IDENTIFICATION OF SYNAPTIC PROTEINS AND THEIR ISOFORM MESSENGER-RNAS IN COMPARTMENTS OF PANCREATIC ENDOCRINE-CELLS

Several proteins that are of importance for membrane trafficking in th e nerve terminal have recently been characterized. We have used Wester n blot and immunohistochemistry to show that synaptotagmin, synaptobre vin/VAMP (vesicle-associated membrane protein), SNAP-25 (synaptosomal- associated protein of 25 kDa), and syntaxin proteins are present in ce lls of the islets of Langerhans in the endocrine pancreas. Synaptotagm in-like immunoreactivity (-LI) was localized to granules within the cy toplasm of a few endocrine cells located in the periphery of the islet s, identified as somatostatin-containing cells, and in many nerve fibe rs within the islets. VAMP-LI was seen in granules of virtually all pa ncreatic islet cells and also in nerve fibers. SNAP-W LI and syntaxin- LI were predominantly present in the plasma membrane of the endocrine cells, including insulin-producing beta cells. In situ hybridization, using isoform-specific oligonucleotide probes, detected VAMP-2, cellub revin, SNAP-25, syntaxin 1A, 4, and 5, and munc-18 mRNAs in isolated p ancreatic islets and in insulin-producing cells. The results show the presence of several synaptic proteins at protein and mRNA levels in pa ncreatic islet cells, suggesting that they may have specific roles in the molecular regulation of exocytosis also in insulin-secreting cells .