Involvement of COX-1 in A3 adenosine receptor-mediated contraction through endothelium in mice aorta

We investigated whether A3 adenosine receptor (A3AR) is involved in endothelium-mediated contraction through cyclooxygenases (COXs) with the use of wild-type (WT) and A3 knockout (A3KO) mice aorta. A3AR-selective agonist, Cl-IBMECA, produced a concentration-dependent contraction (EC50: 2.9 ± 0.2 × 10−9 M) in WT mouse aorta with intact endothelium (+E) and negligible effects in A3KO +E aorta. At 10−7 M, contractions produced by Cl-IBMECA were 29% in WT +E, while being insignificant in A3KO +E aorta. Cl-IBMECA-induced responses were abolished in endothelium-denuded tissues (−E), in both WT and A3KO aorta. A3AR gene and protein expression were reduced by 74 and 72% ( P < 0.05), respectively, in WT −E compared with WT +E aorta, while being undetected in A3KO +E/−E aorta. Indomethacin (nonspecific COXs blocker, 10−5 M), SC-560 (specific COX-1 blocker, 10−8 M), SQ 29549 (thromboxane prostanoid receptor antagonist, 10−6 M), and furegrelate (thromboxane synthase inhibitor, 10−5 M) inhibited Cl-IBMECA-induced contraction significantly. Cl-IBMECA-induced thromboxane B2 production was also attenuated significantly by indomethacin, SC-560, and furegrelate in WT +E aorta, while having negligible effects in A3KO +E aorta. NS-398 (specific COX-2 blocker) produced negligible inhibition of Cl-IBMECA-induced contraction in both WT +E and A3KO +E aorta. Cl-IBMECA-induced increase in COX-1 and thromboxane prostanoid receptor expression were significantly inhibited by MRS1523, a specific A3AR antagonist in WT +E aorta. Expression of both A3AR and COX-1 was located mostly on endothelium of WT and A3KO +E aorta. These results demonstrate for the first time the involvement of COX-1 pathway in A3AR-mediated contraction via endothelium.