Complex admittance of Na+ conduction in squid axon.

The complex admittance, Y(p), of squid axon was measured (4--1000 Hz) during step voltage clamp to obtain linear data on Na+ conduction. Y(p) is used as a spectroscopic tool to identify Na+ and K+ conduction, which dominate Y(p) at low frequencies and can be separated from each other and from the static capacitance. Na+ conduction is readily distinguishable from K+ conduction in that it produces a steady-state negative conductance. The admittance of the Na+ system can show an anomalous resonance or an antiresonance depending on whether the net shunt conductance is negative or positive. Use of the Na+ negative conductance to neutralize leakage yields a measurement of dielectric capacitance at low frequency. A 90 degrees phase angle suggests that the capacitance is ideal.