Sodium gradient-driven transport processes in ATP-depleted renal tubules

The effects of directed Na+ gradients on proximal tubule cell transport processes were examined in suspensions of rabbit renal tubules depleted of ATP. Cells of high-Na+ content were generated by suspending the tubules in high-Na+ media, whereas low-Na+ cells were produced by incubating tubules in Na+-free media. Resuspension of the high-Na+ tubules in Na+-free media caused a fall in cell pH simultaneous with a fall in cell Na+. Resuspending the low-Na+ cells in Na+-replete media led to a rise in cell pH, in parallel with the rise in cell Na+. Removing HCO-3 and CO2 augmented and amiloride inhibited the increase in cell pH generated by the inward Na+ gradient. Low-Na+ tubules exposed to an inwardly directed Na+ gradient also concentrated the sugar analogue alpha-methylglucoside, and this uptake was blocked by phlorizin. These findings demonstrate the suitability of ATP-depleted renal tubules for the study of linked transport processes by providing evidence for the existence of the proximal luminal transport processes, Na+-H+ exchange, and Na+-sugar cotransport in this preparation.