Submitted on July 3, 2007
Accepted on October 2, 2007
Involvement of COX-1 in A3 adenosine receptor-mediated contraction through endothelium in mice aorta
Habib R. Ansari1, Ahmed Nadeem1, Stephen L. Tilley2, and S. Jamal Mustafa1*
1 Physiology and Pharmacology, West Virginia University, Morgantown, West Virginia, United States
2 Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, United States
* To whom correspondence should be addressed. E-mail: smustafa{at}hsc.wvu.edu.
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 knock-out (A3KO) mice aorta. A3AR selective agonist, Cl-IBMECA produced a concentration-dependent contraction (EC50: 2.9±0.2x10-9 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) both in WT and A3KO aorta. A3AR gene and protein expression were reduced by 74% and 72% (p<0.05), respectively in WT (-E) as compared to WT (+E) aorta while being undetected in A3KO (+E/-E) aorta. Indomethacin (non-specific COXs blocker, 10-5 M), SC-560 (specific COX-1 blocker, 10-8 M), SQ 29549 [thromboxane prostanoid receptor (TP) antagonist (10-6 M)] and furegrelate [thromboxane synthase (TS) inhibitor, 10-5 M] inhibited Cl-IBMECA-induced contraction significantly. Cl-IBMECA-induced TXB2 production was 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 both in WT (+E) and A3KO (+E) aorta. Cl-IBMECA-induced increase in COX-1 and TP receptor expression was 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.
