Purinoceptor-mediated vasodilatation in the bovine coronary artery: role of nitric oxide and EDHF Gregor I. Purves, Jill Slavin, Suzanne Wilson, William S. Wilson & William Martin. Institute of Biomedical & Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ.	Print Abstract Search PubMed for: Purves GI Slavin J Wilson S Wilson WS Martin W

Purines exert multiple actions in the cardiovascular system (Boarder & Hourani, 1998). The aim of this study was to determine the roles of nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) and characterise the nature of the purinoceptor involved in the vasodilatation induced by ATP in the bovine coronary artery.

Sections of myocardium containing the left anterior descending coronary artery were cut from bovine hearts at a local abattoir and transported to the laboratory. Coronary arterial rings (2.5 mm wide) were mounted for isometric tension recording on stainless steel hooks in 10 ml organ baths containing Krebs solution at 37°C gassed withO₂/CO₂. In some rings, the endothelium was removed by gentle abrasion. All experiments were conducted in the presence of the cyclooxygenase inhibitor, indomethacin (3 µM). Tone was raised using the thromboxane A₂-mimetic, U46619 (0.01-0.1 µM), and vasodilator responses were elicited to ATP and analogues, added cumulatively (0.01-300 µM). The synthesis of nitric oxide were blocked using N^G-nitro-L-arginine methyl ester (L-NAME, 100 µM) and those of EDHF were blocked using the combination of apamin and charybdotoxin (Ap/ChTx, both 100 nM). Vasodilator responses are given as % reduction (mean ± s.e.mean, n6 observations) of tone and differences were determined using one-way ANOVA with the Bonferroni post-test.

ATP (0.01-300 µM) induced concentration-dependent relaxation of endothelium-containing coronary artery rings (log EC₅₀ -4.63 ± 0.02; max. 93.2 ± 0.7%) and endothelial denudation impaired this relaxation (max. 16.7 ± 1.5%, P<0.001). Maximal relaxation of endothelium-containing rings was reduced to 55.5 ± 1.2% by L-NAME, to 22.8 ± 1.2% by Ap/ChTx and to 7.0 ± 1.3% by all the blockers (P<0.001 for each). Treatment with the non-selective P₂-purinoceptor antagonist, suramin (500 µM, 20 min), had no effect on relaxation to ATP (log EC₅₀ -4.47 ± 0.07; max. 90.1 ± 3.2%). UTP (log EC₅₀ -4.68 ± 0.01; max. 91.1 ± 1.2%) was equipotent with ATP, but a number of other analogues produced much smaller maximal relaxations (ADP 12.0 ± 2.1%; AMP 11.2 ± 1.7%; adenosine 23.8 ± 2.8%; and 2-methylthioATP 0.0 ± 0.0%; P<0.001 for each).

In conclusion, ATP is a powerful endothelium-dependent relaxant of bovine coronary artery, with nitric oxide and EDHF both appearing to contribute to this response. On the basis of the rank order of effectiveness of the analogues tested (ATP=UTP>ADP, AMP, adenosine, 2-methylthioATP) and the lack of effect of suramin, the purinoceptor involved displays the characteristics of the P2Y₂ or the P2Y₄ receptor (Boarder & Hourani, 1998).

Boarder, M.R. & Hourani, S.M.O. (1998) Trends Pharmacol. Sci. 19, 99-107.

Supported by the BHF and Wellcome Trust.