EctoNucleotidase in cardiac sympathetic nerve endings modulates ATP-mediated feedback of norepinephrine release.
ATP, coreleased with norepinephrine, affects adrenergic transmission by acting on purinoceptors at sympathetic nerve endings. Ectonucleotidases terminate the actions of ATP. Previously, we had preliminary evidence for ectonucleotidase activity in cardiac sympathetic nerve terminals. Therefore, we investigated whether this ectonucleotidase might influence norepinephrine release in the heart. Sympathetic nerve endings isolated from guinea pig heart (cardiac synaptosomes) were rich in Ca(2+)-dependent ectonucleotidase activity, as measured by metabolism of exogenously added radiolabeled ATP or ADP. By its inhibitor profile, ectonucleotidase resembled ectonucleoside triphosphate diphosphohydrolase 1 (E-NTPDase1). Exogenous ATP elicited concentration-dependent norepinephrine release from cardiac synaptosomes (EC(50) 0.96 microM). This release was antagonized by the P2X receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) (10 microM) and potentiated by the P2Y receptor antagonist 2'-deoxy-N(6)-methyladenosine-3',5'-diphosphate (MRS 2179) (30 nM). Norepinephrine release promoted by ATP was also potentiated by the nucleotidase inhibitor 6-N,N-diethyl-beta-gamma-dibromomethylene-D-adenosine-5'-triphosphate (ARL67156) (30 microM) and blocked by a recombinant, soluble form of human E-NTPDase1 (solCD39). In contrast, ARL67156 had no effect on norepinephrine release induced by the nonhydrolyzable analog, alpha, beta-methyleneadenosine-5'-triphosphate (alpha,beta-MeATP). Depolarization of cardiac synaptosomes with K(+) elicited release of endogenous norepinephrine. This was attenuated by PPADS and solCD39 and potentiated by MRS 2179 and ARL67156. Importantly, our results demonstrate that facilitation of ATP-induced norepinephrine release from cardiac sympathetic nerves is a composite of two autocrine components: positive, mediated by P2X receptors, and negative, mediated by P2Y receptors. Modulation of norepinephrine release by coreleased ATP is terminated by endogenous as well as exogenous ectonucleotidase. We propose that ectonucleotidase control of norepinephrine release should provide cardiac protection in hyperadrenergic states such as myocardial ischemia.
Sesti
Casilde
C
Department of Pharmacology, Weill Medical College of Cornell University, New York, New York 10021, USA.
Broekman
M Johan
MJ
Drosopoulos
Joan H F
JH
Islam
Naziba
N
Marcus
Aaron J
AJ
Levi
Roberto
R
D015720:5'-Nucleotidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D002855:Chromatography, Thin Layer; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005246:Feedback; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000294:innervation*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009411:Nerve Endings / Q000187:drug effects / Q000201:enzymology*; D009638:Norepinephrine / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000201:enzymology*; D013574:Synaptosomes / Q000187:drug effects / Q000201:enzymology
C092431:6-N,N-diethyl-beta,gamma-dibromomethylene-D-ATP; D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D015720:5'-Nucleotidase; D002118:Calcium; D009638:Norepinephrine