Electrical tolerance (breakdown) of the Chara corallina plasmalemma: II. Inductive property of membrane and effects of pHo and impermeable monovalent cations on breakdown phenomenon.

Changes in the chord conductance G and the membrane electromotive force Em in the so-called breakdown region of large negative potential of the Chara plasmalemma were analyzed in more detail. In addition to the increase in G, the voltage sensitivity of the change in G increased, which was the cause of marked inductive current in the breakdown region. The break-down potential, defined as a critical potential at which both low and high slope conductances of the I-Vm relationship cross, almost coincided with the potential at which an inductive current began to appear. This breakdown potential level changed with pHo in a range between 5 and 9. The Chara plasmalemma was electrically most tolerant around pHo 7. In some cells Em shifted to a positive level as large as +50 approximately +70 mV during the breakdown phenomenon. Such a large positive shift of Em is caused mainly by the increase in conductance of Cl- and partly Ca2+ and K+.