Figure 1.
Schematic representation of the mechanism for somatic exocytosis of serotonin in Retzius neurons. (A) Electrical activity sets in motion the transport of dense core vesicles (dcv) to the plasma membrane. In response to a train of action potentials, L-type calcium channels (LCach) open. Calcium entry activates ryanodine receptors (RyR) in the endoplasmic reticulum (er) and produces calcium-induced calcium release. The amplified calcium wave invades the soma; in the mitochondria (mit), calcium stimulates the synthesis of ATP, which activates kinesin motors (km) and vesicle transport along microtubules (mt). (B) Vesicles enter the actin cortex and myosin motors (MyM) carried by the vesicles couple to actin filaments and contribute to the transport. Release is maintained by a positive feedback loop in which the serotonin that is released activates 5-HT2 receptors (5-HT2R). Activation of phospholipase C (PLC) produces IP3 which acts on its receptors (IP3R) to activate calcium release. Such calcium maintains exocytosis going on until the last vesicles fuse (Adapted from Leon-Pinzon et al., 2014).