Ultrastructure of ECL cells in Mastomys after long-term treatment with H2 receptor antagonist loxtidine.

Gastric ECL-cell hyperplasia and carcinoids (ECLoma) develop after 1 year in rats treated with omeprazole or 2 months in Mastomys treated with loxtidine. The aim of this study was to examine the ultrastructure of ECL cells in Mastomys after loxtidine treatment with an attempt to evaluate whether an impairment of autophagy was involved in the tumorigenesis. Mastomys were given loxtidine for 8 or 27 weeks. Morphological analysis of ECL cells showed that (1) cell size was not increased after 8 or 27 weeks; (2) secretory vesicles, a hallmark feature of welldifferentiated ECL cells, were unchanged after 8 weeks but reduced after 27 weeks; (3) granules were reduced after 8 or 27 weeks; (4) microvesicles were unchanged after the treatment; and (5) vacuoles and lipofuscin bodies were found occasionally after 8 weeks but not at 27 weeks. In addition, the appearance of ECL-cell ultrastructure differed between loxtidine-treated Mastomys and rats treated with omeprazole or subjected to antrectomy, but was similar between Mastomys treated with loxtidine for 27 weeks and mice deficient in CCK(2) receptor. We suggest that the ultrastructure of ECL cells in Mastomys after long-term treatment with loxtidine displayed an impaired formation of vacuoles and lipofuscin bodies, markers of the autophagic pathway.

Dedifferentiation of enterochromaffin-like cells in gastric cancer of hypergastrinemic cotton rats.

The role of enterochromaffin-like (ECL) cells in gastric carcinogenesis is not fully understood. Spontaneous tumours developing in hypergastrinemic female cotton rats have an adenocarcinoma phenotype, but numerous cells in the dysplastic mucosa as well as in the carcinomas are positive for neuroendocrine markers. In the present study of female cotton rats with 2 and 8 months' hypergastrinemia, the oxyntic mucosa of the stomach was examined histologically and immunolabelled for histidine decarboxylase (HDC) and pancreastatin, and hyperplastic and neoplastic ECL cells were evaluated by electron microscopy. These animals developed hyperplasia of the oxyntic mucosa in general and of the ECL cells in particular after 2 months and dysplasia and carcinomas after 8 months. The immunoreactivity of the ECL cells in the oxyntic mucosa was increased at 2 months and declined at 8 months. These histological changes were associated with progressive loss of secretory vesicles and granules in ECL cells. We suggest that ECL cells in hypergastrinemic cotton rats dedifferentiate with time and that the gastric carcinomas may develop from ECL cells.

Ultrastructure and chromogranin A immunogold labelling of ECL cell carcinoids.

Poorly differentiated neuroendocrine cells can be difficult to recognise. Sensitive methods are needed to label cells that have lost their ultrastructural features and have reduced concentrations of neuroendocrine markers. In gastric neoplasms, enterochromaffin-like cells might dedifferentiate and lose their characteristic granules and secretory vesicles, making detection of such cells increasingly difficult. However, chromogranin A (CgA) immunogold labelling could provide sensitive and specific detection of gastric neuroendocrine cells. We present ultrastructural findings, CgA immunogold labelling as well as conventional immunohistochemical findings of two human enterochromaffin-like cell carcinoids. Electron-dense granules of poorly differentiated cells were less intensely labelled than granules in well-differentiated cells. Granules with atypical shape as well as punctuate granules previously found in neuroendocrine neoplasms were also CgA labelled. The CgA labelling efficacy after antigen retrieval in an alkaline solution was higher after heating in an autoclave at 135 degrees C compared to a microwave at 100 degrees C for both granules and secretory vesicles without significant deterioration of the ultrastructure. In conclusion, the use of CgA immunogold labelling could ensure a specific classification of cells with neuroendocrine granules and be a supplement to immunohistochemical examination of poorly differentiated tumours.

Multiple gastric carcinoids and endocrine cell micronests in type A gastritis: Nuclear morphometric and immunohistochemical analysis.

While the hyperplasia-neoplasia sequence of enterochromaffin-like (ECL) cells has been proposed in the pathogenesis of type I gastric carcinoids, the criteria for distinction between hyperplastic endocrine cell micronest (ECM) and neoplastic ECM have not been established. The aims of this study were to clarify differences between the hyperplasia and neoplasia of ECL cells and determine the optimal classification system for gastric ECL cell proliferations in type A gastritis. Endocrine cell lesions (n=531) from 8 surgically-resected stomachs with type A gastritis were reclassified as either atrophic ECM (n=333), hyperplastic ECM (n=168), neoplastic ECM (all ECM > or =0.1 mm in size, n=15), or typical carcinoid (n=15). Hematoxylin and eosin-stained sections were semiautomatically analyzed by nuclear morphometry. Immunohistochemical expression of bcl-2, p53 and Ki-67 was also investigated. As the histologic grade of histology advanced, the morphometric values of area, circumference and largest diameter of the nuclei significantly increased (p<0.0005), while the frequency of diffuse expression of bcl-2 significantly decreased (p<0.0001). Significant differences were also observed in all morphometric parameters and in bcl-2 positivity between the hyperplastic ECM and neoplastic ECM group. There was no expression of p53 in any of the lesions. The Ki-67 index did not differ between the neoplastic ECM and typical carcinoid groups. These results suggest that our system of classification for gastric endocrine cell proliferations in type A gastritis is appropriate. Nuclear morphometry and bcl-2 immunoexpression are useful parameters for the distinction of neoplastic ECMs from hyperplastic ECMs.

Submucosal microinfusion of endothelin and adrenaline mobilizes ECL-cell histamine in rat stomach, and causes mucosal damage: a microdialysis study.

Rat stomach ECL cells release histamine in response to gastrin. Submucosal microinfusion of endothelin or adrenaline, known to cause vasoconstriction and gastric lesions, mobilized striking amounts of histamine. While the histamine response to gastrin is sustainable for hours, that to endothelin and adrenaline was characteristically short-lasting (1-2 h). The aims of this study were to identify the cellular source of histamine mobilized by endothelin and adrenaline, and examine the differences between the histamine-mobilizing effects of gastrin, and of endothelin and adrenaline. Endothelin, adrenaline or gastrin were administered by submucosal microinfusion. Gastric histamine mobilization was monitored by microdialysis. Local pretreatment with the H1-receptor antagonist mepyramine and the H2-receptor antagonist ranitidine did not prevent endothelin- or adrenaline-induced mucosal damage. Submucosal microinfusion of histamine did not cause damage. Acid blockade by ranitidine or omeprazole prevented the damage, suggesting that acid back diffusion contributes. Gastrin raised histidine decarboxylase (HDC) activity close to the probe, without affecting the histamine concentration. Endothelin and adrenaline lowered histamine by 50-70%, without activating HDC. Histamine mobilization declined upon repeated administration. Endothelin reduced the number of histamine-immunoreactive ECL cells locally, and reduced the number of secretory vesicles. Thus, unlike gastrin, endothelin (and adrenaline) is capable of exhausting ECL-cell histamine. Microinfusion of alpha-fluoromethylhistidine (known to deplete ECL cells but not mast cells of histamine) reduced the histamine-mobilizing effect of endothelin by 80%, while 1-week pretreatment with omeprazole enhanced it, supporting the involvement of ECL cells. Somatostatin or the prostanoid misoprostol inhibited gastrin-, but not endothelin-stimulated histamine release, suggesting that endothelin and gastrin mobilize histamine via different mechanisms. While gastrin effectively mobilized histamine from ECL cells in primary culture, endothelin had no effect, and adrenaline, a modest effect. Hence, the striking effects of endothelin and adrenaline on ECL cells in situ are probably indirect, possibly a consequence of ischemia.

Functional impairment of the individual rat stomach ECL cell in response to sustained hypergastrinemia.

ECL cells in the oxyntic mucosa secrete histamine and pancreastatin in response to gastrin. The present study examined gastrin-evoked ECL-cell responses over a 10-week time span in terms of individual ECL cells and unit ECL cell volume. Rats were treated with omeprazole (400 micromol/kg per day orally). The concentrations of gastrin and pancreastatin in serum and of histamine and pancreastatin in the oxyntic mucosa were measured as was the activity of the oxyntic mucosal histidine decarboxylase (HDC). The ECL cells were visualized by immunostaining of histamine and examined by electron microscopy. The total ECL cell number and volume, and the mean ECL cell diameter and volume were determined. The HDC, chromogranin A (CGA) and cholecystokinin-B (CCK-B) receptor mRNA concentrations were determined. In terms of individual ECL cells and unit ECL cell volume, the serum pancreastatin concentration, the oxyntic mucosal histamine content, HDC activity, and HDC, CGA and CCK-B receptor mRNA contents increased slowly at first and then leveled off or started to decline after 2 weeks. After 10 weeks all ECL-cell parameters (expressed per unit ECL cell volume) were back to or approaching the starting value. In conclusion, sustained hypergastrinemia first activates each individual ECL cell (with a peak after 1-2 weeks) and then causes gradual functional impairment, the activity returning towards the pre-stimulation level.

Neurohormonal regulation of histamine and pancreastatin secretion from isolated rat stomach ECL cells.

ECL cells are numerous in the acid-producing part of the rat stomach. They are rich in histamine and pancreastatin, a chromogranin A-derived peptide, and they secrete these products in response to gastrin. We have examined how isolated ECL cells respond to a variety of neuromessengers and peptide hormones. Highly purified (85%) ECL cells were collected from rat stomach using repeated counter-flow elutriation and cultured for 48 h before experiments were conducted. The ECL cells responded to gastrin, sulphated cholecystokinin-8 and to high K+ and Ca2+ with the parallel secretion of histamine and pancreastatin. Glycine-extended gastrin was without effect. Forskolin, an activator of adenylate cyclase, induced secretion, whereas isobutylmethylxanthine, a phosphodiesterase inhibitor, raised the basal release without enhancing the gastrin-evoked stimulation. Maximum stimulation with gastrin resulted in the release of 30% of the secretory products. Numerous neuromessengers and peptide hormones were screened for their ability to stimulate secretion and to inhibit gastrin-stimulated secretion. Pituitary adenylate cyclase activating peptide (PACAP)-27 and -38 stimulated secretion of both histamine and pancreastatin with a potency greater than that of gastrin and with the same efficacy. Related peptides, such as vasoactive intestinal peptide, helodermin and helospectin, stimulated secretion with lower potency. The combination of EC100 gastrin and EC50 PACAP produced a greater response than gastrin alone. None of the other neuropeptides or peptide hormones tested stimulated secretion. Serotonin, adrenaline, noradrenaline and isoprenaline induced moderate secretion at high concentrations. Muscarinic receptor agonists did not stimulate secretion, and histamine and selective histamine receptor agonists and antagonists were without effect. This was the case also with GABA, aspartate and glutamate. Somatostatin and galanin, but none of the other agents tested, inhibited gastrin-stimulated secretion. Our results reveal that not only gastrin but also PACAP is a powerful excitant of the ECL cells, that not only somatostatin, but also galanin can suppress secretion, that muscarinic receptor agonists fail to evoke secretion, and that histamine (and pancreastatin) does not evoke autofeedback inhibition.

Anatomical location of enterochromaffin-like (ECL) cells, parietal cells, and chief cells in the stomach demonstrated by immunocytochemistry and electron microscopy.

Enterochromaffin-like (ECL) cells are included in the endocrine cells present in the gastric oxyntic mucosa, and have been attracting attention as histamine-secreting cells contributing to gastric secretion. However, the anatomical location of ECL cells in relation to parietal cells and chief cells has not yet been sufficiently investigated. To elucidate this location of ECL cells, we performed an immunocytochemical study using anti-histamine antibody and electron microscopic examination of guinea pig gastric mucosa. ECL cells were located near the basement membranes in the gastric oxyntic region, and were in contact with both chief cells and parietal cells in the same glandular epithelium. The ratio of ECL cells in contact with chief cells was clearly greater than that in contact with parietal cells. An omega-shaped morphology, indicating emiocytosis, was found in ECL cells by electron microscopy. These findings suggest that ECL cells have a paracrine effect on chief cells and parietal cells, and may have an important physiological role in pepsinogen secretion.

Electron microscopic immunohistochemical investigation of chromogranin A in endocrine cells in human oxyntic gastric mucosa.

Human oxyntic gastric mucosa harbours 6 types of endocrine cells: enterochromaffin-like (ECL) cells, enterochromaffin (EC) cells, somatostatin (D) cells, and cells with an unknown secretory product (P cells, D1 cells and X (A-like) cells). In the present study, intracellular localization and granular content of chromogranin A (CGA) in these cells have been investigated by electron microscopic immunohistochemistry. The content of CGA in granules of the various types of endocrine cells was evaluated and compared with the content of serotonin and somatostatin in EC cells and D cells, respectively. ECL cells, EC cells, P cells, D1 cells and X cells contained CGA in their granules, whereas D cells did not. CGA granular content in ECL cells, P cells, D1 cells and X cells was 3.39 +/- 0.17, 3.41 +/- 0.21, 3.58 +/- 0.18, and 3.55 +/- 0.09, respectively. In ECL cells, CGA was also found in a nongranular form. The CGA content in EC cells (2.95 +/- 0.21) was not significantly different from the serotonin content (2.82 +/- 0.11; p > 0.05) which is in line with the basic significance of CGA as potential amine storage and release protein. The somatostatin content in D cells was 3.30 +/- 0.15. Our study has established high content of CGA in granules of all types of endocrine cells in human oxyntic gastric mucosa except in D cells.

ECL cells involvement in the isoproterenol-induced gastroprotection. An ultrastructural study.

The central and peripheral adrenergic systems are involved in the regulation of several functions in the gut including the maintenance of gastric microcirculation and gastric secretion but little is known about the role of the adrenergic system, in particular, beta-adrenoceptors in the phenomenon of gastroprotection. In this study acute gastric lesions were provoked by an intragastric (i.g.) application of 100% ethanol in rats with topical application of isoproterenol (ISO) (1 mg/kg) or subcutaneous (s.c.) administration of ranitidine (RAN) (40 mg/kg) or both. An area of gastric lesions was determined by planimetry, gastric blood flow (GBF) was determined by H2-gas clearance technique and gastric specimens were taken for histology and electron microscopy. It was found that ISO reduced ethanol-induced gastric mucosal lesions and this effect was accompanied by a rise in GBF. In contrast, RAN applied s.c. in a dose that produced almost complete achlorhydria, failed to affect ethanol-lesions but attenuated significantly ISO induced gastroprotection and abolished the increase in the GBF induced by this beta-adrenoceptor agonist. Histology and ultrastructural study revealed that pretreatment with ISO influenced HCl production reflected by the elaborated secretory surface of parietal cell intracellular canaliculi. All these changes were accompanied by the ultrastructural changes in Golgi apparatus in ECL-like cells (histamine storing cells). Pretreatment with ISO caused the collapse of Golgi profiles and only peripheral sacs were not compressed but such a change was not observed after RAN treatment. The best developed Golgi was, however, seen in the control rats without any treatment. Secretory granules in ECL cells were significantly expanded after pretreatment with ISO but did not show significant morphological changes in rats pretreated with RAN. We conclude that 1. ISO protects the gastric mucosa injured by ethanol presumably due to increased gastric microcirculation, and 2. ECL-like cells are actively involved in ISO-induced gastroprotection possibly by the increased histamine release which is reflected by ECL-cell and Golgi apparatus morphology.

Serum gastrin and gastric enterochromaffin-like cells during estrous cycle, pregnancy and lactation, and in response to estrogen-like agents in rats.

Histamine-containing enterochromaffin-like (ECL) cells are numerous in the gastric mucosa. They operate under the control of gastrin. ECL-cell tumors (gastric carcinoids) may arise as a consequence of sustained hypergastrinemia. For reasons unknown, such tumors have a female preponderance both in laboratory animals and humans. The present study consisted of four experiments exploring the possibility that gender-related factors might affect rat ECL cells. 1) A gender difference in terms of serum gastrin concentration and oxyntic mucosal histidine decarboxylase (HDC) activity appeared in Sprague-Dawley but not Wistar rats. Ultrastructural appearance of the ECL cells did not differ between genders. 2) During the different phases of the estrous cycle, the serum gastrin concentration, HDC activity and histamine concentration did not change. 3) During pregnancy, the serum gastrin concentration was suppressed, while it was increased during lactation. The HDC activity and the histamine concentration of the oxyntic mucosa were correlated with the levels of circulating gastrin. 4) Twelve-month treatment with estrogen-like agents, dieldrin and/or toxaphene (alone or in combination) was without any effect on the ECL cells neither in male nor in female rats. In conclusion, the ECL cells are under the control of gastrin, but probably not hormones that involve in the estrous cycle and pregnancy and lactation in rats. Possible gender-related factors behind the female preponderance of ECL-cell tumors remain unknown.

Neuroendocrine cells in diffuse gastric carcinomas: an ultrastructural study with immunogold labeling of chromogranin A.

Neuroendocrine differentiation is often found in gastric carcinomas, but the relevance of these cells in gastric carcinogenesis is debated. We applied immunolabeling at the electron microscopic level to study the ultrastructure of neuroendocrine cells in gastric carcinomas to ensure correct cellular classification of dedifferentiated cells. The immunogold labeling at electron microscopic level was compared with an established sensitive immunohistochemical method using light microscopy. Thirteen human gastric adenocarcinomas of the diffuse type were examined for neuroendocrine differentiation by chromogranin A (CgA) labeling at both the light and electron microscopic level. The ultrastructure of CgA-positive cells was compared with CgA-positive cells from controls. Nine of 13 tumors showed CgA-positive cells both at the light and electron microscopic level. The CgA-positive cells displayed altered ultrastructural features compared with controls. Some of the CgA-positive tumor cells had granules typical for enterochromaffin-like cells. Immunoelectron microscopy seems to provide both significant immunolabeling and sufficient ultrastructure to enhance classification of cells in neoplastic tissue.

ECL cell histamine mobilization and parietal cell stimulation in the rat stomach studied by microdialysis and electron microscopy.

AIM: Gastrin stimulates acid secretion by mobilizing histamine from enterochromaffin-like (ECL) cells that occur predominantly at the base of the gastric glands. The parietal cells occur higher up in the glands nearer to the gastric lumen. The present study was performed to assess whether histamine is transported from the ECL cell via the microcirculation (endocrine route) or local diffusion (paracrine route). METHODS: Totally isolated, vascularly perfused, rat stomachs were examined both in basal and gastrin-stimulated state. Histamine concentrations, determined by radioimmunoassay in venous effluent and microdialysate from an indwelling probe in the submucosa, were monitored over a period of 240 min. Gastrin-17 was infused through an arterial catheter for 120 min. The parietal cells were examined by electron microscopy, and the percentage of actively secreting parietal cells (displaying secretory canaliculi) in four regions along the glands (basal to surface, zones I-IV) was determined. RESULTS: Gastrin stimulated acid secretion and histamine release as well as parietal cell activation. Upon gastrin stimulation, histamine concentration in the microdialysate was 2.5-fold higher than in the venous effluent (P = 0.008). The parietal cells in the upper part of the gland (zone III) were found to be activated the most. CONCLUSION: As the histamine concentrations were higher in the tissue (microdialysate) than in blood, histamine seems to reach the parietal cells via the paracrine route. The fraction of active parietal cells seems to depend more on the age of the parietal cells than on the distance from the ECL cell.

Secretory organelles in ECL cells: effects of pharmacological blockade of the gastrin/CCK2 receptor versus its elimination by gene targeting.

Histamine-producing ECL cells are numerous in the stomach. They express gastrin/CCK2 receptors and respond to gastrin by releasing histamine. Ultrastructurally, they display numerous and very characteristic secretory organelles: granules, secretory vesicles and microvesicles. This paper focuses on the impact of the gastrin/CCK2 receptor on the ultrastructure of the ECL cells. The effects of pharmacological blockade of the receptor are compared with the effects of receptor elimination following selective gene targeting. Long-term administration of powerful gastrin/CCK2 receptor antagonists was found to induce hypotrophy of rat stomach ECL cells with reduced number of granules, secretory vesicles and microvesicles. In gastrin/CCK2 receptor knockout mice ECL cells, i.e., histamine-storing cells with the characteristic ultrastructure of ECL cells, had disappeared from the oxyntic mucosa and been replaced by a novel population of endocrine-like cells. These cells harbored granules and microvesicles, but were devoid of histamine and secretory vesicles. We suggest that the gastrin/CCK2 receptor is important for the proper differentiation of the ECL cells and for maintaining their characteristic ultrastructure.

Rat stomach ECL cells up-date of biology and physiology.

The ECL cell is the predominant endocrine cell type in the oxyntic mucosa, displaying typical ultrastructure with numerous cytoplasmic vesicles and electron-dense granules. ECL cells have many features in common with neurons and other peptide hormone-producing endocrine cells, including the ability to produce, store, and secrete chromogranin-A and chromogranin A-derived peptides. In addition, they produce and store histamine and respond with activation and growth to a gastrin challenge. ECL cells are stimulated to secrete histamine as well as other products by gastrin and PACAP and are inhibited by somatostatin, galanin, and prostaglandins. The cytoplasmic vesicles are thought to contain histamine and other secretory products. Mature secretory vesicles occur in the docking zone of the ECL cells, where they constitute the releasable pool of secretory products. Gastrin stimulation will induce exocytosis and degranulation. Histamine released from ECL cells plays a key role in the regulation of parietal cell activity (the gastrin-ECL cell-parietal cell axis). In response to long-term gastrin stimulation, vacuoles and lipofuscin bodies develop in the ECL cells, forming part of a crinophagic pathway by which the ECL cell strives to eliminate superfluous secretory products.

Differentiation of gastric ECL cells is altered in CCK(2) receptor-deficient mice.

BACKGROUND & AIMS: Gastrin stimulation of the type 2 cholecystokinin (CCK(2)) receptor results in ECL cell proliferation and histamine secretion. This report describes the effects of targeted disruption of the CCK(2) receptor gene on ECL cell morphology and function. METHODS: The ECL cells in the oxyntic mucosa of CCK(2) receptor-deficient (knockout [KO]) vs. wild-type (WT) mice were investigated by immunocytochemical and biochemical approaches, as well as by electron microscopy. RESULTS: Immunocytochemistry demonstrates similar numbers (cells per millimeter of horizontal length of mucosa) of pancreastatin- or vesicle monoamine transporter-2 (VMAT-2)-immunoreactive cells in WT mice and KO mice. However, only WT mice harbor histamine-immunoreactive ECL cells. The mucosal histamine content in KO mice (likely originating from mast cells) is only a minute fraction of that present in WT animals. The activity of the histamine forming enzyme, histidine decarboxylase (a marker of ECL cells), was undetectable in the oxyntic mucosa of KO mice yet was readily apparent in the mucosa from WT animals. Electron microscopy revealed numerous ECL cells in WT mice. In KO animals, these cells were replaced by an "ECL-like" cell type, characterized by a lack of secretory vesicles (a hallmark feature of normal ECL cells) and the presence of dense-core granules and microvesicles in numbers comparable to those found in WT ECL cells. Based on ultrastructural features, the ECL-like cells in KO mice can be readily distinguished from other gastric endocrine cells, including A-like cells and D cells. CONCLUSIONS: Absence of a single gene product, the CCK(2) receptor, alters the differentiation and function of gastric ECL cells.

Effects of reserpine on ECL-cell ultrastructure and histamine compartmentalization in the rat stomach.

The histamine-storing ECL cells in the stomach play a key role in the control of acid secretion. They contain granules, secretory vesicles and microvesicles, and sustained gastrin stimulation results in the additional formation of vacuoles and lipofuscin bodies. The cells are rich in the vesicle monoamine transporter type-2 (VMAT-2), which can be inhibited by reserpine. The present study examines the effect of reserpine on ECL-cell ultrastructure and histamine compartmentalization. Rats received reserpine and/or gastrin. Reserpine was given twice by the intraperitoneal route (25 mg/kg once daily). Gastrin-17 was given by subcutaneous infusion (5 nmol/kg/h), starting at the time of the first reserpine injection and continuing for 4 days when the rats were killed. At this stage, histamine in the oxyntic mucosa was unaffected by reserpine but elevated by gastrin. Immunocytochemical analysis (confocal microscopy) showed ECL-cell histamine in control and gastrin-treated rats to be localized in cytoplasmic organelles (e.g., secretory vesicles). After treatment with reserpine alone or reserpine+gastrin, ECL-cell histamine occurred mainly in the cytosol. Planimetric analysis (electron microscopy) of ECL cells showed reserpine to increase the number, size and volume density of the granules and to reduce the size and volume density of the secretory vesicles. Gastrin reduced the number and volume density of granules and secretory vesicles, increased the number and volume density of microvesicles and caused vacuoles and lipofuscin bodies to appear. Reserpine+gastrin increased the number, volume density and size of the granules. Reserpine prevented the effects of gastrin on secretory vesicles, vacuoles and microvesicles, but did not prevent the development of lipofuscin. Our findings are in line with the views: (1) that preformed cytosolic histamine is taken up by granules/secretory vesicles via VMAT-2, that histamine is instrumental in the transformation of granules into secretory vesicles and in their consequent enlargement and (2) that vacuoles are formed by the fusion of large secretory vesicles.

Gastric phenotypic abnormality in cholecystokinin 2 receptor null mice.

Gastrin, released from antral G-cells, plays an important role in the regulation of gastric acid secretion and is trophic for the stomach. The cholecystokinin type 2 (CCK)2 receptor (previously referred to as CCK-B/gastrin receptors) is expressed in both parietal cells and ECL cells in the oxyntic mucosa of stomach. Gastric phenotypic abnormality has been observed in CCK2 receptor null (gene knock-out) mice. Such mice displayed markedly impaired gastric acid secretion, atrophy of the oxyntic mucosa and hypergastrinaemia. The impaired acid secretion may be the result of a reduced parietal cell mass, a reduced proportion of actively secreting parietal cells (with secretory canaliculi), and a replacement of ECL cells by histamine-free ECL-like cells. The ECL-like cells, observed in the CCK2 receptor null mice, lacked the hallmark features of wild-type ECL cells, i.e. histamine and cytoplasmic secretory vesicles. However, they had the features of endocrine cells, such as the content of pancreastatin (a fragment of chromogranin A), with cytoplasmic small dense-core granules and microvesicles. We propose that the replacement of ECL cells by ECL-like cells in the mutant mice reflects an altered differentiation of the same precursors that develop into ECL cells in wild-type mice. Thus, studies of CCK2 receptor null mice demonstrate the importance of the receptor in the regulation of gastric acid secretion and in the differentiation of ECL cells in the oxyntic mucosa of stomach.

Immunoelectron microscopic study for histamine in the gastric enterochromaffin-like cells of rats treated with the proton pump inhibitor lansoprazole.

The enterochromaffin-like (ECL) cells of the gastric mucosa in animals play an important role in gastric acid secretion. They contain few granules and numerous secretory vesicles and microvesicles. They operate under the control of circulating gastrin. In the present study, we conducted an immunoelectron microscopic study for histamine (HA) in the ECL cells of rats given the proton pump inhibitor lansoprazole (LP), which is known to induce hypergastrinemia. The pre-embedding indirect immunoperoxidase procedure utilized a mouse monoclonal antibody AHA-2 against glutaraldehyde-conjugated HA. Rats received LP (50 microg/kg per day, subcutaneously) over a period of a month, and developed hypertrophy of the ECL cells in the stomach. It was clearly demonstrated that HA was located to a much higher degree in the cytoplasm of ECL cells of LP-treated rats than in normal rats. HA immunoreactivity was observed in the cores of the granules and secretory vesicles of the ECL cells in all the rats, but in the LP-treated rats it was observed in the cores of the newly developed vacuoles as well. These results may suggest that HA may be actively generated in the cytoplasm of the hypertrophic ECL cells of LP-treated rats. Also suggested in the present study is that HA is instrumental in the transformation of granules into secretory vesicles and in their consequent enlargement, and that vacuoles are formed by the fusion of large secretory vesicles. Furthermore, the finding that relatively little HA immunoreactivity existed in the vacuoles may suggest that the vacuoles actively degrade superfluous secretory products (for example, HA) through enhanced autophagocytosis and/or oxidative stress. Another possibility may be that the membrane-bounded structure regarded as the vacuoles in this study might actually be an invagination structure produced as a result of successive series of exocytosis through which the secretory vesicles actively and rapidly release HA.