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

PRATZ, J., P. RIPQCHE, AND B. CORMAN. Cholesterol content and water and solute permeabilities of kidney membranes from aging rats. Am. J. Physiol. 253 (Regulatory Integrative Comp. Physiol. 22): R8-R14, 1987.-The influence of the age-related increase in cholesterol content of kidney brush-border membranes on their water and solute permeabilities was studied in loand 24-mo-old male Wistar rats. These permeabilities were determined from the rate of shrinkage and swelling of brushborder 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 t 40 pm/ s) and 24 mo (270 t 31 pm/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. cholesterol could be associated with significant permeability modifications. First evidence for changes in solute diffusion consecutive to an age-related rise in cholesterol was reported by Hegner (l2), who found that at between 3 and 22 mo the passive diffusion of cholic acid in rat hepatocytes decreased as plasma membrane cholesterol increased. Unfortunately, comparable data from transporting epithelia responsible for large reabsorptions of solutes and water such as nephron or intestine walls are still lacking.