MATURATION OF RABBIT PROXIMAL STRAIGHT TUBULE CHLORIDE BASE EXCHANGE/

The present in vitro microperfusion study compared the mechanism and r ates of NaCl transport in neonatal and adult rabbit proximal straight tubules. In proximal straight tubules perfused with a late proximal tu bular fluid and bathed in a serumlike albumin solution, the rate of vo lume absorption (J(v)) was 0.54 +/- 0.10 and 0.12 +/- 0.05 nl . mm(-1) . min(-1) in adults and neonates, respectively (P < 0.05). With the a ddition of 10(-5) M bath ouabain, J(v) decreased to 0.27 +/- 0.07 and -0.03 +/- 0.04 nl . mm(-1) . min(-1) in adult and neonatal tubules, re spectively (P < 0.05), consistent with lower rates of active and passi ve NaCl transport in the neonatal proximal straight tubule. The effect of luminal sodium and chloride removal on intracellular pH was used t o assess the relative rates of Na+/H+ and Cl-/base exchange. The rates of Na+/H+ and Cl-/base exchange were approximately fivefold less in n eonatal proximal straight tubules than adult tubules. In both neonatal and adult proximal straight tubules, the rate of Cl-/base exchange wa s not affected by formate, bicarbonate, or cyanide and acetazolamide, consistent with Cl-/OH- exchange. These data demonstrate an increase i n proximal straight tubule NaCl transport during postnatal renal devel opment.