Highly Coupled Exocytosis in Chromaffin Cells

FERNANDO D. MARENGO

Valparaíso

Congreso; VIII Congreso Iberoamericano de Biofísica. IX Reunión Anual Sociedad Chilena de Neurociencia; 2013

Sociedad Chilena de Neurociencia

HIGHLY COUPLED EXOCYTOSIS IN CHROMAFFIN CELLS Fernando D. Marengo. Laboratorio de Fisiología y Biología Molecular. Instituto de Fisiología, Biología Molecular y Neurociencias (CONICET). Departamento de Fisiología y Biología Molecular y Celular. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Buenos Aires, Argentina. The immediately releasable pool (IRP) is a group of ready releasable vesicles rapidly released by short depolarizations. Using a pharmacological approach and KO animals for P/Q Ca2+ channels, we demonstrated in mouse chromaffin cells that the exocytosis of this pool is specifically coupled to P/Q Ca2+ current. The Ca2+ current flowing through P/Q-type Ca2+ channels is 8 times more effective to induce exocytosis in response to short stimuli than the current flowing through L-type channels. We also investigated the mechanism that may generate the coupling between IRP and P/Q-type channels. The expression of synprint (an aminoacidic sequence located in the cytosolic domain of the P/Q channel α1A subunit) reduced markedly IRP and diminished the efficiency of Ca2+ current to induce exocytosis. Finally, to evaluate the possible participation of IRP during repetitive stimulation, we studied the recovery of this pool after total depletion. The refilling rate resulted to low (7 s) to expect a significant participation of IRP at physiological stimulation frequencies. However, we found that a small fraction of IRP, which is released by an action potential like stimuli, recovers 8 times faster. These results show that IRP vesicles are specifically coupled to P/Q-type Ca2+ channels through a specific interaction at the molecular level, and they may participate of exocytosis during trains of stimuli applied at basal physiological frequencies.