Adenosine inhibits the renal plasma-membrane (Ca2++Mg2+)-ATPase through a pathway sensitive to cholera toxin and sphingosine

Adenosine, a potent autacoid produced and released in kidneys, affects near ly all aspects of renal function, and an increase in cytosolic calcium has been implicated in adenosine effects. The aim of this work was to investiga te whether adenosine modifies the calcium pump present in basolateral membr anes of kidney proximal tubule cells. Adenosine exerts a biphasic influence on (Ca2+ + Mg2+)-ATPase activity. Inhibition occurs up to 0.1 mu M and the n gradually disappears as the adenosine concentration increases to 100 mu M , an effect mimicked by the adenosine analog N-6-cyclohexyladenosine, which preferentially binds to A(1)-type receptors. In contrast, the A(2) recepto r agonist 5',N-ethylcarboxamideadenosine is ineffective. The A(1) receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine blocks the inhibitory effect of 0.1 mu M adenosine and stimulates (Ca2+ + Mg2+)-ATPase activity in the p resence of 1 mM adenosine, a concentration high enough to occupy the low-af finity A(2) receptors. Inhibition by adenosine increases as medium ATP is l owered to micromolar concentrations, is maintained in the presence of pertu ssis toxin, and is completely abolished with 0.1 mu M cholera toxin or 1 mu M sphingosine. The inhibitory effect of adenosine can be reproduced by gua nosine 5'-[mu-thio]triphosphate, inositol 1,4,5-trisphosphate or the diacyl glycerol analog 12-O-tetradecanoylphorbol 13-acetate. In conjunction with t he selectivity for its analogs and for its receptor agonist, the concentrat ion profile of adenosine effects indicates that both inhibitory (A(1)) and stimulatory (A(2)) receptors are involved. The results obtained with the to xins indicate that a pathway that is modulated by G-proteins, involves a ph ospholipase C and a protein kinase C, and is affected by local variations i n adenosine concentrations participates in the regulation of the (Ca2+ + Mg 2+)-ATPase resident in basolateral membranes of kidney proximal tubules.