Cardioprotection of Preconditioning by Metabolic Inhibition in the Rat Ventricular Myocyte Involvement of k-Opioid Receptor

To determine whether opioid receptors (ORs) are involved in the delayed cardioprotection of ischemic preconditioning (IP), the effect of severe metabolic inhibition (MI) with a glucose-free buffer that contained sodium cyanide and 2-deoxy-D-glucose on the viability of isolated rat ventricular myocytes was first determined 20 hours after preconditioning with a sublethal metabolic inhibition (MIP) with a glucose-free buffer that contained 2-deoxy-D-glucose and lactate for 30 minutes in the presence of OR antagonists. With the use of trypan blue exclusion as an index of cell viability, severe MI killed .60% of the cells and the value increased significantly after MIP. In the presence of 5310 mol/L nor-binaltorphimine (nor-BNI), a selective k-OR antagonist, but not 5310 mol/L CTOP, a selective m-OR antagonist, or 5310 mol/L naltrindole, a selective d-OR antagonist, the cardioprotection of MIP was significantly attenuated. To verify the role of k-OR, we studied the effects of severe MI after pretreatment with the k-OR agonist U50,488H (UP) for 30 minutes. U50,488H at 3310 to 1310 mol/L increased cell viability concentrationdependently with an EC50 of 3.311310 26 mol/L. In the presence of 5310 nor-BNI, the cardioprotection of UP (3310 mol/L) was blocked. A time course study showed that UP-induced cardioprotection occurred in 2 windows: the first occurred '1 hour later and the other occurred 16 to 20 hours later. Additional studies on cell contraction and intracellular Ca ([Ca]i) revealed that both UP and MIP attenuated the inhibitory effects of severe MI on contractility and electrically induced [Ca]i transient in single ventricular myocytes. On blockade of protein kinase C, the delayed cardioprotections of UP and MIP were significantly attenuated. In conclusion, the results of the present study have provided evidence that k-OR mediates the cardioprotection of MIP, which may involve protein kinase C and [Ca]i. (Circ Res. 1999;84:1388-1395.)