COUPLING BETWEEN TRANSEPITHELIAL NA-TRANSPORT AND BASOLATERAL K-CONDUCTANCE IN RENAL PROXIMAL TUBULE

A common feature of sodium-reabsorbing epithelia is their ability to match salt entry to salt exit. It is recognized that a key strategy to perform this feat involves the coupling between basolateral sodium pump and potassium conductance (pump-leak coupling). In the renal proximal tubule this coupling is of major importance, as regions of this nephron segment are faced with ever-changing reabsorptive loads. An understanding of this coupling can be facilitated by critically examining those studies that have looked at the problem from the point of view of the whole cell (macroscopic studies) and of single channels (microscopic studies). An overview of such work suggests that the transduction mechanisms which are likely to effect pump-leak coupling in the renal proximal tubule involve cell volume, ATP, and pH (but not calcium). Although the relationship between ATP and potassium conductance may be relatively straightforward, the involvement of pH is likely to be only transient and that of volume remains controversial, occurring either directly though stretch-activated channels in amphibian preparations or indirectly through an as yet unidentified second messenger system in mammalian preparations.