ABSTRACT
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 proximal tubules through the generation of an increase in intracellular arachidonic acid, followed by its conversion to 20-hydroxyeicosatetraenoic 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. Ribeiro, G. Dubay, J. R. Falk, and L. J. Mandel. Am. J. Physiol. 266 (Renal Fluid Electrolyte Physiol. 35): F497-F505, 1994]. The present study also uses proximal tubule suspensions to further elucidate this signaling pathway. Guanosine 5'-O-(2-thiodiphosphate), 500 microM, an inhibitor of heterotrimeric GTP-binding proteins (G proteins), and an anti-Gq/G11 antibody (1:500) both blocked the inhibition of the Na(+)-K(+)-ATPase by PTH-(3-34). Furthermore, a 42-kDa protein was identified in proximal tubules by the anti-Gq/G11 antibody (1:1,000). Bromoenol lactone (BEL), 1 microM, a suicide inhibitor of the calcium-independent 40-kDa phospholipase A2 (PLA2), prevented PTH-(3-34) inhibition of the Na(+)-K(+)-ATPase, unless exogenous 10 microM 20-HETE was added. In addition, BEL blocked the PTH-(3-34)-induced increase in arachidonic acid release in the proximal tubules. We conclude that a member of the Gq family and the calcium-independent 40-kDa PLA2 participate in the PTH-(3-34) signaling pathway in rat proximal tubules by mediating the steps between the binding of PTH-(3-34) to its receptor and the subsequent generation of arachidonic acid.
