title: Activation of the Na pump current by external K and Cs ions in cardioballs from sheep Purkinje fibres.
abstract: The Na pump current (Ip) was measured at 30-33 degrees C as a function of the extracellular K+ or Cs+ concentrations ([K]o; [Cs]o) by means of whole cell recording from cardioballs isolated from sheep Purkinje fibres. The results show that the magnitude of Ip is an s-shaped, saturating function of [K]o or [Cs]o, respectively. Half maximal Ip activation occurs at 1.2 mM Ko or 3.2 mM Cso (clamp potential: -20 mV). These values are appreciably lower than earlier measurements on sheep Purkinje fibres indicated. The Hill coefficients for Ip activation by external K+ or Cs+ were calculated to be 1.94 and 1.73, respectively. The numbers suggest that Ip activation requires at least two external activator cations.
authors.affiliation: Department of Cell Physiology, Ruhr-University Bochum, Federal Republic of Germany.
authors.forename: H G
authors.initials: HG
authors.lastname: Glitsch
authors.forename: T
authors.initials: T
authors.lastname: Krahn
authors.forename: F
authors.initials: F
authors.lastname: Verdonck
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002586:Cesium / Q000494:pharmacology*; D004594:Electrophysiology; D006329:Heart Conduction System / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D011690:Purkinje Fibers / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012756:Sheep; D012964:Sodium / Q000378:metabolism / Q000502:physiology*
chemical_list: D002586:Cesium; D012964:Sodium; D011188:Potassium