STIMULATION OF DIFFERENT PHOSPHOLIPASE A(2) ISOFORMS BY TNF-ALPHA ANDIL-1-BETA IN ADULT-RAT VENTRICULAR MYOCYTES

We previously showed that in adult rat ventricular myocytes interleuki n (IL)-1 beta activates a membrane-associated, Ca2+-independent phosph olipase A(2) (iPLA(2)). In this study, we examined the possible existe nce of different PLA(2) isoforms and effects of tumor necrosis factor (TNF)-alpha on iPLA(2) activities. Western blot analysis identified iP LA(2) in both membrane (similar to 82 kDa) and cytosolic (similar to 4 0 kDa) fractions and identified Ca2+-dependent PLA(2) (cPLA(2)) only i n cytosolic fractions. With plasmenylcholine or alkylacyl glycerophosp horylcholine as substrate, TNF-alpha elicited a twofold transient incr ease in cytosolic iPLA(2) activity accompanied by an increase in arach idonic acid release and decreased membrane-associated iPLA(2) activity with plasmenylcholine. With phosphatidylcholine as substrate, TNF-alp ha decreased both cytosolic and membrane-associated iPLA(2) activities . TNF-alpha-induced increases in cytosolic iPLA(2) activity and arachi donic acid release were completely blocked by methyl arachidonyl fluor ophosphonate (MAFP) but not by bromoenol lactone (BEL). TNF-alpha and IL-1 beta together enhanced synergistically cytosolic and membrane PLA (2) activities and arachidonic acid release that were blocked differen tially by MAFP and EEL, respectively, and inhibited completely by MAFP plus EEL. These results suggest that TNF-alpha and IL-1 beta act on d ifferent PLA(2) isoforms in ventricular myocytes.