SHORT-TERM PRIMARY CULTURES IN STUDIES OF POSTNATAL MATURATION OF THERAT PROXIMAL TUBULE - PROTON AND BICARBONATE TRANSPORT

This is a review of recent work based on an in vitro model which has a llowed us to investigate the postnatal maturation of renal epithelial cells. Renal proximal tubule cells from 8- to 40-day-old Sprague-Dawle y rats were studied after 48 h of primary culture. The regulation of i ntracellular pH (pH(i)) was measured by quantitative fluorescence micr oscopy using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Recordings were made under basal conditions and after imposing a cytop lasmic 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 o f 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 w as seen in either steady-state pH(i) (7.27-7.35) or in cytoplasmic buf fer capacity (37.6-44.4 mM/pH(i)). The characteristics of transporter maturation revealed by these experiments are very similar to those obs erved in isolated perfused proximal tubules of developing rabbits.