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RECEPTORS AND SIGNAL TRANSDUCTION

Adenosine receptor expression and function in bladder uroepithelium

¹Renal-Electrolyte Division and Laboratory of Epithelial Cell Biology, ³Department of Cell Biology and Physiology, and ²Department of Pharmacology and Center for Clinical Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania

Submitted 20 January 2006 ; accepted in final form 19 March 2006

The uroepithelium of the bladder forms an impermeable barrier that is maintained in part by regulated membrane turnover in the outermost umbrella cell layer. Other than bladder filling, few physiological regulators of this process are known. Western blot analysis established that all four adenosine receptors (A₁, A_2a, A_2b, and A₃) are expressed in the uroepithelium. A₁ receptors were prominently localized to the apical membrane of the umbrella cell layer, whereas A_2a, A_2b, and A₃ receptors were localized intracellularly or on the basolateral membrane of umbrella cells and the plasma membrane of the underlying cell layers. Adenosine was released from the uroepithelium, which was potentiated 10-fold by stretching the tissue. Administration of adenosine to the serosal or mucosal surface of the uroepithelium led to increases in membrane capacitance (where 1 µF 1 cm² tissue area) of 30% or 24%, respectively, after 5 h. Although A₁, A_2a, and A₃ selective agonists all stimulated membrane capacitance after being administrated serosally, only the A₁ agonist caused large increases in capacitance after being administered mucosally. Adenosine receptor antagonists as well as adenosine deaminase had no effect on stretch-induced capacitance increases, but adenosine potentiated the effects of stretch. Treatment with U-73122, 2-aminoethoxydiphenylborate, or xestospongin C or incubation in calcium-free Krebs solution inhibited adenosine-induced increases in capacitance. These data indicate that the uroepithelium is a site of adenosine biosynthesis, that adenosine receptors are expressed in the uroepithelium, and that one function of these receptors may be to modulate exocytosis in umbrella cells.

capacitance; exocytosis

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