Methocarbamol blocks muscular Nav1.4 channels and decreases isometric force of mouse muscles

Background The muscle relaxant methocarbamol is widely used for the treatment of muscle spasms and pain syndromes. To elucidate molecular mechanisms of its action, we studied its influence on neuromuscular transmission, on isometric muscle force, and on voltage-gated Na+ channels. Methods Neuromuscular transmission was investigated in murine diaphragm-phrenic nerve preparations and muscle force studied on mouse soleus muscles. Na(v)1.4 channels and Na(v)1.7 channels were functionally expressed in eukaryotic cell lines. Results Methocarbamol, at 2 mM, decreased the decay of endplate currents, slowed the decay of endplate potentials and reduced tetanic force of soleus muscles. The drug reversibly inhibited current flow through muscular Na(v)1.4 channels, while neuronal Na(v)1.7 channels were unaffected. Conclusions The study provides evidence for peripheral actions of methocarbamol on skeletal muscle. Muscular Na+ channels are a molecular target of methocarbamol. Since Na(v)1.7 currents were unaffected, methocarbamol is unlikely to exert its analgesic effect by directly blocking Na(v)1.7 channels.

Automated summary

The study shows that methocarbamol exerts peripheral actions on skeletal muscle by inhibiting muscular Na+ channels, reducing muscle force. Its analgesic effect is unlikely to be achieved by directly blocking Na(v)1.7 channels.