Molecular Aspects of Secretory Granule Exocytosis by Neurons and Endocrine Cells

Episode von Medizin - Open Access LMU - Teil 11/22 von Ludwig-Maximilians-Universität München · 1. Januar 1994

Neuronal communication and endocrine signaling are fundamental for integrating

the function of tissues and cells in the body. Hormones released by endocrine

cells are transported to the target cells through the circulation. By contrast, transmitter

release from neurons occurs at specialized intercellular junctions, the synapses.

Nevertheless, the mechanisms by which signal molecules are synthesized,

stored, and eventually secreted by neurons and endocrine cells are very similar.

Neurons and endocrine cells have in common two different types of secretory

organelles, indicating the presence of two distinct secretory pathways. The synaptic

vesicles of neurons contain excitatory or inhibitory neurotransmitters, whereas the

secretory granules (also referred to as dense core vesicles, because of their electron

dense content) are filled with neuropeptides and amines. In endocrine cells, peptide

hormones and amines predominate in secretory granules. The function and content

of vesicles, which share antigens with synaptic vesicles, are unknown for most

endocrine cells. However, in B cells of the pancreatic islet, these vesicles contain

GABA, which may be involved in intrainsular signaling.'

Exocytosis of both synaptic vesicles and secretory granules is controlled by

cytoplasmic calcium. However, the precise mechanisms of the subsequent steps,

such as docking of vesicles and fusion of their membranes with the plasma membrane,

are still incompletely understood. This contribution summarizes recent observations

that elucidate components in neurons and endocrine cells involved in

exocytosis. Emphasis is put on the intracellular aspects of the release of secretory

granules that recently have been analyzed in detail.

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