title: [Kinetic properties of sodium transport pathways in the river lamprey Lampetra fluviatilis erythrocytes].
abstract: To activate Na+/H+ exchange, intracellular pH (pHi) of erythrocytes of the river lamprey Lampetra fluviatilis were changed from 6 to 8 using nigericin. The Na+/H+ exchanger activity was estimated from the values of amiloride-sensitive components of Na+ (22Na) inflow or of H+ outflow from erythrocytes. Kinetic parameters of the carrier functioning were determined by using Hill equation. Dependence of Na+ and H+ transport on pHi value is described by hyperbolic function with the Hill coefficient value (n) close to 1. Maximal rate of ion transport was within the limits of 9-10 mmol/l cells/min, and the H+ concentration producing the exchanger 50% activation amounted to 0.6-1.0 microM. Stimulation of H+ outcome from acidified erythrocytes (pHi 5.9) with increase of H+ concentration in the incubation medium is described by Hill equation with n value of 1.6. Concentration of Na+: for the semimaximal stimulation of H+ outcome amounted to 19 mM. The obtained results indicate the presence in lamprey erythrocytes of only one binding site for H+ from the cytoplasm side and the presence of positive cooperativity in Na+ binding from the extracellular side of the Na+/H+ exchanger. Its efflux from cells in the Na+ -free medium did not change at a 10-fold increase of H+ concentration in the incubation medium. The presented data indicate differences of kinetic properties of the lamprey erythrocyte Na+/H+ exchanger and of this carrier isoforms in mammalian cells. In intact erythrocytes the dependence of the amiloride-sensitive Na+ inflow on its concentration in the medium is described by Hill equation with n 1.5. The Na+ concentration producing the 50% transport activation amounted to 39 mM and was essentially higher as compared with that in acidified erythrocytes. These data confirm the concept of the presence of two amiloride-sensitive pathways of Na+ transport in lamprey erythrocytes.
authors.forename: T I
authors.initials: TI
authors.lastname: Ivanova
authors.forename: A O
authors.initials: AO
authors.lastname: Sherstobitov
authors.forename: G P
authors.initials: GP
authors.lastname: Gusev
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000166:cytology / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D007798:Lampreys / Q000378:metabolism*; D008954:Models, Biological; D020033:Protein Isoforms / Q000378:metabolism; D026941:Sodium Channel Blockers / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D026941:Sodium Channel Blockers; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride