ACTIVATION OF PROTEIN-KINASE-C INCREASES ADENOSINE PRODUCTION IN THE HYPOXIC CANINE CORONARY-ARTERY THROUGH THE EXTRACELLULAR PATHWAY

Both ischemia and hypoxia increase adenosine production in the heart. This study tested whether hypoxia increases adenosine production in the coronary artery via ecto-5'-nucleotidase and the role of protein kinase C in this condition. Canine left circumflex coronary artery was rapidly removed and incubated in 10 mL Krebs-Henseleit solution for 30 minutes. The Krebs-Henseleit solution contained 5'-iodotubercidin and 2'-deoxycoformycin, which inhibit adenosine kinase and adenosine deaminase, respectively. Adenosine production was measured in intact coronary arteries under normoxic conditions (16.2+/-1.2 pmol/mg protein), Adenosine production was reduced by 27% after removal of endothelium. Ecto-5'-nucleotidase activity of coronary arteries with and without endothelium was 51+/-6 and 41+/-4 nmol/mg protein per minute under normoxic conditions. Hypoxia increased adenosine production to 27.0+/-2.3 and 20.0+/-0.8 pmolimg protein with and without endothelium, Hypoxia also increased ecto-5'-nucleotidase activity of coronary arteries with and without endothelium (74+/-8 and 53+/-5 nmol/mg protein per minute; P<.05). Increases in adenosine production under hypoxic conditions were blunted by both an inhibitor of ecto-5'-nucleotidase and inhibitors of protein kinase C, Activation of ecto-5'-nucleotidase was blunted by an inhibitor of protein kinase C. These results indicate that hypoxia increased extracellular adenosine production and activated ecto-5'-nucleotidase via activation of protein kinase C in coronary arterial smooth muscle and endothelial cells. Increased adenosine production in coronary arteries during hypoxia may contribute to coronary vasodilation and cardioprotection against ischemic injury.