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RECEPTORS AND SIGNAL TRANSDUCTION

Activation of MAPKs in thrombin-stimulated ventricular myocytes is dependent on Ca²⁺-independent PLA₂

Department of Pathology, St. Louis University School of Medicine, St. Louis, Missouri

Submitted 27 September 2005 ; accepted in final form 1 December 2005

Thrombin stimulation of isolated rabbit ventricular myocytes activates a membrane-associated, Ca²⁺-independent PLA₂ (iPLA₂) that selectively hydrolyzes plasmalogen phospholipids and results in increased production of arachidonic acid and lysoplasmenylcholine. To determine whether MAPK regulates myocardial iPLA₂ activity, we isolated ventricular myocytes from rabbit heart by collagenase digestion and pretreated them with MAPK inhibitors before stimulating them with thrombin. Pretreatment with PD-98059 to inhibit p42/44 MAPK or SB-203580 to inhibit p38 MAPK had no significant effect on thrombin-stimulated, membrane-associated iPLA₂ activity. Thrombin stimulation resulted in significant increases in both p42/44 and p38 MAPK activity after 2 min. Pretreatment with the iPLA₂-selective inhibitor bromoenol lactone completely inhibited thrombin-stimulated MAPK activity, suggesting that activation of MAPKs was dependent on iPLA₂ activation. Ventricular myocyte MAPK activity was increased by incubation of the myocytes with lysoplasmenylcholine, a metabolite produced by iPLA₂-catalyzed membrane plasmalogen phospholipid hydrolysis. Altogether, these data suggest that activation of MAPKs occurs downstream of and is dependent on iPLA₂ activation in thrombin-stimulated rabbit ventricular myocytes.

lysoplasmenylcholine; cell signaling; protease-activated receptors

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