FIGURE 2.

Pmp22 deficiency increases myelin permeability. (A) Diagram showing the experimental setting for evaluating K⁺ permeability of sciatic nerves. Please see additional details in Materials and Methods. (B) As marked in the figure, there were 4 experimental groups. Treatment of 100mM KCl in Pmp22^+/+ mice did not significantly alter compound muscle action potential (CMAP) amplitudes, compared with Pmp22^+/+ or Pmp22^+/− mice treated with the vehicle. In contrast, treatment of 100mM KCl in Pmp22^+/− mice caused a rapid decrease of CMAP amplitudes (n = 10 Pmp22^+/+ mice, n = 11 Pmp22^+/− mice). The difference between the Pmp22^+/− K⁺ group and the other 3 groups was statistically significant (p = 0.0007). Note that within the first minute (between the 2 arrows), time points were not evenly scaled, but simply marked the points at 5, 10, 20, and 30 seconds. This was to show the rapid initial changes. (C) An experiment identical to that in B was performed to induce a reduction of CMAP by 100mM KCl (p < 0.05). However, at the 6th minute after the KCl application, KCl was washed out by Ringer’s buffer (vertical arrow in C). CMAP quickly recovered. Again, within the first 2 minutes (between the 2 horizontal arrows), time points were not evenly scaled, but simply marked the points at 0, 10, and 30 seconds. (D) A specific example was made from a Pmp22^+/+ mouse and a Pmp22^+/− mouse. CMAP remained constant in the Pmp22^+/+ mouse after KCl application (left column). In contrast, CMAP in the Pmp22^+/− mouse was decreased from pre-K⁺ 25.6 to 15.2mV after K⁺ application (arrow in the right column). The CMAP recovered to 21.0mV after the K⁺ washed out for 8 minutes. However, the 21.0mV CMAP was reduced to 17.6mV 1 minute after the second K⁺ application (arrowhead). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]