<正> Objective: To study cross-talk between p-opioid receptor and β-adrenoceptor through determination of the intracellular calcium （ [ Ca2+ ]i ） and cAMP responses in ventricular myocytes of rats subjected to chronic hypoxia for 4 weeks. Methods: Electrically-induced [ Ca2+ ]i transient was measured in single right ventricular myocytes isolated from hearts of chronically hypoxic rats and the age-matched normoxic rats

by using a spectrofluorometric method. Results: β-adrenoceptor stimulation with isoproterenol increased the electrically-induced [ Ca + ]i transient and cAMP in myocytes of normoxic rats. U50

488H

a selective β-opioid receptor agonist

at dose （1 βmol/L） which itself had no effect on the [Ca2 + ]i transient and cAMP

significantly inhibited the effect of isoproterenol. This inhibition was completely abolished in the presence of nor-BNI

a selective K-opioid receptor antagonist. In the ventricular myocytes of chronically hypoxic rats

the inhibition of U50

488H on the increased [ Ca ]i tra