The Journal of Membrane Biology

, Volume 99, Issue 1, pp 41–49 | Cite as

Current-voltage relationships of potassium channels in the plasmalemma ofAcetabularia

  • A. Bertl
  • D. Gradmann


The outer membrane of mechanically prepared protoplasmic droplets fromAcetabularia mediterranea has been investigated by patch-clamp techniques. These membranes are shown to consist of physiologically intact plasmalemma. With the Cl pump inhibited, microscopic currents through K+-selective channels were studied. These currents compare well with macroscopic K+ currents as previously determined by standard microelectrode techniques and tracer flux measurements. There is about one K+ channel per μm2 in the plasmalemma. The current-voltage relationship (I−V curve) of the main open channel (channel A) is sigmoid over a voltage range between about −100 and +100 mV with saturation currents of about ±10 pA. A second species (or different state of channel A) of K+-selective channels (channel B) differs from channel A by smaller saturation currents (about ±7 pA) and a much smaller open probability. The open probability of channel A increases from almost zero at large negative voltages to about 1/2 at large positive voltages. Taking the closed times into account, the mean steady-stateI–V curve of channel A displays outward rectification about the equilibrium voltage for K+ and negative slope conductance at larger negative voltages. The open channelI–V curve of the open channels A and B, the changes of theI–V curve of the open channel A upon variation of the external K+ concentration, as well as the mean steady-stateI–V curves of channel A are described by simple reaction kinetic models, the parameters of which are determined to fit the experimental data. The results are discussed with respect to data from other K+ channels in plants and with respect to regulation of the cytoplasmic K+ concentration inAcetabularia.

Key Words

open channel voltage gating outward rectification reaction kinetic model uniport 


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Copyright information

© Springer-Verlag New York Inc. 1987

Authors and Affiliations

  • A. Bertl
    • 1
  • D. Gradmann
    • 1
  1. 1.Pflanzenphysiologisches Institut und Botanischer Garten der Universität GöttingenGöttingenFederal Republic of Germany

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