013 | Synaptotagmin -7 overexpression modifies the dynamics of single exocytotic events in mice adrenal chromaffin cells

Cellular and Molecular Neurobiology

Author: Octavio Caspe | Email: octavio.caspe@uns.edu.ar

Octavio Caspe , Fernando Diego Marengo

1° Instituto de Fisiología, Biología Molecular y Neurociencias – CONICET – UBA

Synaptotagmins are major Ca2+ sensors that trigger vesicle-to-plasma-membrane fusion. Different synaptotagmin isoforms exert characteristic effects on the rate and extent of exocytosis, and modulates the content release through their effects on fusion dynamics. Although there are at least 17 Syt isoforms, chromaffin cells express only two: synaptotagmin-1 (Syt-1) and synaptotagmin-7 (Syt-7) (Proc Natl Acad Sci USA 105, 3998–4003, 2008). In this work, we analyzed the effect of Syt-1 and Syt-7 overexpression on the dynamics of dense core vesicle fusion, measured by carbon fiber amperometry, in primary cultures of mice chromaffin cells. We found that the overexpression of any of these isoforms does not affect the frequency of exocytotic events, the relative frequencies of pre-spike or stand-alone-feet, or the amount of catecholamines released from a single vesicle. However, Syt-7 does affect some parameters associated to fusion kinetics. In particular, the overexpression of Syt-7 decreased significantly the amplitude of amperometric spikes; and in addition we observed an increase tendency in the half-width, (t1/2), that reflects the duration of the individual exocytotic events, and in the spike rising time. Finally, Syt-7 reduced the duration of pre-spike and stand-alone feet, but did not affect their amplitudes. These results suggest that Syt-7 destabilizes the initial fusion pore and slows down the final fusion pore expansion.