Capacity of muscle fiber membrane.

TASAKI, I. AND S. HAGIWARA. (Natl. Insts. Health, Bethesda, Md., and U. California, Los Angeles.) Capacity of muscle jiber membrane. Am. J. Physiol. 188(3): 423-429. 1957 .-Using two or three microelectrodes inserted into single muscle fibers of the toad sartorius, the electric impedance of the muscle fiber membrane was measured with a.c. between 25 and 1500 cps. It was found that the capacity of the muscle fiber membrane is practically independent of the frequency of the measuring a.c. The membrane capacity determined from the time constant of potential rise in the foot of a propagated muscle action potential agrees with the value determined by a.c. impedance measurement. It was emphasized that the a.c. method of determining the cable constants of the muscle fiber (based on eq. I under METHODS) is simple and gives satisfactory results. ECENT observations with intracellular R microelectrodes have revealed that the surface membrane of the muscle fiber of the frog or the toad has a capacity of 5-9 pf/cm2 (1-3). In the present study, we have attempted to determine whether or not this large capacity of the muscle fiber membrane varies with the frequency of the measuring a.c. We found that the membrane capacity of the muscle fiber is practically independent of the frequency in the range between 25 and 1500 cps. In addition, we have seen that the membrane capacity determined from the foot (the earliest part of the rising phase) of the action potential agrees with this large value determined by a.c.