Alterations in GM taking place during sustained activity in muscle fibers affect sarcolemmal AP initiation and t-system excitation in preference to sarcolemma AP propagation. In all simulations, the distributed cable structure was used. (A) The spatial voltage profiles in steps of 100 µs of simulated electrotonic potentials similar to endplate potentials when GM in the models was modified to mimic control conditions (left), conditions during Phase I (middle), and conditions during Phase II (right). (B) A recorded AP waveform (black line, left) was used as the input function in the convolution to evaluate the passive voltage response in front of the AP. Colored lines show the initial (to 25 mV) passive sarcolemmal responses 100 and 500 µm in front of the AP. (C) The voltage responses of the sarcolemma (yellow line) 100 µm in front of the AP waveform (black line), and the voltage responses in the 20 t-system shells at this position during control (green), Phase I (red), and Phase II (blue).
