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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
Author(s) -
Lieberman Edward M.,
Pascarella Jonathan,
Brunder Donald,
Hargittai Pa'l T.
Publication year - 1990
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1990.tb08833.x
Subject(s) - ouabain , crayfish , potassium , chemistry , electrochemical gradient , extracellular , membrane potential , conductance , sodium , biophysics , analytical chemistry (journal) , membrane , biochemistry , biology , chromatography , physics , organic chemistry , fishery , condensed matter physics
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 (∼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 ∼P consumption ( Q̇ ∼ p ) of the axon. For a [K + ] o between 0.5 and 21.6 m M , Q̇∼ p averaged 52.8 ± 4.7%/h (n = 44) of the initial [ATP] + [Arg‐P]. Unlike total Q̇∼, the ouabain‐sensitive portion of Q̇∼ p was markedly influenced by [K + ] o . In 0.5 m M K + o , ouabain poisoning reduced Q̇∼ p . to 8%/h, a result indicating that 85% of the total Q̇∼ p was ouabain sensitive. For 1.35 m M K + o , the ouabain‐sensitive portion was 66%; at 5.4 m M K + o , 45%; and at 13.5 m M K + o , 41%. There was a small but significant increase in the ouabain‐sensitive Q̇∼ p at 21.6 m M K + o , compared with Q̇∼ p at 5.4 m M K + o . The pattern of effect of [K + ] o on Q̇∼ 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 ( J Na )/∼P stoichiometry of 3, an actual ratio of J Na /∼P stoichiometry of ∼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.