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Articles in PresS, published online ahead of print November 29, 2001
Am J Physiol Heart Circ Physiol, 10.1152/ajpheart.00808.2001
Submitted on September 13, 2001
Accepted on November 15, 2001
1 Physiology, University of Kentucky, Lexington, KY, USA
2 Surgery, University of Kentucky, Lexington, KY, USA
3 Surgery, University of Kentucky, Lexington, KY, USA; Physiology, University of Kentucky, Lexington, KY, USA
* To whom correspondence should be addressed. E-mail: elkilp0{at}pop.uky.edu.
Adenosine A2a receptors are found in coronary vascular tissue while its presence in myocardium is subject to investigation. Although there have been numerous studies on adenosine A2a receptor agonist effects on contractility and cAMP levels in ventricular myocytes, these have yielded conflicting results. Negative pharmacological studies have even led to the conclusion that A2a receptors are not present in cardiac myocytes. The purpose of this study was to determine whether A2a receptors were expressed in rat ventricular myocytes, and what physiological effects were mediated via activation of these receptors. Western blot analysis, using a polyclonal antibody raised against a peptide sequence specific to the carboxyterminus of the A2a receptor, revealed the presence of a band at ~ 45 kDa. However, the immunoreactivity was located in the non-membrane fraction of the cell lysate. The membrane fraction only exhibited an immunoreactive band 
50 kDa. Treatment of isolated myocytes with the adenosine A2a agonist 2-[4-[(2-carboxyethyl)-phenyl]ethylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680) exerted no effects on cAMP levels or myocyte twitch amplitude. These results indicate that although rat ventricular myocytes appear to express adenosine A2a receptors, stimulation with an A2a agonist exerts no functional effects, possibly due to the subcellular localization of the A2a receptor.
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