Study of the Mechanism of Gamma-Aminobutyric Acid Inhibitory Effect on the Myotube Formation in Cell Culture

Gamma-aminobutyric acid (GABA) is commonly considered as a signaling molecule in the synapses of the central nervous system, where it plays the role of the main inhibitory neurotransmitter in the mature brain and participates in the process of neurogenesis. Recently, data have been obtained indicating that GABA may also be involved in the early stages of skeletal muscle tissue development. In the present study, performed on rat myocyte culture, the effect of exogenous GABA on the process of fusion of myocytes into myotubes was investigated by analyzing such a morphometric indicator as the "fusion index". The addition of the amino acid to the culture led to a significant concentration-dependent inhibition (up to a complete cessation) of the formation of myotubes. GABAA receptors and GABA transporters (GAT-2) were considered among possible proteins capable of mediating the effect of amino acids. Evidence of the presence of these proteins on cultured cells was obtained using immunohistochemical methods. The blockade of GABA receptors by gabazine did not affect the fusion index in any way, and GABA continued to exert inhibitory effect in its presence. Inhibition of GABA transporters by nipecotic acid reduced the myocyte fusion index; however, the GABA effect was no longer present under the action of the transporter blocker. The data obtained are consistent with the hypothesis about the participation of the amino acid GABA at the early stages of skeletal muscle development; it suggests that the inhibitory effect of the exogenous amino acid may be due to an increase in its concentration in the sarcoplasm, since both the addition of a GABA transporter blocker and an increase in the extracellular concentration of GABA negatively affect the formation of myotubes.