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1 The effects of pharmacological preconditioning with U50488H (U[sub 50]), a selective κ-opioid receptor agonist, on Ca[sup 2+] homeostasis in rat ventricular myocytes subjected for 9 min to metabolic inhibition (MI) and anoxia (A), consequences of ischaemia, were studied and compared with those of preconditioning with brief periods of MI/A. 2 Precondition with 30 µM of U[sub 50] for three cycles of 1 min each cycle separated by 3 min of recovery (UP) significantly increased the percentage of non-blue cells following MI/A. The effect of UP is the same as that of preconditioning with an inhibitor of glycolysis and an oxygen scavenger for three 1-min cycles separated by three-minute recovery (MI/AP). The results indicate that like MI/AP, UP also confers cardioprotection. 3 MI/A increased intracellular Ca[sup 2+] ([Ca[sup 2+]][sub i]) and reduced the amplitude of caffeine-induced [Ca[sup 2+]][sub i] transients, an indication of Ca[sup 2+] content in the sarcoplasmic reticulum (SR). MI/A also reduced the electrically-induced [Ca[sup 2+]][sub i] transient, that indicates Ca[sup 2+]-release during excitation-contraction coupling, and Ca[sup 2+] sparks in unstimulated myocytes, that indicates spontaneous Ca[sup 2+]-release from SR. It also prolonged the decline of the electrically-induced [Ca[sup 2+]][sub i] transient and slowed down the recovery of the electrically-induced [Ca[sup 2+]][sub i] transient after administration of caffeine. In addition, MI/A prolonged the decline of caffeine induced [Ca[sup 2+]]i transient, an indication of Na[sup +]-Ca[sup 2+] exchange activity, and UP prevented it. So UP, that confers cardioprotection, prevented the changes induced by MI/A. With the exception of Ca[sup 2+]-spark, which was not studied, the effects of MI/AP are the same as those of UP. 4 It is concluded that pharmacological preconditioning with U[sub 50], that confers immediate cardioprotection, prevents changes of Ca[sup 2+] homeostasis altered by MI/A in... [ABSTRACT FROM AUTHOR]