Figure 5.
Biphasic changes in GM during intermittent AP firing in EDL muscle fibers. Two microelectrodes impaled the same fiber of a BTS-treated muscle. One electrode was used to inject a current protocol, and the other electrode was used to measure the membrane potential. Each stimulus cycle in the experimental protocol began with a series of small square current pulses, whose resulting voltage responses could be used to obtain GM (Eq. 11). This was followed by a train of 49 larger AP-triggering pulses, after which the stimulus cycle was repeated until a total of 4,998 AP-triggering pulses had been delivered. Next, a 1-min rest period was given before a final delivery of the stimulus cycle to assess fiber recovery. (A–C) The first, 29th, and 81st of such AP trains. (D–F) Enlargements of the underlined membrane potential responses to the small current injections in the recordings of AP trains depicted above. The magnitudes of these membrane potential responses to the small currents were determined after ∼75 ms of current injection when a stable deflection was obtained (ΔVDC) and used for GM determination. (G) The average GM over such experiments (n = 5). The deflections of membrane potential in response to the small current injections in between the AP trains were also determined after 1 and 5 ms of current injection (ΔV1 and ΔV5, respectively). (H) Average observations of ΔV1, ΔV5, and ΔVDC in the experiments. Average data are presented as means with SEM.