GASTROENTEROPANCREATIC NEUROENDOCRINE TUMORS CONTAIN A COMMON SET OF SYNAPTIC VESICLE PROTEINS AND AMINO-ACID NEUROTRANSMITTERS

Human neuroendocrine tumours of the gastroenteropancreatic system contain major integral membrane proteins of small synaptic vesicles of neurons, together with characteristic membrane polypeptides of large dense-core vesicles of neurons and neuroendocrine cells. The membrane polypeptides characteristic for small synaptic and large dense-core vesicles are detected in pheochromocytomas (n=6), functional (n=6) and non-functional (n=6) foregut, and midgut carcinoids (n=17). All gastroenteropancreatic tumours contain large amounts of amino acid neurotransmitters, i.e. glycine and glutamate. Upsilon-Aminobutyric acid, however, is only found in some foregut carcinoids. Thus, neuroendocrine gastroenteropancreatic tumours possess a vesicle type with a content and membrane composition similar to small synaptic vesicles of neurons.