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The Journal of Membrane Biology

, Volume 62, Issue 1–2, pp 139–148 | Cite as

Current-voltage curve of electrogenic Cl pump predicts voltage-dependent Cl efflux inAcetabularia

  • H. Mummert
  • U. P. Hansen
  • D. Gradmann
Articles

Summary

The current-voltage relationship of carrier-mediated, passive and active ion transport systems with one charge-carrying pathway can exactly be described by a simple reaction kinetic model. This model consists of two carrier states (one inside, one outside) and two pairs (forwards and backwards) of rate constants: a voltage-dependent one, describing the transport of charge and a voltage-insensitive one, summarizing all the other (voltage-independent) reactions. For the electrogenic Cl pump inAcetabularia these four rate constants have been determined from electrical measurements of the current-voltage relationship of the pump (Gradmann, Hansen & Slayman, 1981;in: Electrogenic Ion Pumps, Academic Press, New York). The unidirectional Cl efflux through the pump can also be calculated by the availiable reaction kinetic parameters.36Cl efflux experiments on singleAcetabularia cells with simultaneous electrical stimulation (action potentials) and recording, demonstrate the unidirectional Cl efflux to depend on the membrane potential. After subtraction of an efflux portion which bypasses the pump, agreement is found between the measured flux-voltage relationship and the theoretical one as obtained from the reaction kinetic model and its parameters from the electrical data.

Key words

Acetabularia Cl flux current-voltage relationships electrogenic pump ion-transport model nonlinear kinetics 

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Copyright information

© Springer-Verlag New York Inc 1981

Authors and Affiliations

  • H. Mummert
    • 1
  • U. P. Hansen
    • 1
  • D. Gradmann
    • 1
  1. 1.Institut für Biologie ITübingenWest Germany

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