Activation of dopamine D1-like receptors induces acute internalization of the renal Na+/phosphate cotransporter NaPi-IIa in mouse kidney and OK cells

Activation of dopamine D-1-like receptors induces acute internalization of the renal Na+/phosphate cotransporter NaPi-IIa in mouse kidney and OK cells. Am J Physiol Renal Physiol 288: F740-F747, 2005. First published November 16, 2004;doi:10.1152/ajprenal. 00380.2004.-The Na+/phosphate cotransporter NaPi-IIa ( SLC34A1) is the major transporter mediating the reabsorption of Pi in the proximal tubule. Expression and activity of NaPi-IIa is regulated by several factors, including parathyroid hormone, dopamine, metabolic acidosis, and dietary Pi intake. Dopamine induces natriuresis and phosphaturia in vivo, and its actions on several Na+-transporting systems such as NHE3 and Na+-K+-ATPase have been investigated in detail. Using freshly isolated mouse kidney slices, perfused proximal tubules, and cultured renal epithelial cells, we examined the acute effects of dopamine on NaPi-IIa expression and localization. Incubation of isolated kidney slices with the selective D-1-like receptor agonists fenoldopam ( 10 muM) and SKF-38393 (10 muM) for 1 h induced NaPi-IIa internalization and reduced expression of NaPi-IIa in the brush border membrane (BBM). The D-2-like selective agonist quinpirole (1 muM) had no effect. The D-1 and D-2 agonists did not affect the renal Na+/sulfate cotransporter NaSi in the BBM of the proximal tubule. Studies with isolated perfused proximal tubules demonstrated that activation of luminal, but not basolateral, D-1-like receptors caused NaPi-IIa internalization. In kidney slices, inhibition of PKC (1 muM chelerythrine) or ERK1/2 (20 muM PD-098089) pathways did not prevent the fenoldo-paminduced internalization. Inhibition with the PKA blocker H-89 (10 muM) abolished the effect of fenoldopam. Immunoblot demonstrated a reduction of NaPi-IIa protein in BBMs from kidney slices treated with fenoldopam. Incubation of opossum kidney cells transfected with NaPi-IIa-green fluorescent protein chimera shifted fluorescence from the apical membrane to an intracellular pool. In summary, dopamine induces internalization of NaPi-IIa by activation of luminal D-1-like receptors, an effect that is mediated by PKA.