. Ca2+ independent and voltage dependent exocytosis in mouse chromaffin cells

JOSÉ MOYA-DÍAZ; LUCAS BAYONÉS; MAURICIO MONTENEGRO; FERNANDO D. MARENGO

Padova

Congreso; Thematic Meeting sobre "Quantitative Aspects of Membrane Fusion and Fission"; 2019

Biophysical Society (USA)

I t is w idely demonstrated that the ex ocytosis of synaptic and secretory vesicles is triggered by a localiz ed Ca increase associated to theactivation of voltage dependent Ca channels. H ow ever, in neurons and neuroendocrine cells there are evidences of a different mode of fastex ocytosis, induced in response to membrane depolariz ation but lacking Ca2+ current and intracellular Ca increase. I n this w ork w einvestigated if such a mechanism can contribute to secretory vesicle ex ocytosis in mouse chromaffin cells. The application of briefdepolatiz ations on cells bathed in total absence of ex tracellular Ca induced moderate but consistent ex ocytosis, evaluated by patch-clampmembrane capacitance measurements and amperometry. This phenomenon w as also reproduced w hen the release of Ca from intracellularstores w as pharmacologically inhibited and w hen high concentrations of BAPTA w ere introduced in the cytosol. Moreover, no increase incytosolic Ca w as observed when measured w ith Fluo-8. This exocytosis process is dependent on the applied membrane potential, reachingthe 50% of the saturating value at approx imately -30 mV, and w as inhibited by the neurotox in Bont-B that specifically cleaves the SN AREprotein synaptobrevin. This Ca -independent and voltage-dependent ex ocytosis is very fast, saturating w ith a time constant < 10 ms, andrecovers completely after depletion in less than 5 s. Due to these characteristics this mechanism is able to maintain synchronous fastex ocytosis during action potential like stimuli applied at low frequencies. Finally, our data suggest that P/Q-type voltage dependent Cachannels are suitable voltage sensors coupled to the activation of this mechanism of ex ocytosis