THE ELECTROPHYSIOLOGY OF PLASMOLYSED CELLS OF CHARA-AUSTRALIS

The electrophysiology of non-turgid cells of Chara australis was inves tigated. The data fell into two categories. (i) 20% of cells; these we re relatively unaffected by plasmolysis (with the exception of a small depolarization) and retained many aspects of normal electrophysiologi cal behaviour, such as excitation and K+-state I/V characteristics whe n exposed to 5 mol m(-3) K+. (ii) 80% of cells; these showed electroph ysiology significantly altered by plasmolysis. These cells exhibited a large depolarization and became highly conductive after plasmolysis. The classic current relaxation kinetics upon voltage step changes dimi nished. The channels constituting this high conductance state appeared to be weakly anion selective. Application of Ca2+ channel blocker LaC l3, did not prevent development of the high conductance. Upon exposure to 5 mol m(-3) K+,the negative conductance regions were much less pro nounced than those in turgid cells. Excitation was abolished. Cells in both categories showed a steady increase in conductance with time, Th e effects of plasmolysis on cell membrane conductance were irreversibl e. The information gathered from turgorless Chara cells can be extrapo lated to explain depolarized or positive resting potentials and predom inance of weakly anion selective channels in some higher plant cell pr otoplasts.