Resistivity of axoplasm. I. Resistivity of extruded squid axoplasm

Six methods have given squid axoplasm resistivities of from 1.0 to 6.9 times seawater (X SW), so another was tried. A 100-mum platinized electrode was to be inserted from each end of an axion in iso-osmotic sucrose and impedance between them measured vs. separation. But observations that the resistance of axons in sucrose increased steadily ruled this out. Axoplasm from two or three axons was transferred to a glass capillary, 0.6 mm ID, and the 1-kHz series resistance and reactance were measured at electrode separations from 16 to 2 mm. The resistance was linear vs. distance, giving the resistivity, while the reactance was nearly constant, implying constant electrode contributions. Frequency runs from 10 Hz to 30 kHz at 10 mm gave electrode impedances of the form (jomega)-alpha, allowing 1-2% effects on the axoplasm resistivities. In nine experiments, one was discarded for cause, the range and average resistivities were, respectively, 1.2- 1.6 and 1.4 times those of artificial seawater (19.7 omegacm at 24.4 degrees C). No single cause for the variability was apparent. These experiments essentially confirm the means and variations of two early experiments with intact axons and recent results with a single internal electrode to give overall resistivities of 1.4 +/- 0.2 X SW.