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

A common feature of sodium-reabsorbing epithelia is their ability to m atch salt entry to salt exit. It is recognized that a key strategy to perform this feat involves the coupling between basolateral sodium pum p and potassium conductance (pump-leak coupling). In the renal proxima l tubule this coupling is of major importance, as regions of this neph ron segment are faced with ever-changing reabsorptive loads. An unders tanding of this coupling can be facilitated by critically examining th ose studies that have looked at the problem from the point of view of the whole cell (macroscopic studies) and of single channels (microscop ic studies). An overview of such work suggests that the transduction m echanisms which are likely to effect pump-leak coupling in the renal p roximal tubule involve cell volume, ATP, and pH (but not calcium). Alt hough the relationship between ATP and potassium conductance may be re latively straightforward, the involvement of pH is likely to be only t ransient and that of volume remains controversial, occurring either di rectly though stretch-activated channels in amphibian preparations or indirectly through an as yet unidentified second messenger system in m ammalian preparations.