title: (Na+,K+)-cotransport in the Madin-Darby canine kidney cell line. Kinetic characterization of the interaction between Na+ and K+.
abstract: Confluent monolayer cultures of the differentiated kidney epithelial cell line, Madin-Darby canine kidney cells (MDCK), have been used to study ion transport mechanisms involved in transepithelial transport. We have investigated the previously reported K+-stimulation of 22Na+ uptake by confluent monolayers of Na+ depleted cells (Rindler, M. J., Taub, M., and Saier, M. H., Jr. (1979) J. Biol. Chem. 254, 11431-11439). This component of Na+ uptake was insensitive to ouabain and amiloride, but was strongly inhibited by furosemide or bumetanide. Ouabain-insensitive 86Rb+ uptake was also inhibitable by furosemide or bumetanide and stimulated by extracellular Na+. The synergistic effect of Na+ and 86Rb+ uptake and K+ on 22Na+ uptake was reflected by an increase in the apparent Vmax and a decrease in the apparent Km as the concentration of the other cation was increased. The extrapolated Km for either 86Rb+ or 22Na+ uptake in the absence of the other cation was 30 mM while the Km in the presence of a saturating concentration of the other cation was 9 mM. The absolute Vmax values for 22Na+ and 86Rb+ uptake suggest a cotransport system with a stoichiometry of 2Na+:3K+. However, because of the experimental design, the actual ratio may be closer to 1:1. Competition with, and stimulation by, a variety of unlabeled cations indicated that Na+ could be partially replaced by Li+, while K+ could be fully replaced by Rb+ and partially replaced by NH4+ and CS+. Uptake by this system was dependent upon cellular ATP. Reduction of intracellular ATP to 3% of normal abolished both K+-stimulated 22Na+ uptake and Na+-stimulated 86Rb+ uptake.
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002460:Cell Line; D004285:Dogs; D005665:Furosemide / Q000494:pharmacology; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D002034:Bumetanide; D010042:Ouabain; D000584:Amiloride; D005665:Furosemide; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium