Ionic Relations of Cells of Chara Australls X. Effects of Bicarbonate Ions on Electrical Properties

Abstract

When bicarbonate ions were added to the external medium the plasmalemma of cells of Chara australis became hyperpolarized. The potential difference (p.d.) frequently changed from -150 or -160 mV to -200 or -220 mV. An increase in membrane resistance also occurred. In the hyper-polarized state the plasmalemma was almost unresponsive to changes in potassium concentration in the medium. Dark conditions slowed or inhibited the change in p.d. due to bicarbonate. A large, reversible increase in the resistance of the plasmalemma accompanied a transition from light to dark when the membrane was hyperpolarized. Hyperpolarization was partly abolished reversibly by subsequent addition of appropriate concentrations of o-phenanthroline, monuron (l-p-chlorophenyl-3,3-dimethylurea), or hydroxylamine. It is postulated that an active "electrogenic" pump accumulates bicarbonate ions, which are accompanied by a passive flux of potassium and sodium ions. The latter flux constitutes an electric current which hyper-polarizes the plasmalemma. The active pump is dependent on energy from photosynthesis.