Pharmacological preconditioning in rabbit myocardium is blocked by chloride channel inhibition.

We have recently proposed that chloride (Cl(-)) channels contribute to ischemic preconditioning (IPC) in the myocardium. To further evaluate this hypothesis, we investigated the role of Cl(-) channels in pharmacological preconditioning. Isolated rabbit cardiomyocytes and isolated buffer-perfused rabbit hearts were initially preconditioned with a 10 min exposure to either an adenosine receptor agonist [2-chloro-N(6)-cyclopentyladenosine (CCPA, 200 nM) and/or N(6)-2-(4-aminophenyl)ethyladenosine (APNEA, 1 microM)] or the PKC activator phorbol 12-myristate 13-acetate (PMA, 1 microM) followed by a 10 or 20 min washout or not preconditioned (control). Cardiomyocytes or whole hearts were then subjected to prolonged ischemic period (45 min simulated ischemia or 40 min of regional myocardial ischemia, respectively) followed by 60 min reperfusion (resuspension in oxygenated medium or release of the transient coronary occlusion, respectively). Indanyloxyacetic acid 94, a selective Cl(-) channel inhibitor that produced substantial inhibition of the regulatory volume decrease (RVD) when given at 10 microM concentration in cultured cardiomyocytes, was administered before ischemia to block RVD through Cl(-) channel inhibition. CCPA, APNEA and PMA significantly (P<0.01) reduced the % of dead cardiomyocytes (by trypan blue staining) after 45 min SI/60 min SR, as compared to controls, while IAA-94 abolished this protection but did not affect PKCepsilon translocation by IPC. We confirmed that IAA-94 blocked IPC-, APNEA- and PMA-induced protection against infarction in the isolated heart model. These findings support our contention that Cl(-) channels are downstream effectors of IPC.