gamma-Aminobutyric acid secretion from pancreatic neuroendocrine cells.
OBJECTIVE
Neuroendocrine cells and tumors derived therefrom contain hormone-storing large dense core vesicles and neuron-like small synaptic vesicle analogues with unknown function. The aim of this study was to characterize the small synaptic vesicle pathway in detail.


METHODS
In human pancreatic neuroendocrine tumors and corresponding mammalian cell lines, the expression of key proteins if regulated secretion were detected by immunofluorescence microscopy. Using 3H-gamma-aminobutyric acid (GABA), uptake and release by small synaptic vesicle analogues were studied.


RESULTS
Tumor tissues obtained from 14 patients expressed key proteins of neurosecretion such as synaptobrevin, syntaxins, and SNAP 25. These proteins were also found in the cell lines AR42J, BON, RIN, and INR. The cell lines specifically transported GABA by low-affinity plasma membrane transporter and showed an adenosine triphosphate-sensitive GABA uptake into an intracellular compartment. Stored GABA was released upon stimulation by regulated exocytosis. Electrophysiological analyses suggested that calcium-dependent secretion was mediated by activation of voltage-dependent calcium channels of mainly the L type, but also of the N and probably the T type.


CONCLUSIONS
Small synaptic vesicle analogues in neuroendocrine cells and tumors can store and secrete GABA and probably other amino acid transmitters by regulated exocytosis comparable with neurons.
Anhert-Hilger
G
G
Medizinische Klinik und Poliklinik, Abteilung Innere Medizin mit Schwerpunkt Gastroenterologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Germany.
Stadtbäumer
A
A
Strübing
C
C
Scherübl
H
H
Schultz
G
G
Riecken
E O
EO
Wiedenmann
B
B
D000328:Adult; D015220:Calcium Channels / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D018358:Neuroendocrine Tumors / Q000378:metabolism*; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D013572:Synaptic Vesicles / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25; D014407:Tumor Cells, Cultured / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D015220:Calcium Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; C494208:SNAP25 protein, human; D050825:Synaptosomal-Associated Protein 25; D005680:gamma-Aminobutyric Acid