title: Effect of Ca2+ on the ouabain-insensitive, active Na+ uptake in inside-out basolateral plasma membrane vesicles from rat kidney proximal tubular cells.
abstract: 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 Marín, 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 microM. The Ka for Ca2+ (for the labile component) is around 5 microM. 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.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D006868:Hydrolysis; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008433:Mathematics; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
chemical_list: D004533:Egtazic Acid; D010042:Ouabain; D005665:Furosemide; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium