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Voltage noise, current noise and impedance in space clamped squid giant axon


The relationship between voltage noise at constant current and current noise at constant voltage across a linear electrical system is emphasized. In systems like the nerve membrane near its resting state, which show a complicated dependence of impedance on frequency in the range 1–1000 hertz, current noise and voltage noise are completely different. Two different preparations of the axon at rest are used, resulting in small area (∼ 0.04 cm2) and large area (∼ 0.4 cm2) membranes, and in different intracellular compositions. These are shown to give the same results when membrane impedance is accounted for. A distinct hump exists in the voltage spectrum, which is absent in the current spectrum. This structure depends on temperature and voltage, and may be understood when membrane impedance is taken into account. This result is in contrast with previously published work of voltage noise from squid axon. It is argued here that voltageclamp/current-noise data is most likely to give significant kinetic information about conductance changes in membranes.

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Supported by the CNR and the NSF.

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Wanke, E., DeFelice, L.J. & Conti, F. Voltage noise, current noise and impedance in space clamped squid giant axon. Pflugers Arch. 347, 63–74 (1974).

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Key words

  • Current Noise
  • Voltage Noise
  • Impedance
  • Squid Axon