Maturational changes in rabbit renal basolateral membrane vesicle osmotic water permeability

We have recently demonstrated that while the osmotic water permeability (P- f) of neonatal proximal tubules is higher than that of adult tubules, the P -f of brush-border membrane vesicles from neonatal rabbits is lower than th at of adults. The present study examined developmental changes in the water transport characteristics of proximal tubule basolateral membranes by dete rmining aquaporin 1 (AQP1) protein abundance and the P-f in neonatal (10-14 days old) and adult rabbit renal basolateral membrane vesicles (BLMV). At 25 degrees C the P-f of neonatal BLMV was significantly lower than the adul t BLMV at osmotic gradients ranging from 40 to 160 mOsm/kg water. The activ ation energies for osmotic water movement were identical in the neonatal an d adult BLMV (8.65 +/- 0.47 vs. 8.86 +/- 1.35 kcal . deg(-1) . mol(-1)). Re flection coefficients for sodium chloride and sodium bicarbonate were ident ical in both the neonatal and adult BLMV and were not different from one. M ercury chloride (0.5 mM) reduced osmotic water movement by 31.3 +/- 5.5% in the adult BLMV, but by only 4.0 +/- 4.0% in neonatal vesicles (P < 0.01). Adult BLMV AQP1 abundance was higher than that in the neonate. These data d emonstrate that neonatal BLMV have a lower P-f and AQP1 protein abundance t han adults and that a significantly greater fraction of water traverses the basolateral membrane lipid bilayer and not water channels in neonates comp ared to adults. The lower P-f of the neonatal BLMV indicates that the basol ateral membrane is not responsible for the higher transepithelial P-f in th e neonatal proximal tubule.