Increase of Na+ gradient-dependent L-glutamate and L-aspartate transport in high K+ dog erythrocytes associated with high activity of (Na+, K+)-ATPase.
As reported previously, some dogs possess red cells characterized by low Na+, high K+ concentrations, and high activity of (Na+, K+)-ATPase, although normal dog red cells contain low K+, high Na+, and lack (Na+, K+)-ATPase. Furthermore, these red cells show increased activities of L-glutamate and L-aspartate transport, resulting in high accumulations of such amino acids in their cells. The present study demonstrated: (i) Na+ gradient-dependent L-glutamate and L-aspartate transport in the high K+ and low K+ red cells were dominated by a saturable component obeying Michaelis-Menten kinetics. Although no difference of the Km values was observed between the high K+ and low K+ cells, the Vmax values for both amino acids' transport in the high K+ cells were about three times those of low ones. (ii) L- and D-aspartate, but not D-glutamate, competitively inhibited L-glutamate transport in both types of the cells. (iii) Ouabain decreased the uptake of the amino acids in the high K+ dog red cells, whereas it was not effective on those in the low K+ cells. (iv) The ATP-treated high K+ cells [(K+]i not equal to [K+]o, [Na+]i greater than [Na+]o) showed a marked decrease of both amino acids' uptake rate, which was almost the same as that of the low K+ cells. (v) Valinomycin stimulated the amino acids' transport in both of the high K+ and the ATP-treated low K+ cells [( K+]i greater than [K+]o, [Na+]o), suggesting that the transport system of L-glutamate and L-aspartate in both types of the cells might be electrogenic. These results indicate that the increased transport activity in the high K+ dog red cells was a secondary consequence of the Na+ concentration gradient created by (Na+, K+)-ATPase.
D000818:Animals; D001224:Aspartic Acid / Q000097:blood*; D001693:Biological Transport, Active; D004285:Dogs; D004912:Erythrocytes / Q000378:metabolism*; D005971:Glutamates / Q000097:blood*; D018698:Glutamic Acid; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood*; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood*; D014634:Valinomycin / Q000494:pharmacology
D005971:Glutamates; D014634:Valinomycin; D001224:Aspartic Acid; D018698:Glutamic Acid; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium