CYP-epoxygenases contribute to A2A receptor-mediated aortic relaxation via sarcolemmal KATP channels

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 303; no. 10; pp. R1003 - R1010
• Main Authors: Ponnoth, Dovenia S, Nayeem, Mohammed A, Tilley, Stephen L, Ledent, Catherine, Jamal Mustafa, S
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 15.11.2012
• Subjects: Adenosine - analogs & derivatives; Adenosine - pharmacology; Adenosine-5'-(N-ethylcarboxamide) - pharmacology; Alcohol Oxidoreductases - physiology; Animals; Cardiovascular and Renal Integration; Cromakalim; Decanoic Acids - pharmacology; Female; Glyburide - pharmacology; Hydroxy Acids - pharmacology; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Oxidoreductases - genetics; Oxidoreductases - metabolism; Phenethylamines - pharmacology; Pinacidil; Receptor, Adenosine A2A - metabolism; Sarcolemma - physiology
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00335.2012

Previously, we have shown that A(2A) adenosine receptor (A(2A)AR) mediates aortic relaxation via cytochrome P-450 (CYP)-epoxygenases. However, the signaling mechanism is not understood properly. We hypothesized that ATP-sensitive K(+) (K(ATP)) channels play an important role in A(2A)AR-mediated relaxation. Organ bath and Western blot experiments were done using isolated aorta from A(2A)KO and corresponding wild-type (WT) mice. Aortic rings from WT and A(2A) knockout (KO) mice were precontracted with submaximal dose of phenylephrine (PE, 10(-6) M), and concentration-response curves for pinacidil, cromakalim (nonselective K(ATP) openers), and diazoxide (mitochondrial K(ATP) opener) were obtained. Diazoxide did not have any relaxation effect on PE-precontracted tissues, whereas relaxation to pinacidil (48.09 ± 5.23% in WT vs. 25.41 ± 2.73% in A(2A)KO; P < 0.05) and cromakalim (51.19 ± 2.05% in WT vs. 38.50 ± 2.26% in A(2A)KO; P < 0.05) was higher in WT than A(2A)KO aorta. This suggested the involvement of sarcolemmal rather than mitochondrial K(ATP) channels. Endothelium removal, treatment with SCH 58651 (A(2A)AR antagonist; 10(-6) M), N(G)-nitro-l-arginine methyl ester (l-NAME, nitric oxide synthase inhibitor) and methylsulfonyl-propargyloxyphenylhexanamide (MS-PPOH, CYP-epoxygenases inhibitor; 10(-5) M) significantly reduced pinacidil-induced relaxation in WT compared with controls, whereas these treatments did not have any effect in A(2A)KO aorta. Glibenclamide (K(ATP) channel inhibitor, 10(-5) M) blocked 2-p-(2-carboxyethyl)phenethylamino-5'N-ethylcarboxamido adenosine hydrochloride (CGS 21680, A(2A)AR agonist)-induced relaxation in WT and changed 5'-N-ethylcarboxamide (NECA) (nonselective adenosine analog)-induced response to higher contraction in WT and A(2A)KO. 5-Hydroxydecanoate (5-HD, mitochondrial K(ATP) channel inhibitor, 10(-4) M) had no effect on CGS 21680-mediated response in WT aorta. Our data suggest that A(2A)AR-mediated vasorelaxation occurs through opening of sarcolemmal K(ATP) channels via CYP-epoxygenases and possibly, nitric oxide, contributing to pinacidil-induced responses.