Signaling pathways involved in postconditioning-induced cardioprotection of human myocardium, in vitro

We examined the respective role and relationship between protein kinase C (PKC), mitochondrial adenosine triphosphate-sensitive potassium (mitoKATP) channel and p38 mitogen-activated protein kinase (MAPK) in postconditioning of human myocardium, in vitro. Isometrically contracting, isolated human right atrial trabeculae were exposed to 30 min hypoxia and 60 min reoxygenation. Phorbol 12-myristate 13-acetate (a PKC activator), diazoxide (a mitoKATP opener) and anisomycin (a p38 MAPK activator) were superfused in early reoxygenation alone and with calphostin C (a PKC inhibitor), 5-hydroxy-decanoate (5-HD, a mitoKATP channel inhibitor) and SB 202190 (a p38 MAPK inhibitor). Developed force at the end of the 60 min reoxygenation (FoC60) period was compared between groups (mean ± SD). Phorbol 12-myristate 13-acetate (91 ± 4% of baseline), diazoxide (85 ± 5% of baseline) and anisomycin (90 ± 4% of baseline) enhanced the FoC60 as compared with the control group (53 ± 7% of baseline, P < 0.0001). The enhanced FoC60 induced by phorbol 12-myristate 13-acetate was abolished by calphostin C (52 ± 5% of baseline) and 5-HD (56 ± 3% of baseline), but not by SB 202190 (90 ± 8%). The diazoxide-induced recovery of FoC60 was attenuated by 5-HD (55 ± 6% of baseline), but was not modified by calphostin C (87 ± 5% of baseline) and SB 202190 (90 ± 8% of baseline). The anisomycin-induced recovery of FoC60 was abolished by calphostin C (61 ± 9% of baseline) and SB 202190 (52 ± 8% of baseline), but not by 5-HD (88 ± 6% of baseline). In conclusion, PKC activation, opening of mitoKATP channels and p38 MAPK activation in early reoxygenation induced the postconditioning of human myocardium, in vitro. Furthermore, PKC activation was upstream of the opening of mitoKATP channels; p38 MAPK acted on PKC. Therefore, mitoKATP and p38 MAPK seemed to be involved in two independent pathways.