Correlation between fluid reabsorption and proximal tubule ultrastructure during development of the rat kidney

Abstract

Parallel functional and ultrastructural studies were performed in maturing rats to elucidate factors determining the development of proximal tubular fluid reabsorption. Three groups of hydropenic animals, which were 22-24, 28-32 and 40-45 days old, were studied. Nephron function was evaluated at the single nephron level by micropuncture technique. The ultrastructure of the developing proximal tubules was analyzed by morphometric techniques following fixation of single nephrons. Kidney wt, proximal convoluted tubule length and diameter increased during postnatal development. SNGFR [single nephron glomerular filtration rate] increased from 2.98-8.57 and to 20.5 nl/min in respective group of rats whereas proximal tubular fluid reabsorption Jv (a) increased from 0.15-0.22 and 0.34 .mu.m3/.mu.m .cntdot. s. Parallel to the functional development, the relative area of lateral and basal cell membrane increased, resulting in a constant relationship between net fluid reabsorption and the lateral and basal cell membrane area during the 4th postnatal wk, and then only a slight increase in this relation during the further development. Net fluid transport during hydropenia is determined by the amount of available lateral and basal cell membranes where the transporting enzyme for Na is located.