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Thermodynamic analysis of active sodium transport and oxidative metabolism in toad urinary bladder

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Summary

Measurements of electrical current and oxygen consumption were carried out concurrently under voltage clamp conditions in 11 toad hemibladders. Inhibition of active transport with amiloride then permitted evaluation of the passive conductance and the rate of basal oxygen consumptionJ br , allowing the simultaneous determination of the rates of active sodium transportJ aNa and suprabasal, oxygen consumptionJ sbr .J aNa andJ sbr were linear functions of the electrical potential difference over a range of ±80 mV. This allowed the comprehensive application of a linear nonequilibrium thermodynamic formalism, leading to the evaluation of the affinityA (negative free energy) of the metabolic reaction driving transport, all phenomenological coefficients, and the degree of couplingq relating transport to metabolism. Values ofA determined by two techniques wereA 1=56.0±5.8 andA 2=58.2±6.5 kcal per mole. Values ofq determined by two techniques agreed well and were less than 1, indicating incompleteness of coupling, and hence lack of fixed stoichiometry between Na transport and O2 consumption. The affinity and the electromotive force of sodium transportE Na are not closely correlated, reflecting the fact thatE Na comprises both kinetic and energetic factors.

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Abbreviations

A :

affinity of metabolic reaction (kcal· mole−1)

E Na :

electromotive force of sodium transport (mV) (=(Δψ) aJNa=0 )

F :

Faraday's constant (kcal·mV−1·Equiv−1)

I :

electrical current (μA·cm−2)

J aNa :

rate of active sodium transport (pmoles·cm−2·S−1)

J r :

rate of oxygen consumption (pmoles·cm−2·s−1)

J sbr :

rate of suprabasal oxygen consumption (pmoles·cm−2·s−1)

J br :

rate of basal oxygen consumption (pmoles·cm−2·s−1)

\(\left. \begin{array}{l} L_{Na} \\ L_{Na,r} \\ L_r \\ \end{array} \right\}\) :

phenomenological coefficients (μmoles2·cm−2·s−1·kcal−1)

q :

degree of couplingL Na,r/(L Na L r)1/2 relating active transport and metabolism

κ:

total conductance (mmho·cm−2)

K a :

active conductance (mmho·cm−2)

K p :

passive conductance (mmho·cm−2)

Δψ:

potential difference (ψ serosal-ψ mucosal) (mV) The subscript zero indicates measurements made at ΔΨ=0

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Authors and Affiliations

  1. Department of Physiology, Boston University School of Medicine, Boston, Massachusetts

    Michael A. Lang, S. Roy Caplan & A. Essig

  2. Department of Membrane Research, Weizmann Institute of Science, Rehovot, Israel

    Michael A. Lang, S. Roy Caplan & A. Essig

Authors
  1. Michael A. Lang
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  2. S. Roy Caplan
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  3. A. Essig
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Lang, M.A., Caplan, S.R. & Essig, A. Thermodynamic analysis of active sodium transport and oxidative metabolism in toad urinary bladder. J. Membrain Biol. 31, 19–29 (1977). https://doi.org/10.1007/BF01869397

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  • DOI: https://doi.org/10.1007/BF01869397

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