Summary
The current-voltage curve (I–V curve) of theChara membrane was obtained by applying a slow ramp hyper- and depolarization by use of voltage clamp. By inhibiting the electrogenic pump with 50μm DCCD (dicyclohexylcarbodiimide), theI–V curve approached a steadyI–V curve within two hours, which gave thei d -V curve of the passive diffusion channel. Thei p -V curve of the electrogenic pump channel was obtained by subtracting the latter from the former. The sigmoidali p -V curve could be simulated satisfactorily with a simple reaction kinetic model which assumes a stoichiometric ratio of 2. The emf of the pump (E p ) is given as the voltage at which the pump current changes its sign. The conductance of the pump (g p ) can be calculated as the chord conductance from thei p -V curve, which is highly voltage dependent having a peak at a definite voltage. The changes of emf and conductance during excitation were determined by use of the current clamp (I=0). Since theE p andg p (V) are known, the changes, during excitation, of emf (E d ) and conductance (g d ) of the passive diffusion channel can be calculated. The marked increase of the membrane conductance and the large depolarization during the action potential are caused by the marked increase of the conductance of the passive diffusion channel and the large depolarization of its emf. The conductance of the electrogenic pump decreases to about half at the peak of action potential, while the pump current increases almost to a saturated level.
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Kishimoto, U., Takeuchi, Y., Ohkawa, Ta. et al. A kinetic analysis of the electrogenic pump ofChara corallina: III. Pump activity during action potential. J. Membrain Biol. 86, 27–36 (1985). https://doi.org/10.1007/BF01871607
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DOI: https://doi.org/10.1007/BF01871607