Functional role of second messengers on single exocytosis events

We are interested in study the ability of the second messengers, to regulate the kinetics of exocytosis by modifying the rate of neurotransmitter release from secretory vesicles.

Molecular pharmacology

The pharmacology regulation of exocytosis has importance in the context of the modification of the quantal size- amount of transmitter released. The total amount of catecholamines secreted and the kinetics of release from single vesicles can be differentially affected by drugs. This argument is the base for our work and the source of new hypothesis on the regulation and synaptic transmission efficiency.

Intravesicular factors (physic-chemicals and proteins) in the control of accumulation and catecholamine release

The vesicular pH plays a key role in the control of aggregation of vesicular solutes. The resting luminal pH of secretory granules is around 5.5, which roughly coincides with the pKa of the major vesicular protein chromogranin A. This protein plays a key role in overcoming the osmotic gradient resulting from the massive accumulation of amines within granules. We therefore proposed that the regulation of vesicular pH is, at least partially, a necessary step in the modulation of the kinetics of exocytosis and quantal size operated by some cell signals.

There are others intravesicular factors that seem to be important in the catecholamine accumulation and exocytosis. Biochemical studies had suggested that chromogranins could play an important role in the osmotic control because they bind catecholamines in high rates. The development of chromogranin A and chromogranin B knockout mice allowed us to study in vivo the role of these proteins in the accumulation and catecholamine exocytosis. We conclude that intravesicular proteins are efficient systems implicated in transmitter accumulation and in the control of neurosecretion.

Dynamic study of single secretory vesicles near of the plasma membrane Exocytosis of peptides and endocytosis of single clathrin coat pits

We are interested in study if the gradient of pH of secretory vesicles is necessary in the modulation of the kinetics of exocytosis and quantal size and might be involved in the homeostatic regulation of cytosolic Ca2+ and in two of the major functions of secretory cells, vesicle motion near of the plasma membrane and exocytosis.