Maturation of rabbit proximal straight tubule chloride/base exchange

Abstract

The present in vitro microperfusion study compared the mechanism and rates of NaCl transport in neonatal and adult rabbit proximal straight tubules. In proximal straight tubules perfused with a late proximal tubular fluid and bathed in a serumlike albumin solution, the rate of volume absorption (JV) 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 addition of 10(-5) M bath ouabain, JV decreased to 0.27 +/- 0.07 and -0.03 +/- 0.04 nl.mm-1.min-1 in adult and neonatal tubules, respectively (P < 0.05), consistent with lower rates of active and passive NaCl transport in the neonatal proximal straight tubule. The effect of luminal sodium and chloride removal on intracellular pH was used to 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 neonatal proximal straight tubules than adult tubules. In both neonatal and adult proximal straight tubules, the rate of Cl-/base exchange was not affected by formate, bicarbonate, or cyanide and acetazolamide, consistent with Cl-/OH- exchange. These data demonstrate an increase in proximal straight tubule NaCl transport during postnatal renal development.

Fig. 1

Effect of 10⁻⁵ M bath ouabain on adult and neonatal proximal straight tubule NaCl transport. Proximal straight tubules were perfused with a high-chloride solution simulating late proximal tubular fluid and bathed in a serumlike albumin solution. After measurements of volume absorption (J_V) in the control period, 10⁻⁵ M bath ouabain was added to the bathing solution to inhibit active transport.

Fig. 2

Proton flux rates (J_H) in response to addition of luminal sodium addition in neonatal and adult proximal straight tubules.

Fig. 3

J_H values in response to luminal chloride removal in adult and neonatal proximal straight tubules. These experiments were performed using HEPES-buffered solutions in the absence of sodium.

Fig. 4

J_H values in response to luminal chloride removal with HEPES-buffered solutions, in absence and presence of lumen and bath cyanide and acetazolamide, and with bicarbonate-buffered solutions.