* To whom correspondence should be addressed.
Received July 24, 2014; Revision received September 19, 2014
The A2B adenosine receptor (A2BR) mediates biological responses to extracellular adenosine in a wide variety of cell types. Adenosine deaminase (ADA) can degrade adenosine and bind extracellularly to adenosine receptors. Adenosine modulates chloride secretion in gastric glands and gastric mucosa parietal cells. A close functional link between surface A2BR and ADA has been found on cells of the immune system, but whether this occurs in the gastrointestinal tract is unknown. The goal of this study was to determine whether A2BR and ADA are coexpressed at the plasma membrane of the acid-secreting gastric mucosa parietal cells. We used isolated gastric parietal cells after purification by centrifugal elutriation. The membrane fraction was obtained by sucrose gradient centrifugation. A2BR mRNA expression was analyzed by RT-PCR. The surface expression of A2BR and ADA proteins was evaluated by Western blotting, flow cytometry and confocal microscopy. Our findings demonstrate that A2BR and ADA are expressed in cell membranes isolated from gastric parietal cells. They show a high degree of colocalization that is particularly evident in the surface of contact between parietal cells. The confocal microscopy data together with flow cytometry analysis suggest a tight association between A2BR and ADA that might be specifically linked to glandular secretory function.
KEY WORDS: adenosine receptor, adenosine deaminase, purine nucleoside signaling, cell membrane, gastric mucosa parietal cell