Electrical tolerance of the Chara corallina plasmalemma.

[Ca2+]o controls at least three distinct electrical phenomena in the Chara plasmalemma. 1). Increase of the electrical tolerance. 2). Decrease of the G without a marked change of the Gp/Gd ratio. 3). Elevation of the threshold for excitation (data not shown). On the other hand, [Mg2+]o shows quite opposite effects. Thus, optimum [Ca2+]o and [Mg2+]o are expected in vivo. Voltage dependencies of various conductances in the Chara plasmalemma are schematically shown in Fig. 4.