The theoretical small signal impedance of the frog node, Rana pipiens.

The small signal impedance of the frog node is calculated for frequencies from 1 Hz to 10,000 Hz and transmembrane potentials from -80 mV to -30 mV, by linearizing the voltage clamp equations of Dodge [7] and Hille [8]. The modulus of the impedance is presented for the total system, and separately for the potassium and sodium systems as a function of frequency and voltage. There is a broad resonance in the total impedance with a voltage-dependent peak frequency. At 22 degrees C, in the range -75 mV to -45 mV, the peak frequencies occur between 50 and 500 Hz. Removing the potassium system leaves a relatively sharp resonance centered around 200 Hz at -45 mV.