TY - JOUR T1 - Ectonucleotidase in Sympathetic Nerve Endings Modulates ATP and Norepinephrine Exocytosis in Myocardial Ischemia JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 238 LP - 244 DO - 10.1124/jpet.103.049874 VL - 306 IS - 1 AU - Casilde Sesti AU - Motohiro Koyama AU - M. Johan Broekman AU - Aaron J. Marcus AU - Roberto Levi Y1 - 2003/07/01 UR - http://jpet.aspetjournals.org/content/306/1/238.abstract N2 - We recently reported that ATP, coreleased with norepinephrine (NE) from cardiac sympathetic nerves, increases NE exocytosis via a positive feedback mechanism. A neuronal ectonucleotidase (E-NTPDase) metabolizes the released ATP, decreasing NE exocytosis. Excessive NE release in myocardial ischemia exacerbates cardiac dysfunction. Thus, we studied whether the ATP-mediated autocrine amplification of NE release is operative in ischemia and, if so, whether it can be modulated by E-NTPDase and its recombinant equivalent, solCD39. Isolated, guinea pig hearts underwent 10- or 20-min ischemic episodes, wherein NE was released by exocytosis and reversal of the NE transporter, respectively. Furthermore, to restrict the role of E-NTPDase to transmitter ATP, sympathetic nerve endings were isolated (cardiac synaptosomes) and subjected to increasing periods of ischemia. Availability of released ATP at the nerve terminals was either increased via E-NTPDase inhibition or diminished by enhancing ATP hydrolysis with solCD39. P2X receptor blockade with PPADS was used to attenuate the effects of released ATP. We found that, in short-term ischemia (but, as anticipated, not in protracted ischemia, where NE release is carrier-mediated), ATP exocytosis was linearly correlated with that of NE. This indicates that by limiting the availability of ATP at sympathetic terminals, E-NTPDase effectively attenuates NE exocytosis in myocardial ischemia. Our findings suggest a key role for neuronal E-NTPDase in the control of adrenergic function in the ischemic heart. Because excessive NE release is an established cause of dysfunction in ischemic heart disease, solCD39 may offer a novel therapeutic approach to myocardial ischemia and its consequences. The American Society for Pharmacology and Experimental Therapeutics ER -