DEVELOPMENTAL-CHANGES IN RABBIT JUXTAMEDULLARY PROXIMAL CONVOLUTED TUBULE ACIDIFICATION

The transporters responsible for apical proton secretion were examined in neonatal and adult proximal convoluted tubules (PCT). transporter activity was assayed from the rate of recovery of cell pH after cell a cidification following exposure to NH4Cl. Cell pH was monitored in in vitro perfused tubules using the pH sensitive dye 2',7'-bis(carboxyeth yl)-5,6-carboxyfluorescein. Recovery from an acid load in adult PCT oc curred at 0.52 +/- 0.09 pH units/min in the presence of sodium and 0.2 5 +/- 0.05 in the absence of sodium (p < 0.05). One mmol/L, N-ethylmal eimide, an inhibitor of the H+-ATPase, inhibited the sodium-independen t pH recovery from an acid load consistent with a H+-ATPase on the api cal membrane. In neonatal PCT, recovery from an acid load was 0.39 +/- 0.08 pH units/min in the presence of sodium and only 0.08 pH units/mi n in the absence of sodium (p < 0.05). Studies using 4 mmol/L luminal amiloride, an inhibitor of the Na+/H+ antiporter, were consistent with a larger fraction of pH recovery from an acid load in neonatal PCT be ing due to the Na+/H+ antiporter compared with adult PCT. Thus, matura tion of the PCT involves an increase in activity of a sodium-independe nt proton secretory mechanism, presumably the H+-ATPase.