ACTION POTENTIAL OF NITELLA INTERNODES

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Abstract
The ionic current during a non-propagating action potential is analysed from the voltage clamp experiments. The shape of the action potential of the Nitella internode can be reconstructed from the data of the voltage clamp experiments. The N-shaped current-voltage characteristics (I-V curve) of the Nitella membrane is not constant with time as it is in the tunnel diode, but decays with time, converging finally into a delayed rectification curve. The temporal locus of the potential at which each I-V curve crosses the voltage axis coincides almost exactly with the action potential. The membrane resistance which is calculated from the slope of the I-V curve at each intersection with the voltage axis also changes in parallel to the action potential. Such correlations are found in the Nitella not only in the pond water, but also in high Na, high Ca or high Mg medium, where the shape of the action potential is modified in various ways. It is highly probable that the action potential is a locus of the change of the membrane potential so that the net membrane current may be maintained at zero after the transient modification of the membrane structure by stimulation.

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