Evidence of transcriptional and translational components in anti-ischemic effects of adenosine

Adenosine protects against myocardial ischemic injury via poorly defined mechanisms. We examined effects of inhibition of gene transcription, mRNA translation, and mitochondrial K_ATP channels on cardioprotective effects of adenosine in mouse hearts subjected to 20-min ischemia. Adenosine treatment reduced postischemic lactate dehydrogenase efflux (indicating necrosis) from 24 ± 2 to 9 ± 1 IU/g, and postischemic diastolic contracture from 21 ± 2 to 5 ± 2 mm Hg, and enhanced postischemic ventricular pressure development from 72 ± 3 to 135 ± 4 mm Hg. The antinecrotic response was reduced ≈50% by inhibition of protein translation (10 μM cycloheximide, CHX), unaltered by inhibition of transcription (20 μM actinomycin D, Act-D), and abrogated by mitochondrial K_ATP channel inhibition (100 μM 5-hydroxydecanoate, 5-HD). In contrast, protection against contractile dysfunction was reduced but not eliminated by CHX, Act-D, and 5-HD, and inhibitory effects CHX and Act-D were not additive with those of 5-HD, supporting a common mechanistic path. Inhibitory effects of Act-D were mimicked by 1.5 μM α-amanitin. These data provide evidence that adenosine limits necrosis in a mito K_ATP channel-dependent manner involving protein translation. The translational component is not dependent upon mRNA transcription. Adenosine also substantially reduces contractile dysfunction via a pathway involving mitochondrial K_ATP channel activation, protein translation, and mRNA transcription. Protection independent of this path was also evident. Thus, distinct signaling pathways appear to be involved in adenosine-mediated protection against postischemic necrosis and contractile dysfunction.