Intracellular chloride and potassium ions in relation to excitability ofChara membrane

Abstract

Summary. Internodal cells of Chara australis were made tonoplast-free by replacing the cell sap with EGTA-containing media; then the involvement of internal C1 and K + in the excitation of the plasmalemma was studied.[C1-]i was drastically decreased by perfusing the cell interior twice with a medium lacking C1 . The lowered [C1-]i was about 0.01 raM. Cells with this low [C1-]~ generated action potential and showed an N-shaped V-I curve under voltage clamped depolarization like C1--rich cells containing 13 or 29 mM C1-. Em at the peak of the action potential was constant at [C1-]i between 0.01 and 29 m~a. The possibility that the plasmalemma becomes as permeable to other anions as to C1-during excitation is discussed.At [C1 ]~ higher than 48 raM, cells were inexcitable. When anions were added to the perfusion medium to bring the K + concentration to 100 raM, NO~, F-, SO 2-, acetate, and propionate inhibited the generation of action potentials like CI-, while methane sulfonate, PIPES, and phosphate did not inhibit excitability.The duration of the action potential depended strongly on the intracellular K + concentration. It decreased as [K+]i (K-methane sulfonate) increased. Increase in [Na+]~ (Na-methane sulfonate) also caused its decrease, although this effect was weaker than that of K +. The action of these monovalent cations on the duration of the action potential is the opposite of their action on the membrane from the outside (cf Shimmen, Kikuyama & Tazawa, 1976, J. Membrane Biol. 30: 249).In Characeae cells, permeability of the plasmalemma to C1-increases enormously upon excitation (Gaffey

Simultaneous Measurements of Cytoplasmic K+ Concentration and the Plasma Membrane Electrical Parameters in Single Membrane Samples of Chara corallina

“…2b, 6) and insensitive to tetraethylammonium chloride, a K'-channel antagonist which blocks the Chara K' state. These facts support the view that the K' channels are closed in low K,' (4,24). The membrane conductance is distributed between the proton pump and a relatively K'-insensitive leak pathway across the membrane.…”

Plasmalemmal, voltage-dependent ionic currents from excitable pulvinar motor cells ofMimosa pudica

“…However, due to the low frequency of these events, it is not possible to make any real correlation with this particular internal solution. Nevertheless, certain characteristics of this solution may be favorable for action potential generation, as found in perfused tonoplast-free cells of Chara australis where low internal C1 concentrations (<30 mM) were required for excitability (Shimmen & Tazawa, 1980). Measured values of internal C1 in Characea are between 10-30 mM (Tazawa, Kishimoto & Kikuyama, 1974).…”

A Tight-Seal Whole Cell Study of the Voltage-Dependent Gating Mechanism of K+-Channels of Protoplasmic Droplets of Chara corallina

“…Many authors have published data showing that K+-channels are involved in the excitation process of plant cells (e.g. 8,19,26,27), and that potassium ions are the main species transported in the leakage current (2). K+-channels also play a role in the light-induced membrane potential change in perfused Chara corallina cells (30) and in Eremosphaera viridis (17).…”