Effect of Chloride Channel Inhibition in Muscle with Reduced Neuromuscular Transmission

Abstract

Recently, we demonstrated that ClC-1 chloride channels are acutely inhibited in active muscle. Since such ClC-1 channel inhibition enhances muscle excitability it can be envisaged that this regulation protects against loss of muscle excitability and fatigue in active muscle. However, it is not known whether ClC-1 channel inhibition specifically affects neuromuscular transmission. PURPOSE: The aim of this study was to evaluate the role of ClC-1 channels for neuromuscular transmission. METHODS: To do this we determined the effect of inhibiting ClC-1 on the function of rat muscle in which the neuromuscular transmission was partially blocked with tubocurarine. RESULTS: Fig. 1 presents recordings of muscle force and electrical activity (M-waves) from such an experiment. The left panel shows traces of tetanic force and M-waves under control conditions. Addition of tubocurarine (middle panel) caused a 42% loss of maximal force compared to control, and an intense decline in force within a single tetanus (fade). With subsequent ClC-1 channel inhibition, the maximal force was restored to 73% of control force and the fade was greatly reduced (right panel). The depressing effect of tubocurarine and the subsequent recovery of muscle function with ClC-1 inhibition were both mirrored by corresponding M-wave changes. Similar observations were done in 5 muscles. CONCLUSION: We conclude that ClC-1 channel inhibition in active muscle could enhance neuromuscular transmission during exercise. In addition, a number of muscle disorders are associated with malfunctioning neuromuscular transmission and our observations implicate ClC-1 channels as a possible drug target in future treatment of such disorders.Fig. 1: Inhibition of ClC-1 chloride channel recovers tetanic force in muscles with compromised neuromuscular transmission. Tetanic force and M-wave recordings from experiment where a rat muscle was stimulated to contract using pulses of 0.02 ms duration and 10 V, applied at 60 Hz for 1 s to the nerve via a suction electrode. The recordings were initially obtained in control buffer (left panel), then after 1 hr with 0.25 μM tubocurarine (middle panel) and finally 1 hr after addition of 10 μM 9-AC to the tubocurarine treated muscle (right panel). The M-waves were used to assess the excitability of the muscle. M-waves indicated by black triangles have been enlarged.