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Abstract

Basal-lateral-plasma-membrane vesicles and brush-border-membrane vesicles were isolated from rat kidney cortex by differential centrifugation followed by free-flow-electrophoresis. Ca²⁺ uptake into these vesicles was investigated by a rapid filtration method. Both membranes show a considerable binding of Ca²⁺ to the vesicle interior, making the analysis of passive fluxes in uptake experiments difficult. Only the basal-lateral-plasma-membrane vesicles exhibit an ATP-dependent pump activity which can be distinguished from the activity in mitochondrial and endoplasmic reticulum by virtue of the different distribution during free-flow electrophoresis and its lack of sensitivity to oligomycin. The basal-lateral plasma membranes contain in addition a Na⁺/Ca²⁺-exchange system which mediates a probably rheogenic counter-transport of Ca²⁺ and Na⁺ across the basal cell border. The latter system is probably involved in the secondary active Na⁺-dependent and ouabain-inhibitable Ca²⁺ reabsorption in the proximal tubule, the ATP-driven system is probably more important for the maintenance of a low concentration of intracellular Ca²⁺.