Slow actions of hyperpolarization on sodium channels in the membrane of myelinated nerve

The mean sodium current, $\text{I}$, and the variance of sodium current fluctuations, var, were measured in myelinated nerve during a depolarization to $\text{V = 40}\text{mV}$ applied from the resting potential ($\text{V}{}_{\mathrm{<mtext>H</mtext>}}\text{= 0}$) or from a hyperpolarizing holding potential $\text{V}{}_{\mathrm{<mtext>H</mtext>}}\text{= ?28}\text{mV}$. From $\text{I}$ and var the relative variations in the number $\text{N}$ and the conductance γ of sodium channels following changes of the holding potential were calculated. Hyperpolarizing the membrane from $\text{V}{}_{\mathrm{<mtext>H</mtext>}}\text{= 0}$ to ?28 mV increased $\text{N}$ by a factor of 3.7, whereas γ decreased by a factor of 0.53. These actions of holding potential on sodium channels develop slowly since 500 ms prepulses to 0 or ?28 mV do not alter the values of $\text{N}$ and γ.