Effect of t-system luminal resistances on passive electrical properties of rat EDL muscle fibers. Experimentally determined frequency-dependent length constants (middle panels) and the propagation velocities of sinusoidal currents (right panels) were compared with theoretical predictions from three cable structures (left panels). These models either omitted (A) or included the t-system luminal resistance (B and C). The dotted lines in the circuit representations of the different cable structures indicate that the structures are of infinite length. When experimental observations from a fiber were compared with theoretical predictions from a cable structure, the model dimensions were initially adjusted to match the experimentally determined diameter, DC impedance, and the total capacitance of the particular fiber. The SEM bars for the model output, therefore, indicate the variation in the length constant and velocity that resulted from these adjustments. (A) Comparison of the experimentally determined length constant (middle) and propagation velocity of sinusoidal currents (right) with theoretical predictions from the simple cable structure, which did not include a t-system luminal resistance. (B) A similar comparison of experimental data and theoretical predictions from the lumped cable structure when its lumped t-system lumen resistance, the access resistance R_A, was set to either 10 or 20% of the DC impedance of the fiber. (C) In the distributed cable structure, the t-system was divided into 20 shells, and the t-system luminal resistance was accordingly distributed in between these shells. The experimental data has been compared with theoretical predictions when the t-system luminal resistance was varied by changing the resistivity of the t-tubular volume. Average data are shown as means ± SEM.