Functional importance of synaptobrevin and SNAP-25 during exocytosis of histamine by rat gastric enterochromaffin-like cells.

Gastric enterochromaffin-like (ECL) cells release histamine upon stimulation with gastrin in a calcium-dependent manner. The intracellular mechanisms and proteins mediating exocytosis of histamine-containing vesicles in ECL cells have not been determined yet. We used immunocytochemistry to show the localization of SNAP-25 (synaptosome-associated protein of 25 kDa) and synaptobrevin VAMP (vesicle-associated membrane protein) in ECL cells of the rat gastric mucosa and in isolated, highly enriched ECL cells, which were identified with an antibody directed against the marker enzyme histidine decarboxylase. Immunoblots of isolated ECL cells demonstrated the presence of SNAP-25, synaptobrevin, synaptophysin, synaptotagmin, and syntaxin. Histamine release from isolated ECL cells permeabilized with 8 microM digitonin (2 min) was stimulated approximately 2.5-fold upon exposure to calcium (30 microM; 10-min incubation). Preincubation with 1 microM tetanus toxin light chain for 15 min attenuated calcium-induced histamine release by 40-50% and almost completely cleaved synaptobrevin. Botulinum neurotoxin A (100 nM) totally blocked calcium-induced histamine release and cleaved SNAP-25. We conclude that synaptobrevin, synaptophysin, synaptotagmin, SNAP-25, and syntaxin are present in gastric ECL cells. Inhibition of histamine secretion by clostridial neurotoxins associated with the cleavage of synaptobrevin and SNAP-25 implicates the functional importance of these proteins in the docking and fusion of histamine vesicles.