Maturational Changes in Rabbit Renal Brush Border Membrane Vesicle Osmotic Water Permeability

Abstract

We have recently shown that the osmotic water permeability (Pf) of proximal tubules from neonatal rabbits is higher than that of adults (AJP 271:F871-F876, 1996). The developmental change in Pf could be due to differences in one or more of the components in the path for transepithelial water transport. The present study examined developmental changes in water transport characteristics of the proximal tubule apical membrane by determining Pf and aquaporin 1 (AQP1) expression in neonatal (10-14 days old) and adult rabbit renal brush border membrane vesicles (BBMV). AQP1 abundance in the adult BBMV was higher than the neonatal BBMV. At 25 degrees C the Pf of neonatal BBMV was found to be significantly lower than the adult BBMV at osmotic gradients from 50 to 250 mOsm/kg water. The activation energy for osmotic water movement was higher in the neonatal BBMV than the adult BBMV (9.19 +/- 0.37 vs. 5.09 +/- 0.57 kcal . deg-1 . mol-1, P < 0.005). Osmotic water movement in neonatal BBMV was inhibited 17.9 +/- 1.3% by 1 mm HgCl2 compared to 34.3 +/- 3.8% in the adult BBMV (P < 0.005). These data are consistent with a significantly greater fraction of water traversing the apical membrane lipid bilayer in proximal tubules of neonates than adults. The lower Pf of the neonatal BBMV indicates that the apical membrane is not responsible for the higher transepithelial Pf in the neonatal proximal tubule.

Maturational Changes in Rabbit Renal Basolateral Membrane Vesicle Osmotic Water Permeability

“…Thus, any difference in the calculated P f is not due to a difference in the initial vesicle size. These values were also similar to our previously reported values for BBMV (Quigley et al, 1998).…”

“…In the present study, the activation energy for the neonatal BLMV water transport was found to be the same as the adult (8.65 ± 0.47 kcal · deg −1 · mol −1 ). This is comparable to the activation energy found in the neonatal BBMV (Quigley et al, 1998). The result for the adult BLMV (8.86 ± 1.35 kcal · deg −1 · mol −1 ) is higher than that found for the BBMV value (Quigley et al, 1998), suggesting that there may be a higher fraction of water diffusing through the lipid bilayer in the basolateral membrane.…”

“…This is consistent with the finding that the membrane fluidity was higher in BLMV than BBMV (Le Grimellec et al, 1982). The present study also demonstrated that the P f of the BLMV is lower than that found in the BBMV (at 25°C BLMV: 102.6 ± 3.5 vs. BBMV: 173.4 ± 20.3 μm/sec) while the activation energy is higher (BLMV: 8.86 ± 1.35 vs. BBMV: 5.09 ± 0.57 kcal · deg −1 · mol −1 ) (Quigley et al, 1998). These differences could be due to differences in lipid composition between the apical and basolateral membranes.…”

“…The activation energies (calculated from the slopes of the lines) were 8.65 ± 0.47 kcal · deg −1 · mol −1 for the neonates and 8.86 ± 1.35 kcal · deg −1 · mol −1 for the adults (P = NS). This is in contrast to the BBMV where the neonatal membranes had a higher activation energy than the adult preparation (Quigley et al, 1998).…”

“…There is a developmental increase in the expression of AQP1 in the rat proximal tubule with minimal staining for AQP1 prior to birth and intense staining by six days of age (Bondy et al, 1993). We have recently demonstrated that there is also a developmental increase in rabbit renal brush border membrane vesicle AQP1 protein abundance and a developmental increase in osmotic water permeability (Quigley et al, 1998). Despite these maturational changes in the apical membrane, the neonatal rabbit proximal tubule has a higher transepithelial P f than the adult segment (Quigley & Baum, 1996).…”