Chloride channel inhibition improves neuromuscular function under conditions mimicking neuromuscular disorders.

Abstract

The skeletal muscle Cl- channels, the ClC-1 channels, stabilize the resting membrane potential and dampen muscle fibre excitability. This study explored whether ClC-1 inhibition can recover nerve-stimulated force in isolated muscle under conditions of compromised neuromuscular transmission akin to disorders of myasthenia gravis and Lambert-Eaton syndrome. Nerve-muscle preparations were isolated from rats. Preparations were exposed to pre-or post-synaptic inhibitors (ω-agatoxin, elevated extracellular Mg2+ , α-bungarotoxin or tubocurarine). The potential of ClC-1 inhibition (9-AC or reduced extracellular Cl- ) to recover nerve-stimulated force under these conditions was assessed. ClC-1 inhibition recovered force in both slow-twitch soleus and fast-twitch EDL muscles exposed to 0.2µmol/L tubocurarine or 3.5mmol/L Mg2+ . Similarly, ClC-1 inhibition recovered force in soleus muscles exposed to α-bungarotoxin or ω-agatoxin. Moreover, the concentrations of tubocurarine and Mg2+ required for reducing force to 50% rose from 0.14±0.02µmol/L and 4.2±0.2mmol/L in control muscles to 0.45±0.03µmol/L and 4.7±0.3mmol/L in muscles with 9-AC respectively (P<.05, paired T test). Inhibition of acetylcholinesterase (neostigmine) and inhibition of voltage-gated K+ channels (4-AP) relieve symptoms in myasthenia gravis and Lambert-Eaton syndrome, respectively. Neostigmine and 9-AC additively increased the tubocurarine concentration required to reduce nerve-stimulated force to 50% (0.56±0.05µmol/L with 9-AC and neostigmine) and, similarly, 4-AP and 9-AC additively increased the Mg2+ concentration required to reduce nerve-stimulated force to 50% (6.5±0.2mmol/L with 9-AC and 4-AP). This study shows that ClC-1 inhibition can improve neuromuscular function in pharmacological models of compromised neuromuscular transmission.