Cardioprotection of preconditioning by metabolic inhibition in the rat ventricular myocyte -: Involvement of κ-opioid receptor

act--To determine whether opjoid receptors (ORs) are involved in the delayed cardioprotection of ischemic preconditioning (TP), 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 5 x 10(-6) mol/L nor-binaltorphimine (nor-BNI), a selective kappa-OR antagonist, but not 5X10(-6) mol/L CTOP, a selective mu-OR antagonist, or 5x10(-6) mol/L naltrindole,a selective delta-OR antagonist, the cardioprotection of MIP was significantly attenuated. To verify the role of kappa-OR, we studied the effects of severe MI after pretreatment with the kappa-OR agonist U50,488H;;(UP) for 30;minutes. U50,488Hat 3x10(-6) to 1x10(-4) mol/L increased cell visibility concentration dependently with an EC,of 3.311X10(-6) mol/L. In the presence of 5x10(-6) nor-BNI, the cardioprotection of UP (3x10(-5) mol/L) was blocked. A time course study showed that UP-induced cardioprotection occurred in 2 windows: the first occurred similar to 1 hour later and the other occurred 16 to 20 hours later. Additional studies on cell contraction and intracellular Ca2+ ([Ca2+](i)) revealed that both UP and MIP attenuated the inhibitory effects of Severe MI on contractility and electrically induced [Ca2+], 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 [Ca2+](i).