2-APB prevents atrophic changes and alters cellular signalling during unloading of rat <i>M. Soleus</i>

IP3 receptors are found in significant quantities in muscle fibers in the sarcoplasmic reticulum, nucleus and mitochondria. We hypothesized that activation of IP3 receptors (IP3Rs) during muscle unloading may induce a weak calcium release signal, both cytosolic and nucleoplasmic, that promotes (possibly with other signaling cascades) the activation of transcription factors, leading to the expression or repression of genes involved in muscle phenotype. This hypothesis was tested by blocking IP3R during unloading of rat muscles by administering 2-APB (2-aminoethoxydiphenyl borate). Wistar rats were administered intraperitoneally at a dose of 10 mg/mg in 5 % DMSO daily. We found that the IP3R state influences the development of atrophic processes in the postural m. soleus during unloading. Administration of the IP3R blocker 2-APB to animals successfully prevented a decrease in m. soleus cross-sectional area (CSA) of both fast and slow muscle fibers. The slowdown in CSA decrease upon administration IP3R inhibitor during 7 days m. soleus unloading is associated with the prevention of a decrease in ribosomal biogenesis and an increase in the expression of autophagy markers ULK-1 and IL-6.