Abstract. The receptors in the fundic mucosa that mediate gastrin stimulation of acid secretion have been studied. Synthetic human gastrin-17-I (G17) with a leucine substitution in the 15th position ([Leu'5]

We have developed a model to allow study of the release of somatostatinlike immunoreactivity (SLI) from gastric mucosal cells. Collagenase-dispersed canine fundic mucosal cells were separated by counterflow elutriation. SLI-containing cells were identified in the fractions with small cells (9-11 microns), and these fractions were plated onto collagen. After 2 days in culture, SLI content of the cells was maintained; SLI-positive cells, detected by peroxidase-antiperoxidase immunohistochemistry, comprised 70 +/- 6% (mean +/- SE, n = 6) of these cultured cells. Release of SLI from these cultures into the medium was determined by radioimmunoassay. Epinephrine, dibutyryl cAMP, and gastrin each stimulated SLI release in a time-dependent manner, with a steady rate of secretion maintained for 120 min of incubation. Both epinephrine and dibutyryl cAMP markedly potentiated the release of SLI stimulated by gastrin but were not themselves mutually potentiating. Upon Sephadex G-50 column chromatography of incubation medium and extracts of cultured cells, SLI eluted primarily in a single peak that cochromatographed with synthetic somatostatin tetradecapeptide. Our data suggest that gastrin and adrenergic stimuli act directly on canine fundic somatostatin cells and that potentiating interactions between secretagogues may be important modulating elements in somatostatin cell secretory function.

To develop techniques for studying transport properties and secretory function of selected cell types in the gastric mucosa, separated fractions of dispersed canine fundic mucosal cells were placed in short-term culture to form epithelial monolayers. Cell fractions enriched in either chief, parietal, or mucous cells were prepared by using counterflow centrifugation and were plated on type I collagen. An epithelial monolayer formed by ==36 hr. Immunofluorescence with an antipepsinogen I antibody revealed pepsinogen-containing granules in >95% of the cells, regardless ofwhether the monolayers were formed from the mucous, chief, or parietal cell-enriched fractions. Upon achieving confluency, chief cell monolayers were mounted in Ussing chambers to study their electrical properties. Under basal conditions, monolayers (n = 6) had a spontaneous potential difference (PD) (±SEM) of 26 ± 4 mV (apical surface negative), a short-circuit current (Isc) (±SEM) of 16 ± 2 ,LA/cm2, and a transepithelial resistance (R) (± SEM) of 1,480 -210 fl-cm2 Histamine increased the short-circuit current, an effect blocked by an H2-receptor antagonist. Seventy percent of the spontaneous PD was amiloride sensitive, suggesting sodium absorption accounted for a major component of the PD. These preparative techniques yield highly enriched chiefcell monolayers, which maintain morphological and functional cellular differentiation for >48 hr in culture, thus allowing study oforiented functions ofa selected cell type. The present studies indicate that an H2 receptor enhances electrogenic ion transport in chief cell monolayers, indicating that histamine can act on fundic mucosal cells other than just parietal cells.The characterization of transport properties of selected cell types in tissues with heterogeneous cell populations such as the gastric mucosa is ofgreat interest to epithelial physiologists. The gastric mucosa has two types of mucous cells-surface mucous cells that line the lumen of the stomach and mucous neck cells that occupy the upper portion of the gastric glands. The gastric glands, found in the fundic region ofthe stomach, are composed primarily of the acid-secreting parietal cells and the chief cells, which secrete the acid protease pepsin. Elucidation of the role ofspecific cell types in the varied functions ofthe gastric mucosa has proven to be a difficult problem. The difficulty has been encountered not only because of the cellular heterogeneity of the mucosa but also because the regulatory pathways that modulate cell function are quite complex, with many ofthe chemical transmitters involved present within the mucosa itself. Thus, the cellular mechanisms regulating ion transport, the secretory function ofparietal, chief, mucous, and endocrine cells, and the mechanisms involved in gastric mucosal defense against ulcer formation have not been clarified in studies with intact mucosa.Tissue dispersion and cell separation techniques (1, 2) circumvent some of the problems that result from the heterogeneity of cell types and th...

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Endogenous prostaglandins (PGs) influence resistance of the gastric mucosa to injury, but the source of PGs is unknown. Using radioimmunoassay, we studied PG production by dispersed canine fundic mucosal cells. PGE2 production, stimulated by bradykinin, epidermal growth factor, zymosan, and calcium ionophore, was greater in the small-cell elutriator fraction (SCEF) than in the medium and large cell fractions, which contained mucous, chief, and parietal cells. Linear density gradients of SCEF cells revealed maximal PGE2 production in cells of light density. Mast, endocrine, and endothelial cells did not account for this PGE2 production. Macrophages, identified by uptake of acetylated-LDL, immunoreactivity with antibodies to the human Ia antigen, and phagocytosis of fluorescent latex particles, were enriched in the SCEF and correlated with PGE2 production in the density gradient. Magnetic separation of cells in the SCEF-ingesting iron particles enriched PGE2 production. Fractions enriched in endothelial cells present in intact capillary fragments, but depleted of macrophages, also produced PGE2. Regulation of PGE2 production differed among cell types. Fibroblasts were easily cultured from submucosa, but were not detected in the SCEF. We conclude that macrophages and capillary endothelial cells are major producers of PGE2 in the canine fundic mucosa.