Abstract
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.
Footnotes
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This study was supported by HL 34215 (to C.S., M.K., R.L.), HL 46403 (to A.J.M., M.J.B., R.L.), and HL 47073 and NS 41462 (to A.J.M., M.J.B.) and by a Merit Review grant from the Department of Veterans Affairs (to A.J.M., M.J.B.).
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DOI: 10.1124/jpet.103.049874.
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ABBREVIATIONS: NE, norepinephrine; P2XR, purinergic P2X receptor; E-NTPDase, ectonucleoside triphosphate diphosphohydrolase; HBS, HEPES-buffered saline; DMI, desipramine; solCD39, recombinant soluble form of human E-NTPDase1/CD39; ARL67156, 6-N,N-diethyl-β-γ-dibromomethylene-d-adenosine-5′-triphosphate; PPADS, pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid; TLC, thin-layer chromatography; ANOVA, analysis of variance.
- Received January 31, 2003.
- Accepted April 3, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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