Potassium channels and different states of Chara plasmalemma.

The current-voltage ( I/V) technique was employed to investigate the different electrophysiological states of the Chara plasmalemma and their interaction under a range of conditions. In K state the membrane became very permeable (conductances >20 S m 2) as [K] increased to 10 mm. As the cells were then easily damaged by the voltage-clamp procedures, it was difficult to determine the saturation K conductance. TEA (tetraethylammonium chloride) reversibly blocked the K channels, but had no effect on the I/V curve of the pump state, indicating that the K channels were not participating in this state. Acid pH (4.5) diminished the K conductance, but did not alter the response of the K channels to change in [K]. Alkaline pH (11.0) made Chara resting PD 'bistable': the PD either stayed near the estimated E and the I/V curve showed a negative conductance region typical of the K state, or it hyperpolarized and the near-linear I/V profile of the proton-permeable state was observed. [ABSTRACT FROM AUTHOR]