Activation of multiple MAPK pathways (ERKs, JNKs, p38-MAPK) by diverse stimuli in the amphibian heart

We investigated the expression and activation of three MAPK subfamilies in the isolated perfused amphibian heart. ERK was detected as a 43 kDa band; p 38-MAPK was detected as a band corresponding to 38 kDa and JNKs were detect ed as two bands corresponding to 46 and 52 kDa, respectively. PMA induced t he activation of the ERK pathway as assessed by determining the phosphoryla tion state of ERK and the upstream component MEK1/2. PD98059 abolished this activation. p38-MAPK was phosphorylated by sorbitol (almost 12-fold, maxim al within 10-15 min) and JNKs were phosphorylated and activated by sorbitol or anoxia/reoxygenation (approximately 4- and 2.5-fold, respectively). SB2 03580 completely blocked the activation of p38-MAPK by sorbitol. These resu lts indicate that the MAPK pathways activated by phorbol esters, hyperosmot ic stress or anoxia/reoxygenation in the amphibian heart may have an import ant role in this experimental system.