Abstract

The effect of adenosine on Na⁺/H⁺ exchange activity was examined in cultured A₆ renal epithelial cells. Adenosine and its analogue N⁶-cyclopentyladenosine (CPA) had different effects on Na⁺/H⁺ exchange activity depending on the side of addition. Basolateral CPA induced a stimulation of Na⁺/H⁺ exchange activity that was completely prevented by preincubation with an A_2A-selective antagonist, 8-(3-chlorostyryl)caffeine, whereas apical CPA induced a slight but significant inhibition of Na⁺/H⁺ exchange activity that was significantly reduced by the A₁-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine. Protein kinase C activation may be involved in mediating the apical CPA inhibition of Na⁺/H⁺ exchange activity; this inhibition was prevented by the protein kinase C inhibitor calphostin C. Treatment with either forskolin or 8-bromo-cAMP significantly stimulated Na⁺/H⁺ exchange activity; only basolateral CPA addition induced an increase in cAMP level. These observations together with the finding that the CPA-dependent stimulation of exchange activity was prevented by the protein kinase A inhibitor H-89 support the hypothesis that basolateral CPA stimulates Na⁺/H⁺ exchange via adenylate cyclase/protein kinase A activation. Basolateral CPA also increased transepithelial Na⁺ transport, and this stimulation was prevented by the Na⁺/H⁺ exchange inhibitor HOE-694, suggesting that changes in pH_i during hormone action can act as an intermediate in the second-messenger cascade.