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Effect of Ca2+ on the ouabain-insensitive, active Na+ uptake in inside-out basolateral plasma membrane vesicles from rat kidney proximal tubular cells

1985; Elsevier BV; Volume: 817; Issue: 2 Linguagem: Inglês

10.1016/0005-2736(85)90031-8

1879-2642

Reinaldo Marı́n, Teresa Proverbio, Fulgencio Proverbio,

Membrane-based Ion Separation Techniques

The ouabain-insensitive, active Na+ uptake of inside-out vesicles prepared with basolateral plasma membranes from rat kidney proximal tubular cells can be increased by the presence of micromolar concentrations of Ca2+ in the assay medium. The concomitant ATP hydrolysis associated with the Na+ uptake is also increased by the presence of Ca2+. The Na+ uptake and the concomitant ATP hydrolysis are inhibited by 2 mM furosemide. The effect of Ca2+ is not due to the activity of an Na+-Ca2+ exchanger. The present results are in accordance with our previous model (Proverbio, F., Proverbio, T. and Marin, R. (1982) Biochim. Biophys. Acta 688, 757–763) in which we proposed that Ca2+ seems to modulate the activity of the ouabain-insensitive Na+ pump, in two different ways: (1) in a strong association with the membranes in which Ca2+ (stable component) is essential for the pump activity and (2) in a weak association with the membranes in which Ca2+ (labile component) can be quickly and easily removed by reducing the free Ca2+ concentration of the assay medium to values lower than 1 μM. The Ka for Ca2+ (for the labile component) is around 5 μM. The Ca2+ modulation of the ouabain-insensitive Na+ pump is an indication that Ca2+ could regulate the magnitude of the Na+ extrusion accompanied by Cl− and water present in rat kidney proximal tubular cells.