Spontaneous Tonic Activity Revealed in Rat Soleus Muscle by CLP290, a Novel Spinal Cord Potassium-Chloride Cotransporter Activator, during Hindlimb Suspension

The electromyographic activity of the soleus muscle is a reliableindicator of its functional status. Support unloading causes animmediate cessation of electrical activity of the soleus muscle,which resumes upon restoration of the support load. Prolonged supportunloading, however, results in the emergence of spontaneous electricalactivity of the soleus muscle. Previous research has establisheda correlation between this activity and the presence of the potassium-chloridecotransporter (KCC2) on the membranes of spinal cord motor neurons.It has also been demonstrated that the administration of the KCC2activator prochlorperazine can eliminate spontaneous soleus muscleactivity. Here, we aimed to investigate the effect of CLP290, analternative KCC2 activator, on the spontaneous tonic activity of therat soleus muscle. The results indicated that daily administrationof CLP290 to rats during a 14-day period of hindlimb suspensionprevented the reduction in KCC2 levels in lumbar spinal cord motor neuronsand the increase in soleus muscle spontaneous tonic activity. Notably,there were no significant differences in the cross-sectional areaof slow-type fibers between the antiorthostatic suspension groups withand without CLP290 administration.