PARATHYROID-HORMONE INHIBITS NA-K+-ATPASE THROUGH G(Q)()G(11) AND THECALCIUM-INDEPENDENT PHOSPHOLIPASE A(2)/

Previous studies from this laboratory have demonstrated that the 3-34 analog of parathyroid hormone (PTH) causes a 15-30% inhibition of Na+- K+-adenosinetriphosphatase (Na+-K+ ATPase) activity in rat renal proxi mal tubules through the generation of an increase in intracellular ara chidonic acid, followed by its conversion to 20-hydroxyeicosatetraenoi c acid (20-HETE) [C. P. Ribeiro and L. J. Mandel. Am. J. Physiol. 262 (Renal Fluid Electrolyte Physiol. 31): F209-F216, 1992; and C. P. Ribe iro, G. Dubay, J. R. Falk, and L. J. Mandel. Am. J. Physiol. 266 (Rena l Fluid Electrolyte Physiol. 35): F497F505, 1994]. The present study a lso uses proximal tubule suspensions to further elucidate this signali ng pathway. Guanosine 5'-O-(2-thiodiphosphate), 500 mu M, an inhibitor of heterotrimeric GTP-binding proteins (G proteins), and an anti-G(q) /G(11) antibody (1:500) both blocked the inhibition of the Na+-K+-ATPa se by PTH-(3-34). Furthermore, a 42-kDa protein was identified in prox imal tubules by the anti-G(q)/G(11) antibody (1:1,000). Bromoenol lact one (EEL), 1 mu M, a suicide inhibitor of the calcium-independent 40-k 13a phospholipase A(2) (PLA(2)), prevented PTH-(8-34) inhibition of th e Na+-K+-ATPase, unless exogenous 10 mu M 80-HETE was added. In additi on, EEL blocked the PTH-(3-34)-induced increase in arachidonic acid re lease in the proximal tubules. We conclude that a member of the G(q) f amily and the calcium-independent 40-kDa PLA(2) participate in the PTH -(3-34) signaling pathway in rat proximal tubules by mediating the ste ps between the binding of PTH-(3-34) to its receptor and the subsequen t generation of arachidonic acid.