Involvement of Synaptic Protein Munc18 in the Process of Release of Catecholamines by Chromaffin Cells of the Rat Adrenal Gland

We studied the role of one of the synaptic proteins belonging to the SM-protein family, Munc18, in the process of exocytosis. For this purpose, we used microinjections of antibodies against protein Munc18 (anti- Munc18) into isolated chromaffin cells of the rat adrenal gland, with the aim of suppressing the function of this protein. Secretion of catecholamines was measured using carbon microelectrodes and an amperometric technique. Blocking of the function of Munc18 in the studied cells led to significant suppression of the process of secretion. In this case, the frequency of secretory events decreased, and the kinetic parameters of secretory peaks changed (their amplitude decreased, and duration of the decline phase increased). The obtained data allow us to conclude that Munc18 is one of the synaptic proteins responsible for calciumdependent exocytosis by chromaffin cells and that this protein can in a specific manner influence dimensions of the fusion pores.