HISTAMINE-STORING CELLS IN THE OXYNTIC MUCOSA OF THE RAT STOMACH - A TRANSMISSION ELECTRON-MICROSCOPIC STUDY EMPLOYING FIXATION WITH CARBODIIMIDE

We studied the distribution of histamine (HA) immunoreactivity in endocrine cells of the acid-producing mucosa in rat stomach with pre-embedding immunoelectron microscopy (IEM) using an antiserum against HA. Four fixation modifications were compared to optimize the ultrastructural morphology and staining pattern with the antisera produced against carbodiimide-conjugated HA. Fixation with 4% 1-ethyl-3(3-dimethyl-aminopropyl) carbodiimide (EDCDI) combined with both 4% paraformaldehyde and 0.1% glutaraldehyde gave superior results compared with EDCDI alone. Enterochromaffin-like (ECL) cells were easily distinguished from other endocrine cells in optimally fixed samples. The peroxidase endproduct was distributed within the cytoplasm surrounding the vesicles of the ECL cells. ECL cells comprised about 75% of all endocrine cells, and about 90% of them were HA immunoreactive (HA-IR). No other HA-ER cell types were identified by EM in the basal half of the oxyntic region of rat gastric mucosa. The results suggest that a combination of EDCDI and aldehydes is suitable for IM demonstration of HA in cells. ECL cells form a predominant portion of endocrine cells in the oxyntic glands and may constitute the only significant non-mast cell store of HA in rat gastric mucosa.