Immediately releasable pool (IRP) exocytosis, endocytosis and vesicle replenishment in mouse chromaffin cells

FERNANDO D. MARENGO

Mar del Plata

Congreso; XXXII Congreso Anual de la Sociedad Argentina de Investigación en Neurociencias; 2017

Sociedad Argentina de Investigación en Neurociencias

IRP is a pool of vesicles selectively released by brief stimuli. Consequently it might be responsible of chromaffin cell secretion at basal action potential frequency. We previously determined that IRP exocytosis is mainly dependent on a tight coupling between its vesicles and P/Q Ca2+ channels via the synprint site of the channel. Using membrane capacitance measurements, we recently analyzed the process of exocytosis recovery after the application of an action potential like stimulus (APls). The exocytosis triggered by APls (ETAP) represents a fraction of IRP (11±2 fF), and recovered with a time constant of 0.730.11 s, what is fast enough to maintain synchronous exocytosis at 0.2-0.5 Hz stimulation. We noted that this recovery process is parcially dependent on the transference of vesicles from upstream pools. However, since we regularly observed a fast endocytosis (τ=0.71±0.21 s) after ETAP, we studied the possibility that this process might be also involved in ETAP recovery. When we inhibited fast endocytosis with dynasore, nitrendipine, an anti-dynamin monoclonal antibody, or the dynamin inhibitory peptide GST-Dyn829-842, ETAP recovery was delayed respect to the control condition. The application of the same antibody also provoked the progressive inhibition of synchronous exocytosis during low frequency APls stimulation. Therefore, we conclude that a fast dynamin-dependent endocytosis is involved in rapid ETAP recovery and in the maintenenance of exocytosis at basal APls frequencies.