Cation flux in the ehrlich ascites tumor cell. Evidence for Na+-for-Na+ and K+-for-K+ exchange diffusion.
In a previous study, evidence was presented for an external Na+-dependent, ouabain-insensitive component of Na+ efflux and an external K+-dependent component of K+ efflux in the Ehrlich ascites tumor cell. Evidence is now presented that these components are inhibited by the diuretic furosemide and that under conditions of normal extracellular Na+ and K+ they represent Na+-for-Na+ and K-+for-K+ exchange mechanisms. Using 86Rb to monitor K+ movements, furosemide is shown to inhibit an ouabain-insensitive component of Rb+ influx and a component of Rb+ efflux, both representing approx. 30 percent of the total flux. Inhibition of Rb+ efflux is greatly reduced by removal of extracellular K+. Furosemide does not alter steady-state levels of intracellular K+ and it does not prevent cells depleted of K+ by incubation in the cold from regaining K+ upon warming. Using 22Na to monitor Na+ movements, furosemide is shown to inhibit an ouabain-insensitive component of unidirectional Na+ efflux which represents approx. 22 percent of total Na+ efflux. Furosemide does not alter steady-state levels of intracellular Na+ and does not prevent removal of intracellular Na+ upon warming from cells loaded with Na+ by preincubation in the cold. The ability of furosemide to affect unidirectional Na+ and K+ fluxes but not net fluxes is consistent with the conclusion that these components of cation movement across the cell membrane represent one-for-one exchange mechanisms. Data are also presented which demonstrate that the uptake of alpha-aminoisobutyrate is not affected by furosemide. This indicates that these components of cation flux are not directly involved in the Na+-dependent amino acid transport system A.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003864:Depression, Chemical; D004058:Diffusion; D004305:Dose-Response Relationship, Drug; D005665:Furosemide / Q000494:pharmacology; D051379:Mice; D008813:Mice, Inbred ICR; D009368:Neoplasm Transplantation; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D000596:Amino Acids; D010042:Ouabain; D005665:Furosemide; D012964:Sodium; D012413:Rubidium; D011188:Potassium