D-004 | The N-terminal region of Rab3a positively regulates the opening of the early fusion pore of dense core vesicles in chromaffin cells

Cellular and Molecular Neurobiology
Author: Octavio Caspe | Email: octavio.caspe@uns.edu.ar

Octavio Caspe^1°, Fernando Diego Marengo^1°

^1° Instituto de Fisiología, Biología Molecular y Neurociencias (UBA-CONICET). Facultad de Ciencias Exactas y Naturales. Departamento de Fisiología, Biología Molecular y Celular. Universidad de Buenos Aires, Buenos Aires, Argentina

Rab3a is a small GTP binding protein associated with presynaptic and secretory vesicles that is thought to regulate positively their targeting to active zones. However, the results obtained in different cellular models were contradictory, resulting in facilitation or, alternatively, inhibition of exocytosis. To try to overcome this apparent contradiction, it was proposed that while the C-terminal fragment of Rab3a was associated to the classical effect on vesicle targeting, the N-terminal fragment was related with some type of modulation on fusion pore opening (JBC 291: 23101–23111, 2016). To study the effect of Rab3a on fusion pore regulation, we transfected the chimeric Rab3a-22a protein (N-ter-Rab3a1-80-Rab22a64-195-C-ter, J Mol Cell Biol 6(4):286-298, 2014) in primary cultures of murine chromaffin cells. This chimera loses the vesicle recruitment function, but keeps its putative capacity to modulate the fusion pore opening. We performed amperometric recordings to study the exocytosis of dense core vesicles in mouse chromaffin cells expressing the chimera. Our results show an increase in the amplitude (+20%) and a shortening of the duration (-30%) of the pre-spike-foot (PSF) in the cells expressing the chimera vs control cells, with no significant changes in spike parameters. These results suggest that the N-terminal fragment of Rab3a contributes to the opening of the early fusion pore.