The Journal of General Physiology, Vol 66, 133-138, Copyright © 1975 by The Rockefeller University Press
Resistivity of axoplasm. I. Resistivity of extruded squid axoplasm
KS Cole
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.
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