The role of electrogenic pump in Chara corallina.

The conductance, G, and the electromotive force, E, of the Chara membrane were determined accurately by using the current-clamp technique. The measurements at the final steady state of inhibitor poisoning give the conductance, g1, and the electromotive force, E1, of the passive ion conducting pathways. By knowing these values the conductance, g2, and the electromotive force, E2, of the electrogenic pump can be calculated from the measured G and E at each time during the progress of inhibitor poisoning. The local closed circuit current, i, which usually causes a hyperpolarization across the passive conducting pathways, can be calculated by using g1, g2, E1 and E2 thus determined. The values of g2 and i decrease monotonically to zero with the progress of poisoning, while E2 approaches E1 asymptotically after a transient hyperpolarization. During excitation i increases markedly. Such an increased inward current through the passive conducting pathways may help in accelerating the inactivation of the excitatory mechanism.