The electrical resistivity of cytoplasm

Area of Science:

• Neuroscience
• Cell Biology
• Biophysics

Background:

• Accurate measurement of cytoplasmic resistivity is crucial for understanding cellular electrophysiology.
• Previous microelectrode techniques were limited by electrode polarization artifacts.

Purpose of the Study:

• To measure the intrinsic cytoplasmic resistivity of Aplysia giant neurons and barnacle muscle fibers.
• To refine a single microelectrode technique to overcome electrode polarization.

Main Methods:

• A single metal microelectrode was inserted into giant cells (Aplysia neurons, barnacle muscle).
• Complex impedance was measured across a frequency range (500 kHz–5.7 MHz).
• Data were extrapolated to infinite frequency on the complex Z plane to eliminate polarization effects.

Main Results:

• Extrapolated cytoplasmic resistivities were 40 omega-cm for Aplysia neurons and 74 omega-cm for barnacle muscle.
• Barnacle data align with previous sarcoplasmic resistivity measurements.
• Aplysia neuron data suggest intracellular membranes cause electrode polarization artifacts at lower frequencies.

Conclusions:

• The refined microelectrode technique provides accurate cytoplasmic resistivity values.
• Intracellular membranes can artifactually increase apparent resistivity by reducing electrode surface area.
• This study clarifies potential artifacts in electrophysiological measurements of cell resistivity.