Figure 6.

Contractile properties of fast and slow skeletal muscle in Kv3.1-deficient mice. (A) Soleus (a and b) and EDL muscles (c and d) from Kv3.1^+/+, Kv3.1^+/−, and Kv3.1^−/− mice were subjected to isometric contractions induced by electrical stimulation at either 10 Hz (a and c) or 40 Hz (b and d). Muscle relaxation was slower and mechanical summation occurred at lower frequencies in Kv3.1^−/− compared with Kv3.1^+/− or Kv3.1^+/+ muscles. (B) Time-to-peak-force (TPF) and half-relaxation time (½RT) was measured for single twitches. One-way ANOVA tests followed by Tukey’s multiple comparison tests revealed significant differences for Kv3.1^−/− muscles (mean ± SE; n = 7–10 muscles; ∗, P < 0.05; ∗∗, P < 0.01; ∗∗∗, P < 0.001). (C) The forces for a single twitch and for a tetanus were measured for soleus and EDL of wild-type, heterozygous, and homozygous Kv3.1 mice. Both types of skeletal muscles of Kv3.1^−/− mutants produced smaller forces than the corresponding muscles from heterozygous or wild-type mice [mean ± SE; n = 7–11 muscles; ∗, P < 0.05; ∗∗, P < 0.01 (Tukey test); P < 0.05 in one-way ANOVA].