Basolateral membrane properties in proximal convoluted tubules of the newborn rabbit

We examined the properties of basolateral cell membranes in "immature" and "mature" proximal tubules and evaluated the possibility that changes in those membranes might contribute to the reported maturation of tubule function. Proximal convoluted tubules were dissected in connection with superficial glomeruli, crimped at both ends, and induced to swell by use of ouabain, low protein bathing medium, and/or collagenase. Tubules from adult animals swelled faster than tubules from 2- to 5- or 14- to 17-day-old animals. However, the basolateral cell membranes of tubules from adult animals were three- to fourfold larger in surface area than those from 2- to 17-day animals, so that the ratio of the swelling rates to the measured basolateral membrane areas remained constant during the period from newborn to adult. We conclude that the basolateral membranes "mature" only in their surface areas and that little change occurs in their intrinsic properties such as hydraulic conductivity or ion permeability.