title: Invaginated membrane in crustacean tonic muscle fibers: estimates of membrane capacitance.
abstract: 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.
mesh_terms: D000818:Animals; D003400:Astacoidea; D004553:Electric Conductivity; D008564:Membrane Potentials; D008854:Microscopy, Electron / Q000379:methods; D009132:Muscles / Q000502:physiology* / Q000648:ultrastructure; D012508:Sarcolemma / Q000648:ultrastructure*; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure; D013499:Surface Properties