ATP RECEPTOR REGULATION OF ADENYLATE-CYCLASE AND PROTEIN-KINASE-C ACTIVITY IN CULTURED RENAL LLC-PK1 CELLS

In cultured intact LLC-PK1 renal epithelial cells, a nonhydrolyzable ATP analogue, ATP-gamma-S, inhibits AVP-stimulated cAMP formation. In LLC-PK1 membranes, several ATP analogues inhibit basal, GTP-, forskolin-, and AVP-stimulated adenylate cyclase activity in a dose-dependent manner. The rank order potency of inhibition by ATP analogues suggests that a P2y type of ATP receptor is involved in this inhibition. The compound ATP-gamma-S inhibits agonist-stimulated adenylate cyclase activity in solubilized and in isobutylmethylxanthine (IBMX) and quinacrine pretreated membranes, suggesting that ATP-gamma-S inhibition occurs independent of AVP and A1 adenosine receptors and of phospholipase A2 activity. The ATP-gamma-S inhibition of AVP-stimulated adenylate cyclase activity is not affected by pertussis toxin but is attenuated by GDP-beta-S, suggesting a possible role for a pertussis toxin insensitive G protein in the inhibition. Exposure of intact LLC-PK cells to ATP-gamma-S results in a significant increase in protein kinase C activity. However, neither of two protein kinase C inhibitors (staurosporine and H-7) prevents ATP-gamma-S inhibition of AVP-stimulated adenylate cyclase activity, suggesting that this inhibition occurs by a protein kinase C independent mechanism. These findings suggest the presence of functional P2y purinoceptors coupled to two signal transduction pathways in cultured renal epithelial cells. The effect of P2y purinoceptors to inhibit AVP-stimulated adenylate cyclase activity may be mediated, at least in part, by a pertussis toxin insensitive G protein.