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.