AJP - Cell Physiology, Vol 235, Issue 5 220-C226, Copyright © 1978 by American Physiological Society
Invaginated membrane in crustacean tonic muscle fibers: estimates of membrane capacitance
K. L. Rossner and R. G. Sherman
Surface and volume densities of the invaginated membrane components of
tonic muscle fibers of crayfish (Orconectes rusticus) were determined by
stereological methods. Surface densities of the sarcolemma, sarcolemmal
invaginations, T tubules and Z tubules were 2.0, 5.9, 26.3, and 3.3
micron2/100 micron3 of fiber, respectively, and volume densities of the
sarcolemmal invaginations, T tubules, and Z tubules were 0.28, 0.29, and
0.08 micron3/100 micron3. The values obtained for surface density show that
95% of the membrane exposed to the extracellular environment is composed of
invaginated membrane. Specific membrane capacitance, determined from
square-wave pulse analysis and referred to the apparent area of surface
sarcolemma, was 30.3 muF/cm2. However, after correction for the extent of
invaginated membrane, the specific membrane capacitance was 1.6 muF/cm2.
