Short-term primary cultures in studies of post-natal maturation of the rat proximal tubule-proton and bicarbonate transport.

This is a review of recent work based on an in vitro model which has allowed us to investigate the postnatal maturation of renal epithelial cells. Renal proximal tubule cells from 8- to 40-day-old Sprague-Dawley rats were studied after 48 h of primary culture. The regulation of intracellular pH (pHi) was measured by quantitative fluorescence microscopy using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Recordings were made under basal conditions and after imposing a cytoplasmic alkalosis or acidosis using 15 mM ammonium salt. The ability of the cells to recover from both acidosis and alkalosis improved during post-natal maturation. The improvement in recovery from intracellular acidosis could be entirely accounted for by an increase in the rate of Na+/H+ exchange. The capacity for Na+/H+ exchange was independent of the cellular growth rate, but depended on cellular differentiation. A developmental increase in the activity of Cl-/HCO3- exchange between 12 and 14 days of age was also demonstrated. No developmental change was seen in either steady-state pHi (7.27-7.35) or in cytoplasmic buffer capacity (37.6-44.4 mM/pHi). The characteristics of transporter maturation revealed by these experiments are very similar to those observed in isolated perfused proximal tubules of developing rabbits.