The passive electrical properties of frog skeletal muscle fibres at different sarcomere lengths.

Publisher Website
Google Scholar
Abstract
The passive electrical properties of frog skeletal muscle fibers were measured at a number of different sarcomere lengths (from 2.1 to 4.0 .mu.m). The geometrical outline of each fiber was determined from optical cross-sections and sarcomere length was measured by laser beam diffraction. When fibers were stretched to long sarcomere lengths the membrane capacity, Cm, of both normal and detubulated (glycerol-treated) fibers was significantly less than the Cm of fibers at rest length. A significant reduction in membrane conductance of fibers held at long sarcomere lengths was only seen with detubulated fibers. Membrane capacity and membrane conductance had a significant dependence on the cross-sectional area of normal fibers but were independent of cross-sectional area after detubulation. It was shown that membrane geometry depended on the sarcomere length of the fiber, and the passive membrane properties were related to sarcomere length because they depended on membrane geometry. The specific membrane capacity, calculated from the data from detubulated fibers, was 0.8 .mu.F/cm2. The internal resistivity, R1, of normal fibers, also depended on sarcomere length between 2.1 and 3.0 .mu.m. At a sarcomere length of 2.1 .mu.m the average R1 was 122 .+-. 3 .OMEGA./cm (mean .+-. SEM [standard error of mean]) and at a sarcomere length of 3.0/.mu.m the average R1 was 210 .+-. 17 .OMEGA.. cm (mean .+-. SEM). No further increase in R1 was observed with further increases in sarcomere length.