Direct preconditioning of cardiac ventricular myocytes via adenosine A1 receptor and KATP channel.

Both adenosine receptor and ATP-sensitive K (KATP) channel mediate the protective effect of ischemic preconditioning in the intact heart. The objective of the present study was to determine the role of adenosine receptor and KATP channel as well as their interaction in simulating and mediating preconditioning of the cardiac myocyte. Cardiac ventricular myocytes cultured from chick embryos 14 days in ovo were developed as a myocyte model of preconditioning. Myocytes were preconditioned by exposing them to 5-min hypoxia, termed preconditioning hypoxia, before a second 90-min hypoxia. Preconditioning resulted in a 64 +/- 3% decrease in the amount of creatine kinase released and a 66 +/- 2% reduction in the percentage of myocytes (+/-SE, n = 11) killed. Glibenclamide or 5-hydroxydecanoic acid (5-HD), when present during the preconditioning hypoxia, blocked the preconditioning effect. Prior exposure of the myocytes to pinacidil also led to a decrease in the injury sustained during the 90-min hypoxia. The protective effect of pinacidil was blocked by glibenclamide or 5-HD, suggesting that KATP channel activation can mimic as well as mediate preconditioning. Adenosine receptor antagonist 8-sulfophenyltheophylline (8-SPT) blocked the protective effect of preconditioning hypoxia. Adenosine or the A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) can replace preconditioning hypoxia and mimic preconditioning; this effect was fully antagonized by 8-SPT, glibenclamide, or 5-HD. Adenosine A1-receptor activation caused a glibenclamide-sensitive inhibition of the basal 45Ca influx and basal myocyte contractile amplitude, consistent with coupling of A1 receptor to stimulation of KATP channel in the myocytes. The data provide direct evidence that myocyte KATP channel is the effector downstream from adenosine A1 receptor in mediating the direct preconditioning of cardiac myocytes.