 3H]arachidonate-labeled ethanolamine plasmalogen and diacyl-EGP pools. Of the total linoleate-containing CGP and EGP mass, 54% and 57%, respectively, was esterified to plasmalogen molecular species. However, 14C]linoleate was almost exclusively incorporated into diacyl-CGP (96%) and diacyl-EGP (86%). The specific activities of 14C]linoleate-labeled diacyl-CGP and diacyl-EGP were 5- to 20-fold greater than that of the 14C]linoleate-labeled plasmalogen pools. The differential incorporation of polyunsaturated fatty acids in plasmalogens and diacylglycerophospholipids demonstrates that the metabolism of the sn-2 fatty acyl moiety in these phospholipid subclasses is differentially regulated, possibly fulfilling separate and distinct physiologic roles.