Role of G proteins and modulation of p38 MAPK activation in the protection by nitric oxide against ischemia-reoxygenation injury

Protein kinase C (PKC)-mediated regulation of the mitogen-activated protein kinases (MAPK) may play a role in the protection afforded by ischemic preconditioning (PC). Nitric oxide (NO) can influence MAPK activation via interaction with PKC or farnesylation of low-molecular-weight (LMWT) G proteins. However, we have recently reported the mechanism of NO-induced cardioprotection to be a PKC-independent process. Therefore, we investigated the role of LMWT G proteins and MAPK signaling in NO-induced cardioprotection against simulated ischemia-reoxygenation (SI-R) injury. Neonatal rat cardiomyocytes treated for 90 min with the NO donor S-nitroso-N-acetyl-L, L-penicillamine (SNAP) 1 mM were protected against 6 h of SI (hypoxic conditions at 37°C with 20 mM lactate, 16 mM KCl at pH 6.2) and 24 h reoxygenation under normal culture conditions. NO-induced protection was blocked by the G protein inhibitor α-hydroxyfarnesylphosphonic acid (αHFP) 10 μM. We studied the time course of p42/44 and p38 MAPK dual-phosphorylation hourly during SI using phosphospecific antibodies, p38 was phosphorylated during SI and the peak phosphorylation was significantly delayed by SNAP pretreatment. The p38 inhibitor SB203580 1 μM, given during SI, protected against injury. Thus the delay in peak p38 activation may contribute to, rather than be the effect of, NO-induced cardioprotection. We have shown that p38β does not contribute to the total p38 signal in our extracts. Thus there is no detectable β isoform. We conclude that the main isoform present in these cells and thought to be responsible for the observed phenomenon, is the α isoform,