RAPID RECOVERY OF EXOCYTOSIS AFTER ACTION POTENTIAL-LIKE STIMULATION IN MOUSE CHROMAFFIN CELLS IS COUPLED TO A FAST ENDOCYTOTIC PROCESS

JOSÉ MOYA-DÍAZ; YANINA ÁLVAREZ; MAURICIO MONTENEGRO; ANA VERÓNICA BELINGHERI; FERNANDO D. MARENGO

Cairns

Congreso; 18th International Symposium of Chromaffin Cell Biology; 2015

International Symposium of Chromaffin Cell Biology

The immediately releasable pool (IRP) is a group of vesicles that is selectively released by short length stimuli, and consequently might be responsible of chromaffin cell secretion at basal action potential frequency. However, the process of replenishment after IRP depression is too slow (τ=7.5±1.1 s) to allow a sustainable exocytosis even at low frequencies. Using membrane capacitance measurements on mouse chromaffin cells, we 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 investigated the possible mechanisms involved in rapid ETAP recovery. First, we found that the depletion of the ready releasable pool (RRP) significantly delayed the recovery of ETAP. Since we regularly observed a fast endocytosis (τ=0.71±0.21 s) after ETAP, we also studied the possibility that this process might be involved in ETAP recovery. When we inhibited fast endocytosis with dynasore, nitrendipine, or using an anti-dynamin monoclonal antibody, 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 vesicle mobilization from RRP and fast endocytosis are both involved in rapid ETAP recovery.