title: The activation of the sodium pump in pig red blood cells by internal and external cations.
abstract: A study has been made with pig red blood cells of the activation of the sodium pump by internal and external cations. Cell Na and K concentrations were altered using a PCMBS cation loading procedure. The procedure was characterised for resultant ionic conditions, maintenance of ATP levels and fragility. The activation of the sodium pump by external K was measured in cells suspended in choline (Na-free) solutions. External Cs was used as a substitute for K and elicited lower rates of pump activity. Both the Vmax and apparent Km for 42K influx and 134Cs influx increased as internal Na concentration was raised (within the non-saturating range). Vmax/apparent Km ratios for cation influx were constant. Raising external Cs concentration exerted a similar influence on pump activation by internal Na: both the maximum pump velocity and the apparent Na-site dissociation constant (K'Na) increased. The results provide evidence for a transmembrane connection between cation binding sites on opposite faces of the membrane and are consistent with a consecutive model for the sodium pump in pig red blood cells.
authors.forename: S C
authors.initials: SC
authors.lastname: Brand
authors.forename: R
authors.initials: R
authors.lastname: Whittam
mesh_terms: D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000097:blood; D000818:Animals; D002412:Cations; D002463:Cell Membrane Permeability / Q000187:drug effects; D002586:Cesium / Q000097:blood / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D011188:Potassium / Q000097:blood / Q000494:pharmacology*; D012964:Sodium / Q000097:blood / Q000494:pharmacology*; D013552:Swine
chemical_list: D002412:Cations; D007473:Ion Channels; D002586:Cesium; D002731:4-Chloromercuribenzenesulfonate; D000255:Adenosine Triphosphate; D012964:Sodium; D011188:Potassium