The Journal of General Physiology, Vol 67, 343-367, Copyright © 1976 by The Rockefeller University Press
Electromechanical coupling in tubular muscle fibers. II. Resistance and capacitance of one transverse tubule
A Gilai
In tubular muscle fibers of the yellow scorpion the transverse tubules are
arranged in a radial symmetry. This particular morphology, enables one to
derive values for electrical components of one transverse tubule (TT) by
treating the TT as a core conductor rather than a complex network. The
electrical properties of tubular muscle fibers were completely
characterized and analyzed by measuring two independent functions of
frequency, i.e., the characteristic impedance and the propagation function.
The impedance of a single tubular muscle fiber was determined with
microelectrodes over the frequency range 1 Hz to 1.5 kHz. The results were
fitted to a possible equivalent circuit model which is based on
morphological evidence. The average component values for this model are: Ri
= 209 omega-cm, Rm, and RT = 980 omega-cm2 (referred to unit area of
surface membrane), Cm and CT = 0.9 muF/cm2, and RL = 103 omega-cm. Relating
the equivalent circuit to ultrastructure shows that the average component
values are consistent with the hypothesis that the TT is open to the
extracellular medium, the electrical capacity of surface and TT membranes
is about 1 muF/cm2, and the spread of surface depolarization into the TT is
attenuated by about 25%.
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