This report describes studies on the biochemical, biophysical, and physiological mechanisms of membrane transport in the kidney, the regulation of these transport systems by hormones and various pathophysiological effectors, and the changes which occur in renal function in aging. The findings relate to investigations on: (a) Sodium-proton exchange activity, adaptation in metabolic acidosis and regulation by hormones. (b) Titratable acid (phosphate) excretion in response to metabolic acidosis. (c) Characterization of the sodium-protein exchange carrier. (d) Cell culture systems for examining the mechanisms of hormonal regulation. (e) Chronic renal insufficiency and the pathogenesis of progressive glomerular sclerosis in aging. (f) Sodium-dependent transport of inorganic sulfate in renal brush border membranes (g) Renal transport in the diabetic (streptozotocin-treated) rat: transport of Beta-hydroxybutyrate in the ketotic animal. (h) Identification and characterization of ion channels in epithelial cells: hormonal regulation. (i) Phospholipid and calcium-dependent protein kinase (Protein kinase C). (j) Distinctive microdomains in the kidney proximal tubule brush border membrane.