Adenosine-mediated early preconditioning in mouse: protective signaling and concentration dependent effects.

Objectives: Signaling in adenosine-mediated preconditioning is controversial. We examined roles of mitochondrial (mito) K(ATP) channels, protein kinase C (PKC) and nitric oxide (NO).

Methods: Langendorff perfused C57/Bl6 mouse hearts were subjected to 20 min ischemia and 45 min reperfusion. Effects of adenosine-mediated preconditioning were assessed in the absence and presence of signaling inhibitors.

Results: Control hearts recovered 70+/-2 mmHg ventricular pressure, and released 18.1+/-2.0 IU/g lactate dehydrogenase (LDH). Preconditioning with 10 microM adenosine limited necrosis (10.6+/-1.4 IU/g) without modifying contractility (72+/-2 mmHg) whereas 50 microM adenosine reduced necrosis (10.3+/-1.6 IU/g) and contractile dysfunction (91+/-2 mmHg). All protective effects of 10 and 50 microM adenosine were abrogated by mito K(ATP) channel blockade with 100 microM 5-hydroxydecanoate (5-HD) during the 'trigger' phase, but unaltered by PKC or NO synthase inhibition with 3 microM chelerythrine or 100 microM N(G)-nitro-L-arginine methyl ester (L-NAME), respectively. Protection against necrosis was eliminated by 5-HD but unaltered by chelerythrine or L-NAME during the 'mediation' phase (ischemia-reperfusion). Reduced contractile dysfunction with 50 microM adenosine was partially sensitive to 5-HD and chelerythrine, and only eliminated by co-infusion of the inhibitors.

Conclusions: Adenosine-mediated preconditioning is dose-dependent with high level stimulation reducing contractile dysfunction in addition to necrosis. Preconditioning is triggered by a mito K(ATP) channel dependent process independently of PKC and NO. Subsequent protection against necrosis is also mediated by a mito K(ATP) channel dependent process independent of PKC and NO. In contrast, functional protection may be mediated by parallel mito K(ATP) and PKC dependent paths.