ATP receptor regulation of adenylate cyclase and protein kinase C activity in cultured renal LLC-PK 1 cells

In cultured intact LLC-PK, renal epithelial cells, a nonhydro-lyzable ATP analogue, ATPyS, inhibits AVP-stimulated cAMP formation. In LLC-PK, membranes, several ATP ana-logues inhibit basal, GTP-, forskolin-, and AVP-stimulated ade-nylate 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 ATPyS inhibits agonist-stimulated adenylate cy-clase activity in solubilized and in isobutylmethylxanthine (IBMX) and quinacrine pretreated membranes, suggesting that ATP'yS inhibition occurs independent of AVP and Al adeno-sine receptors and of phospholipase A2 activity. The ATP'yS inhibition of AVP-stimulated adenylate cyclase activity is not affected by pertussis toxin but is attenuated by GDP#S, sug-gesting a possible role for a pertussis toxin insensitive G pro-tein in the inhibition. Exposure of intact LLC-PK cells to ATP'yS results in a significant increase in protein kinase C activity. However, neither of two protein kinase C inhibitors (staurosporine and H-7) prevents ATP'yS inhibition of AVP-stimulated adenylate cyclase activity, suggesting that this inhi-bition occurs by a protein kinase C independent mechanism. These findings suggest the presence of functional P2y purino-ceptors 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. (J. Clin