EXOCYTOSIS AND RECOVERY OF EXOCYTOSIS AFTER ACTION POTENTIAL LIKE STIMULUS IN CHROMAFFIN CELLS: A NEW FAST RELEASABLE AND RECYCLABLE VESICLE POOL?

YANINA D. ALVAREZ; FERNANDO D. MARENGO

Huerta Grande - Córdoba

Congreso; XXVII Congreso de la Sociedad Argentina de Neurociencias; 2012

Sociedad Argentina de Neurociencias

The immediately releasable pool (IRP) is group of vesicles highly coupled to P/Q Ca2+ channels. It is expected that action potentials applied at low frequency evoke the exocytosis of vesicles from this pool. In this work we analyzed the origin of vesicles released by an action potential like stimuli (APs), and the following process or exocytosis recovery. The application of single APs induced a capacitance increase of 11±2 fF (8 vesicles). When IRP was assessed 200 ms after APs application, IRP exocytosis was decrease in a magnitude similar to APs associated exocytosis (APAE). However, while IRP was replenished with a τ=7±1s the APAE was recovered much faster (τ=1±0.1s), from similar relative values at time zero. We wonder about the mechanism of APAE recovery: it may be vesicle mobilization from IRP or recovery in situ by kiss and run. When IRP was completely depleted by a 50 ms depolarization, APAE recovered with a kinetic similar to IRP. Finally, when we inhibited endocytosis by dynasore 80 μM or nitrendipine 10 μM application, APAE recovery was not modified. We conclude that in our experimental conditions (room temperature, 5 mM Ca2+) APAE can sustain secretion at low frequencies of APs (0.2 Hz), and it would represent a vesicle pool directly fed by vesicles of IRP.