Abstract
This paper deals with voltage clamp experiments on the single plant cell. Nitella axillaris give membrane currents (after step changes of membrane potential) that are very similar to those of the squid giant axon except that they are much slower and smaller. For depolarizations of 20-60 my a transient inward current is followed by a steady outward current. For larger depolarizations, the steady outward current sets in during the flow of the transient inward current. The vacuolar potential at which the transient inward current does not appear, or turns to become outward, is 40-60 my positive to outside. For increasing hyperpolarizations only increasing inward currents are observed. The resistance of the membrane at rest is estimated to be 250 kΩ. cm2 for hyperpolarization and 20 kΩ. cm2 for depolarization. The minimum resistance calculated from the peak transient inward current is 4 kΩ. cm2.
An increase of outside chloride concentration to 10 mM reduces the maximum transient inward current by 40 per cent. An increase of outside calcium concentration to 10 mM, with constant Cl concentration, produces only a small decrease of the transient inward current, while the durations of the inward current and the action potential are usually increased. It is concluded that the ion responsible for the normal electrophysiological activity of the cell may be mainly chlorine ion rather than calcium ion.
