Regulation of transepithelial phosphate transport by PTH in chicken proximal tubule epithelium

Abstract

The effect of parathyroid hormone (PTH) and activation of protein kinase C (PKC) and protein kinase A (PKA) on transepithelial Pi transport was examined in monolayers of chick proximal tubule cells in primary culture (PTCs). Acute exposure of the PTCs to PTH (10−9 M, basolateral side) significantly decreased the net reabsorption of Pi by ∼66%. There was no effect after the addition of PTH to the luminal side. Activation of PKC by phorbol 12-myristate 13-acetate (PMA; 0.1 μM) dramatically decreased net Pi reabsorption by ∼60%. Bisindolylmaleimide I (BIM; 1 μM), a highly selective PKC inhibitor, prevented PMA-induced inhibition. Activation of adenylate cyclase/PKA by forskolin (10 μM) mimicked the effect of PTH by significantly reducing net Pi reabsorption by one-half. Addition of H-89 (10 μM), a potent inhibitor of PKA, abolished forskolin-induced inhibition. PTH inhibition was blocked by either BIM or H-89. Tissue electrophysiology remained stable after all treatments. There was a decreased immunoreactivity of the luminal Na+-Pi cotransporter NaPi-IIa after PTH treatment. These data indicate that PTH inhibition of Pireabsorption in this in vitro system is mediated by PKC and PKA.