Cholesterol content and water and solute permeabilities of kidney membranes from aging rats

The influence of the age-related increase in cholesterol content of kidney brush-border membranes on their water and solute permeabilities was studied in 10- and 24-mo-old male Wistar rats. These permeabilities were determined from the rate of shrinkage and swelling of brush-border vesicles using a stopped-flow apparatus coupled to a light transmission recording. Despite a 20% rise in total cholesterol per milligram proteins, the osmotic water permeabilities of the vesicles were unchanged between 10 (287 +/- 40 micron/s) and 24 mo (270 +/- 31 micron/s). In contrast, passive diffusions of NaCl and KCl, but not of urea, thiourea, and glycerol, were reduced by 35% between 10 and 24 mo. These results suggest that an increase in cholesterol content of kidney brush-border membrane decreases its salt permeabilities without altering the water pathways.