Phosphate transport across renal proximal tubular cell membranes.

The transport of phosphate across the plasma membrane of the renal proximal tubular epithelial cell is thought to take place through the activities of specific transporters located in the membrane. The activities of these transporters are essential to effect the reabsorption of phosphate present in glomerular ultrafiltrate. In addition, their activities are thought to be important for the maintenance of metabolic functions in the proximal tubular cell. Studies utilizing proximal tubular brush-border and basolateral membranes isolated from mammalian kidney have provided significant insights into the mechanisms by which phosphate transport across the brush-border and basolateral membranes of the intact proximal tubular cell occurs and is modulated. In this editorial review, the results of many of these studies are summarized. Particular emphasis is placed on studies that utilized isolated membranes to determine the mechanism by which the phosphaturic action of parathyroid hormone is mediated in the renal proximal tubule. On the basis of studies conducted in isolated membranes and in more physiologically intact preparations, models are constructed to integrate the role of the brush-border and basolateral membranes in the transport of phosphate into and out of the renal proximal tubular cell.