Author(s): Flood A, Headrick JP
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Abstract Coronary responses to adenosine agonists were assessed in perfused mouse and rat hearts. The roles of nitric oxide (NO) and ATP-dependent K(+) channels (K(ATP)) were studied in the mouse. Resting coronary resistance was lower in mouse vs rat, as was minimal resistance (2.2+/-0.1 vs 3.8+/-0.2 mmHg ml(-1) min(-1) g(-1)). Peak hyperaemic flow after 20 - 60 s occlusion was greater in mouse. Adenosine agonists induced coronary dilation in mouse, with pEC(50)s of 9.4+/-0.1 for 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethyl carboxamidoadenosine (CGS21680, A(2A)-selective agonist), 9.3+/-0.1 for 5'-N-ethylcarboxamidoadenosine (NECA, A(1)/A(2) agonist), 8.4+/-0.1 for 2-chloroadenosine (A(1)/A(2) agonist), 7.7+/-0.1 for N(6)-(R)-(phenylisopropyl)adenosine (R-PIA, A(1)/A(2B) selective), and 6.8+/-0.2 for adenosine. The potency order (CGS21680=NECA>2-chloroadenosine>R-PIA>adenosine) supports A(2A) adenosine receptor-mediated dilation in mouse coronary vessels. 0.2 - 2 microM of the A(2B)-selective antagonist alloxazine failed to alter CGS21680 or 2-chloroadenosine responses. pEC(50)s in rat were 6.7+/-0.2 for CGS21680, 7.3+/-0.1 for NECA, 7.6+/-0.1 for 2-chloroadenosine, 7.2+/-0.1 for R-PIA, and 6.2+/-0.1 for adenosine (2-chloroadenosine>NECA=R-PIA>CGS21680> adenosine), supporting an A(2B) adenosine receptor response. NO-synthase antagonism with 50 microM N(G)-nitro L-arginine (L-NOARG) increased resistance by approximately 25\%, and inhibited responses to CGS21680 (pEC(50)=9.0+/-0.1), 2-chloroadenosine (pEC(50)=7.3+/-0.2) and endothelial-dependent ADP, but not sodium nitroprusside (SNP). K(ATP) channel blockade with 5 microM glibenclamide increased resistance by approximately 80\% and inhibited responses to CGS21680 in control (pEC(50)=8.3+/-0.1) and L-NOARG-treated hearts (pEC(50)=7.3+/-0.1), and to 2-chloroadenosine in control (pEC(50)=6.7+/-0.1) and L-NOARG-treated hearts (pEC(50)=5.9+/-0.2). In summary, mouse coronary vessels are more sensitive to adenosine than rat vessels. A(2A) adenosine receptors mediate dilation in mouse coronary vessels vs A(2B) receptors in rat. Responses in the mouse involve a sensitive NO-dependent response and K(ATP)-dependent dilation.
This article was published in Br J Pharmacol
and referenced in Journal of Addiction Research & Therapy