Posttranscriptional regulation of the proximal tubule NaPi-II transporter in response to PTH and dietary P-i

Posttranscriptional regulation of the proximal tubule NaPi-II transporter i n response to PTH and dietary P-i. The rate of proximal tubular reabsorptio n of phosphate (P-i) is a major determinant of P-i homeostasis. Deviations of the extracellular concentration of P-i are corrected by many factors tha t control the activity of Na-P-i cotransport across the apical membrane. In this review, we describe the regulation of proximal tubule P-i reabsorptio n via one particular Na-P-i cotransporter (the type IIa cotransporter) by p arathyroid hormone (PTH) and dietary phosphate intake. Available data indic ate that both factors determine the net amount of type IIa protein residing in the apical membrane. The resulting change in transport capacity is a fu nction of both the rate of cotransporter insertion and internalization. The latter process is most likely regulated by PTH and dietary P-i and is cons idered irreversible since internalized type IIa Na-P-i cotransporters are s ubsequently routed to the lysosomes for degradation.