title: Effect of extracellular potassium on ouabain-sensitive consumption of high-energy phosphate by crayfish giant axons: a study of the energy requirement for transport in the steady state.
abstract: Crayfish axons exposed to a high or low extracellular K+ concentration ([K+]o) maintain intracellular Na+ and K+ concentrations constant, for up to 3 h, by adjusting both the Na+/K+ transport "coupling ratio" and turnover rate in compensation for changes in ion fluxes due to altered electrochemical gradients. These findings give rise to the prediction that the steady-state consumption of high-energy phosphate (approximately P) [ATP and phospho-L-arginine (Arg-P)] is inversely proportional to the [K+]o, i.e., directly proportional to the product of membrane conductance and magnitude of the transmembrane electrochemical gradients for Na+ and K+. This investigation was designed to test this hypothesis. The [K+]o did not influence total approximately P consumption (Q approximately P) of the axon. For a [K+]o between 0.5 and 21.6 mM, Q approximately P averaged 52.8 +/- 4.7%/h (n = 44) of the initial [ATP] + [Arg-P]. Unlike total Q approximately P, the ouabain-sensitive portion of Q approximately P was markedly influenced by [K+]o. In 0.5 mM K+o, ouabain poisoning reduced Q approximately P to 8%/h, a result indicating that 85% of the total Q approximately P was ouabain sensitive. For 1.35 mM K+o, the ouabain-sensitive portion was 66%; at 5.4 mM K+o, 45%; and at 13.5 mM K+o, 41%. There was a small but significant increase in the ouabain-sensitive Q approximately P at 21.6 mM K+o, compared with Q approximately P at 5.4 mM K+o. The pattern of effect of [K+]o on Q approximately P was similar to its effect on the electrical power content of the Na+ and K+ electrochemical gradients. In contrast to the generally accepted Na+ flux (JNa)/approximately P stoichiometry of 3, an actual ratio of JNa/approximately P stoichiometry of approximately 33:1 was calculated for the experiments reported here, a result suggesting that cells in a zero-membrane current steady state utilize efficient energy conservation mechanisms that may not operate under non-steady-state conditions.
authors.affiliation: Department of Physiology, School of Medicine, East Carolina University, Greenville, NC 27834-4354.
authors.forename: E M
authors.initials: EM
authors.lastname: Lieberman
authors.forename: J
authors.initials: J
authors.lastname: Pascarella
authors.forename: D
authors.initials: D
authors.lastname: Brunder
authors.forename: P T
authors.initials: PT
authors.lastname: Hargittai
mesh_terms: D000227:Adenine Nucleotides / Q000096:biosynthesis; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000378:metabolism; D003400:Astacoidea; D001369:Axons / Q000378:metabolism*; D001692:Biological Transport; D004734:Energy Metabolism / Q000187:drug effects*; D005110:Extracellular Space / Q000378:metabolism*; D006706:Homeostasis; D009943:Organophosphorus Compounds / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*
chemical_list: D000227:Adenine Nucleotides; D009943:Organophosphorus Compounds; D010710:Phosphates; C015441:phospho-L-arginine; D010758:Phosphorus; D010042:Ouabain; D000255:Adenosine Triphosphate; D001120:Arginine; D011188:Potassium