CONCENTRATION-RESPONSE RELATIONSHIPS FOR ADENOSINE AGONISTS DURING PRECONDITIONING OF RABBIT CARDIOMYOCYTES

Although adenosine receptors have been implicated in the induction of preconditioning in a variety of experimental models, there is controve rsy concerning the specific adenosine receptor subtypes mediating this effect. Concentration-protection relationships for adenosine and aden osine agonists in rabbit cardiomyocytes were used to characterize the role of adenosine receptor subtypes in preconditioning. Isolated cells were ischemically preconditioned or pre-incubated for 10 min with inc reasing concentrations of adenosine, CCPA (2-chloro-N-6-cyclopentylade nosine), APNEA (N-6-2-(4-aminophenyl)ethyladenosine), or BNECA (N-6-be nzyl-5'-N'-ethylcarboxamidoadenosine) in the presence or absence of 1 or 10 mu M of the selective A(1)-adenosine antagonist DPCPX (8-Cyclope ntyl-1,3-dipropylxanthine). Following a 30-min post-incubation period, cells were pelleted, layered with oil and ischemically incubated for 180 min. Injury was assessed by osmotic swelling and trypan blue exclu sion of sequential samples, and determination of the areas beneath the mortality curves. Adenosine produced a broad concentration-protection curve which was displaced to the right by DPCPX. The curve for A(1)-s elective agonist CCPA was biphasic, with an initial response below 1 n M and a second above 1 mu M. DPCPX abolished the early response leavin g a steep monophasic curve between 0.1 and 10 mu M CCPA. The APNEA cur ve appeared monophasic, the major slope occurring between 1-100 nM; DP CPX (1 mu M) shifted the concentration-response curve approximate to 3 0-fold and decreased the slope. Adenosine receptor agonist BNECA produ ced preconditioning characterized by a shallow monophasic concentratio n-protection curve with a maximal effect of 49% and an EC(50) of appro ximate to 5 nM; DPCPX shifted the BNECA concentration-protection relat ionship approximate to 40-fold with only a modest increase in slope. A nalysis of the data suggests that induction of preconditioning results from interaction of agonists with the A(1) receptor and a second aden osine receptor having properties consistent with the A(3) receptor. Ad enosine, CCPA, APNEA, BNECA and DPCPX each appear to be selective for the A(1) adenosine receptor subtype in isolated rabbit cardiomyocytes. (C) 1996 Academic Press Limited