Fig. 5.

Fatiguing HFS trains increase the CMAP of Kv1.1^V408A/+ mice. CMAP evoked from LG muscles of Kv1.1^+/+ (A) and Kv1.1^V408A/+ (B) mice and recorded before (pre) and after the delivery of HFS trains (the time at which the evoked potentials are recorded and analyzed is reported on the left hand side). (C) Plot of the integrated CMAP as a function of time elapsing from HFS train delivery and normalized to pre-fatigue value for Kv1.1^V408A/+ (filled square; n = 15) and Kv1.1^+/+ (open square; n = 15) mice. The time course of the recovery of twitch tension from fatigue is reported above the plot for direct comparison. Note that fatiguing stimulations increase remarkably the CMAP of Kv1.1^V408A/+ mice, which reached a peak 15 min after the delivery of HFS trains. Conversely, the same procedure reduced slightly the CMAP of Kv1.1^+/+ muscles. (D) Bar graph of the evoked EMG bursting activity elicited by HFS trains and integrated in either isometric or “quasi-isotonic” condition (n = 5). Note that the bursting activity in isometric condition was significantly higher than quasi-isotonic condition (***p < 0.001). (E) Integrated CMAP values were determined in either “quasi isotonic” condition, upon the delivery of HFS trains lasting 180 s (indicated as isotonic), or in isometric condition by varying the duration of HFS trains from 30 to 180 s. This procedure was used to induce different degrees of fatigue. The circles include the responses of four Kv1.1^V408A/+ mice under the conditions indicated on the right hand side. Linear regression was used to fit the data points (dashed line). Note that the integrated CMAP values increase linearly with the intensity of the stimulations.