Transient translocation of N-type calcium channels from secretory granules to the cell surface

The involvement of actin, calcium channels and exocytosis proteins in somato-dendritic oxytocin and vasopressin release

Hypothalamic magnocellular neurons release vasopressin and oxytocin not only from their axon terminals into the blood, but also from their somata and dendrites into the extracellular space of the brain, and this can be regulated independently. Differential release of neurotransmitters from different compartments of a single neuron requires subtle regulatory mechanisms. Somato-dendritic, but not axon terminal release can be modulated by changes in intracellular calcium concentration [(Ca²⁺)] by release of calcium from intracellular stores, resulting in priming of dendritic pools for activity-dependent release. This review focuses on our current understanding of the mechanisms of priming and the roles of actin remodeling, voltage-operated calcium channels (VOCCs) and SNARE proteins in the regulation somato-dendritic and axon terminal peptide release.

Stimulus-dependent translocation of kappa opioid receptors to the plasma membrane

We examined the cellular and subcellular distribution of the cloned kappa opioid receptor (KOR1) and its trafficking to the presynaptic plasma membrane in vasopressin magnocellular neurosecretory neurons. We used immunohistochemistry to show that KOR1 immunoreactivity (IR) colocalized with vasopressin-containing cell bodies, axons, and axon terminals within the posterior pituitary. Ultrastructural analysis revealed that a major fraction of KOR1-IR was associated with the membrane of peptide-containing large secretory vesicles. KOR1-IR was rarely associated with the plasma membrane in unstimulated nerve terminals within the posterior pituitary. A physiological stimulus (salt-loading) that elicits vasopressin release also caused KOR1-IR to translocate from these vesicles to the plasma membrane. After stimulation, there was a significant decrease in KOR1-IR associated with peptide-containing vesicles and a significant increase in KOR1-IR associated with the plasma membrane. This stimulus-dependent translocation of receptors to the presynaptic plasma membrane provides a novel mechanism for regulation of transmitter release.