CONICET | Buscador de Institutos y Recursos Humanos

Recently we noted that a brief depolatization resembling an action potential applied on mouse chromaffin cells in conditions of complete inhibition of Ca2+ currents (Ica) induced a moderate exocytotic process. To study more systematically this phenomenon we applied square depolarizations (-80 to +10 mV) of variable duration in presence of (i) 0 mM external Ca2+ or (ii) 5 mM Ca2+ and 100 μM Cd2+, what provoked an increase in capacitance that saturated at 17±2 y 14±1 fF respectively (~12 vescles). To buffer any possible contaminant Ca2+ that might enter to the cell or any release from internal stores we made experiments in 0 extracellular Ca2+ and 4 mM intracelular BAPTA, obtaining again a significant exocytosis (14±2 fF) in response to 100 ms depolarizations. The calcium release inhibitor 2-APB was also unable to block this exocytosis process (15±2 fF). Moreover, this Ica independent exocytosis process followed a sigmoid dependence with membrane potential, reaching the 50% of the saturating value at approximately -30 mV. When this vesicle pool was completely depleted by application of a 100 ms depolarization, it recovered with a time constant of 1.04±0.18 s. These preliminary results suggest the existence of a pool of vesicles sensitive to changes in membrane potential, which is released in absence of a measurable Ca2+ entry.