Differential activation of extracellular signal regulated kinase isoforms in preconditioning and opioid-induced cardioprotection

Stimulation of the delta (1)-opioid receptor has been shown to trigger isch emic preconditioning (IPC). Additionally, myocardial ischemia/reperfusion i nduces the activation of extracellular signal-regulated kinase (ERK). There fore, we examined the role of ERK in acute cardioprotection induced by delt a (1)-opioid receptor stimulation or IPC. Infarct size (IS) was expressed a s a percentage of the area at risk (AAR). Control animals had an IS/AAR of 60.6 +/- 1.8. IPC and delta (1)-opioid receptor stimulation with TAN-67 red uced IS/AAR (8.2 +/- 1.3 and 30.2 +/- 2.4). Inhibition of ERK with the sele ctive MEK-1 antagonist, PD 098059 during IPC or TAN-67 administration signi ficantly reduced cardioprotection (41.5 +/- 6.4 and 63.0 +/- 4.8). Western Blot analysis and subsequent densitometry corroborated these observations. Control, TAN-67-, or IPC-treated hearts were harvested after 0, 5, 15, and 30 min of ischemia or 5, 30, and 60 min of reperfusion and separated into c ytosolic and nuclear fractions. Both isoforms of ERK (p44 and p42) rapidly increased to greater levels throughout reperfusion in the nuclear fraction of IPC- and opioid-treated versus control rats, however, this increase was not attenuated by PD 098059. Conversely, the rapid activation of the 44-kDa isoform of ERK after 5 min of reperfusion in the cytosolic fraction was si gnificantly increased in IPC- and opioid-treated hearts versus control, and this increase was abolished by pretreatment with PD 098059. Additionally, p42 was activated in the cytosolic fraction of IPC-treated animals. These r esults suggest a key role for the 44-kDa isoform of ERK in the cytoplasm du ring cardioprotection induced by either IPC or stimulation of the delta (1) -opioid receptor.