Gastric Enterochromaffin-like Cells Research Articles

Serum gastrin and chromogranin A during medium- and long-term acid suppressive therapy: a case-control study.

Serum chromogranin A (CgA) is regarded as a reliable marker of neuroendocrine proliferation. We previously described increased serum CgA levels during short-term profound gastric acid inhibition. To investigate serum gastrin and CgA levels in dyspeptic patients during continuous medium- (6 weeks to 1 year), or long-term (1-8 years) gastric acid suppressive therapy. 114 consecutive dyspeptic patients referred for upper gastrointestinal endoscopy were enrolled in a cross-sectional, case-control study [62 patients on continuous antisecretory therapy, either with proton pump inhibitors (n = 47) or H2-receptor antagonists (H2RA) (n = 15) for gastro-oesophageal reflux disease with or without Barrett's oesophagus or functional dyspepsia, and 52 age- and sex-matched patients without medical acid inhibition and with normal endoscopic findings (control group)]. Omeprazole doses ranged from 20 mg to 80 mg daily and ranitidine from 150 mg to 450 mg daily. Fasting serum CgA and serum gastrin levels were measured by radioimmunoassay (reference values: serum CgA < 4.0 nmol/L; serum gastrin < 85 ng/L). Fasting serum CgA levels positively correlated with serum gastrin in the entire study population (r = 0. 55, P = 0.0001). Median serum CgA values were higher in patients treated with a proton pump inhibitor than H2RA [2.8 (2.0-5.9) nmol/L vs. 2 (1.9-2.3) nmol/L, P < 0.002] and controls [2.8 (2.0-5.9) nmol/L vs. 1.8 (1.5-2.2) nmol/L, P < 0.0001) and did not differ between patients treated with H2RA or controls. Serum gastrin and CgA levels in patients on proton pump inhibitor therapy positively correlated with the degree and duration of acid inhibition. Patients on long-term proton pump inhibitor therapy had significantly higher fasting serum gastrin and CgA than those on medium-term proton pump inhibitor therapy [127 (73-217) ng/L vs. 49 (29-78) ng/L, P < 0.0001 and 4.8 (2.8-8) ng/L vs. 2.1 (1.9-2.6) ng/L, P < 0.001]. No such relation was found in patients on medium- vs. long-term H2RA. Overall, patients with positive Helicobacter pylori serology had higher serum gastrin and CgA levels than those with negative H. pylori serology [51 (27-119) ng/L vs. 27 (14-79) ng/L, P = 0.01, 2.4 (1.9-3.4) nmol/L vs. 2.0 (1.7-2.5) nmol/L, P = 0.05]. During long-term continuous proton pump inhibitor treatment, serum gastrin and CgA levels are significantly elevated compared to H2RA treatment and nontreated dyspeptic controls. H. pylori infection seems to affect gastric ECL cell secretory function. Increased serum CgA values during long-term profound gastric acid inhibition could reflect either gastric enterochromaffin-like cell hyperfunction or proliferative changes.

Regenerating gene protein may mediate gastric mucosal proliferation induced by hypergastrinemia in rats

Background & Aims: Regenerating gene ( Reg) has been isolated from rat regenerating pancreatic islets, and Reg protein is mitogenic to islet cells. We have recently shown that Reg gene and Reg protein are expressed in gastric enterochromaffin-like (ECL) cells. This study aimed to clarify whether gastrin enhances Reg protein production in ECL cells and whether Reg protein is mitogenic to gastric mucosal cells. Methods: Reg gene expression in response to acute and chronic hypergastrinemia was investigated in rats. Immunohistochemical studies, Northern blotting, and in situ hybridization were performed to investigate the expression of Reg protein and Reg gene. The direct effect of gastrin on Reg gene expression was investigated using isolated ECL cells, and the trophic effect of Reg protein on cultured gastric epithelial cells was assessed by [ 3H]thymidine uptake. Results: Both chronic hypergastrinemia and short-term gastrin administration stimulated Reg gene expression and Reg protein production in fundic mucosa. Reg gene expression was also augmented in isolated ECL cells after incubation with rat gastrin. Reg protein was mitogenic to cultured rat gastric epithelial cells. Conclusions: Gastrin stimulates the production of Reg protein in gastric ECL cells, which may be involved in the gastrin-induced gastric mucosal cell growth. GASTROENTEROLOGY 1998;115:1483-1493

Omerprazole and other proton pump inhibitors: pharmacology, efficacy, and safety, with special reference to use in children.

Omerprazole and other proton pump inhibitors: pharmacology, efficacy, and safety, with special reference to use in children.

A polyamine pathway-mediated mitogenic mechanism in enterochromaffin-like cells of Mastomys.

We have previously demonstrated that in Mastomys species proliferation of gastric enterochromaffin-like (ECL) cells is predominantly regulated by gastrin and by transforming growth factor-alpha (TGF-alpha) in the naive and neoplastic state, respectively. In this study we examined whether these intracellular mitogenic responses are mediated by polyamines and ornithine decarboxylase (ODC), the rate-limiting enzyme for polyamine biosynthesis. An ECL cell preparation of high purity was used to measure the effect of the polyamine derivatives putrescine, spermidine, and spermine on DNA synthesis by bromodeoxyuridine uptake. Both putrescine and spermidine augmented gastrin-stimulated, but not basal, DNA synthesis in naive cells. This proliferative response correlated with an increase in ODC activity that was partially inhibited (20%) by difluoromethylornithine (DFMO), an inhibitor of ODC (IC50, 30 pM). In contrast, all polyamines increased both basal and TGF-alpha-stimulated DNA synthesis as well as ODC activity in tumor ECL cells. DFMO completely inhibited the proliferative response of TGF-alpha (IC50, 3 pM). Thus polyamine biosynthesis is involved in proliferation of ECL cells and in particular the mitogenesis of tumor cells, suggesting a role for this pathway in the regulation of ECL cell transformation.

Growth factors control apoptosis of rat gastric enterochromaffin-like cells

Growth factors control apoptosis of rat gastric enterochromaffin-like cells

Voltage-gated Ca2+ currents in rat gastric enterochromaffin-like cells.

Enterochromaffin-like (ECL) cells are histamine-containing endocrine cells in the gastric mucosa that maintain a negative membrane potential of about -50 mV, largely due to voltage-gated K+ currents [D. F. Loo, G. Sachs, and C. Prinz. Am. J. Physiol. 270 (Gastrointest Liver Physiol. 33): G739-G745, 1996]. The current study investigated the presence of voltage-gated Ca2+ channels in single ECL cells. ECL cells were isolated from rat fundic mucosa by elutriation, density gradient centrifugation, and primary culture to a purity > 90%. Voltage-gated Ca2+ currents were measured in single ECL cells using the whole cell configuration of the patch-clamp technique. Depolarization-activated currents were recorded in the presence of Na+ or K+ blocking solutions and addition of 20 mM extracellular Ca2+. ECL cells showed inward currents in response to voltage steps that were activated at a test potential of around -20 mV with maximal inward currents observed at +20 mV and 20 mM extracellular Ca2+. The inactivation rate of the current decreased with increasingly negative holding potentials and was totally abolished at a holding potential of -30 mV. Addition of extracellular 20 mM Ba2+ instead of 20 mM Ca2+ increased the depolarization-induced current and decreased the inactivation rate. The inward current was fully inhibited by the specific L-type Ca2+ channel inhibitor verapamil (0.2 mM) and was augmented by the L-type Ca2+ channel activator BAY K 8644 (0.07 mM). We conclude that depolarization activates high-voltage-activated Ca2+ channels in ECL cells. Activation characteristics, Ba2+ effects, and pharmacological results imply the presence of L-type Ca2+ channels, whereas inactivation kinetics suggest the presence of additional N-type channels in rat gastric ECL cells.

Effect of Aging on Gastrin Receptor Gene Expression in Rat Stomach

Waki, S., Y. Kinoshita, H.-Y. Wang, M. Asahara, Y. Matsushima, M. S. Hassan, A. Okada, T. Maekawa, H. Fukui, C. Kawanami, K. Kishi and T. Chiba. Effect of aging on gastrin receptor gene expression in rat stomach. Peptides 19(2) 225–229, 1998.—Gastrin is a pivotal humoral factor which regulates gastric acid secretion through its receptors. There is no report, however, concerning the age-related changes of gastrin receptor gene expression in the stomach. Northern blot analysis and in situ hybridization were performed to clarify the changes of gastrin receptor expression during the aging. In situ hybridization clarified that gastrin receptor mRNA was expressed mainly in enterochromaffin-like (ECL) cells in adult rat gastric mucosa. With aging, gastrin receptor gene expression in the stomach increased with the concomitant increase in histidine decarboxylase mRNA. Since histidine decarboxylase is a marker of gastric ECL cells, the augmented gastrin receptor mRNA in aged rats may be caused by the increased ECL cells in gastric mucosa during the aging.

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.

Functional Importance of Synaptobrevin and SNAP-25 during Exocytosis of Histamine by Rat Gastric Enterochromaffin-Like Cells

Functional Importance of Synaptobrevin and SNAP-25 during Exocytosis of Histamine by Rat Gastric Enterochromaffin-Like Cells

The multiple endocrine neoplasia type I gene locus is involved in the pathogenesis of type II gastric carcinoids

BACKGROUND & AIMS: Both gastrin and genetic factors were suggested to underlie the pathogenesis of multiple gastric enterochromaffin-like (ECL) cell carcinoids. To assess the role of genetic alterations in carcinoid tumorigenesis, loss of heterozygosity (LOH) at the locus of the multiple endocrine neoplasia type 1 (MEN-1) gene was studied in gastric carcinoids of patients with MEN-1 and chronic atrophic type A gastritis (A-CAG), as well as in sporadically arising intestinal carcinoids. METHODS: DNA extracted from archival tissue sections of 35 carcinoid tumors was assessed for LOH with eight polymorphic markers on chromosome 11q13. A combined tumor and family study was performed in 1 patient with MEN-1-Zollinger-Ellison syndrome (ZES). RESULTS: LOH at 11q13 loci was detected in 15 of 20 (75%) MEN-1-ZES carcinoids, and each ECL-cell carcinoid with LOH showed deletion of the wild-type allele. Only 1 of 6 A-CAG carcinoids displayed LOH at the MEN-1 gene locus, and none of the 9 intestinal and rectal carcinoids showed 11q13 LOH. CONCLUSIONS: Gastric ECL-cell carcinoid is an independent tumor type of MEN-1 that shares a common developmental mechanism (via inactivation of the MEN-1 gene) with enteropancreatic and parathyroid MEN-1 tumors. Further analysis of sporadic and A-CAG carcinoids is needed to elucidate genetic factors involved in their tumorigenesis. (Gastroenterology 1997 Sep;113(3):773-81)

Gastric ECL-cell hyperplasia produces enhanced basal and stimulated gastric acid output but not gastric erosion formation in the rat

1. 1. The purpose of this study was to examine the change in gastric acid output and gastric erosion formation produced by inducing gastric enterochromaffinlike (ECL) cell hyperplasia in female rats. 2. 2. Rats were treated with vehicle or ranitidine (1,200 μmol/kg/day×4 wks) administered via SC Alzet minipumps. Experiments were performed 24 hours after removing the minipump, when the inhibitory effect of ranitidine on gastric acid secretion had been lost. 3. 3. Basal gastric acid secretion was 7-fold higher in chronic ranitidine animals than in sham control. 4. 4. Both total and net gastric acid secretions stimulated by carbachol/pentagastrin infusion or histamine injection were significantly higher in chronic ranitidine animals than in controls. 5. 5. By contrast, intracisternal injection of the chemical vagal stimulant RX77368 (100 ng) resulted in no net increase in acid output of the recovered ranitidine-pretreated group. 6. 6. No significant changes in gastric erosions produced experimentally by cold exposure plus restraint or indomethacin pretreatment were noted in recovered chronic ranitidine animals compared to sham controls. 7. 7. These findings suggest that achlorhydria-induced ECL cell hyperplasia augments both basal and stimulated gastric acid secretory function. The histamine results implicate an enhanced parietal cell mass, upregulation of H 2 receptors, and/or second-messenger events at the parietal cell as the mechanism for the enhanced gastric secretory response.

Functional impairment of rat enterochromaffin-like cells by interleukin 1 beta

BACKGROUND & AIMS: Histamine-producing enterochromaffin-like (ECL) cells play an integrative role in the regulation of acid secretion. Decreased mucosal histamine concentrations and increased levels of interleukin (IL) 1 beta, IL-6, and IL-8 have been detected in the gastric mucosa inflamed with Helicobacter pylori. The aim of this study was to investigate the response of isolated ECL cells to these cytokines.METHODS: Enriched rat gastric ECL cells (85%-95%) were cultured for 2-4 days.RESULTS: Polymerase chain reaction showed IL-1 and IL-6, but not IL-8 receptors, in ECL cell complementary DNA. Positive receptor staining with biotinylated IL-1 beta corresponded to ECL cell enrichment (92%). IL-6 and IL-8 had no effect on histamine secretion. IL-1 beta (2 U/mL) stimulated basal histamine secretion and nitric oxide production within 60 minutes and cyclic guanosine monophosphate production within 20 minutes. Pretreatment for 20 minutes with IL-1 beta (2 U/mL) attenuated gastrin-stimulated histamine secretion by 40%-50%, reversed by the IL-1 receptor antagonist (10 U/ mL). Pretreatment for 20 minutes with IL-1 beta (2 U/mL) completely inhibited gastrin-stimulated (1 nmol/L) histidine decarboxylase activity. IL-1 beta (2 U/mL, 60 minutes) increased lactate dehydrogenase release to 25% of cell content. Cells pretreated with IL- 1 beta did not respond to gastrin after a further 48-hour culture and showed decreased histamine content.CONCLUSIONS: ECL cells appear to express IL-1 receptors. IL-1 beta causes sustained functional impairment of ECL cells in vitro.(Gastroenterology 1997 Feb;112(2):364-75)

Monoclonal antibodies against glutaraldehyde-conjugated histamine: application to immunocytochemistry.

We have developed mouse monoclonal antibodies (AHA-1-5, all IgG1 sub-isotype mAbs) against histamine (HA) conjugated to bovine serum albumin using glutaraldehyde-NaBH4. Among these, AHA-1 mAb was found to be the most useful for HA immunocytochemistry (ICC) in terms of specificity and sensitivity without non-specific immunobinding. AHA-1 was demonstrated to be specific to HA with an enzyme-linked immunosorbent assay (ELISA) binding test, simulating the ICC of tissue sections, and not reactive to any of the other amino acids and peptides with N-terminal histidine tested. By use of this antibody, indirect immunoperoxidase staining was observed in rat stomach fixed with glutaraldehyde (GA) in combination with NaBH4 reduction. In contrast, no immunoreactivity was seen in tissue fixed only with GA. Absorption controls indicated that the immunostaining could be completely inhibited by GA-conjugated HA, which was consistent with the results of an ELISA inhibition test. No cross-reactivity occurred with other GA-conjugated amino acids. ICC staining was dense in the cytoplasm of gastric enterochromaffin-like cells and very weak in mast cells. A new finding was that staining was noticed in some cell bands of the intermediate layer between the stratum lucidum and the stratum corneum of the stratified squamous epithelium of the gastric cardia, esophagus, tongue, and skin in rats. The results strongly suggest that the monoclonal antibody allowed highly specific detection of HA in animal tissues.

Peptide YY inhibition of rat gastric enterochromaffin-like cell function

BACKGROUND & AIMS: The cellular target for peptide YY (PYY) inhibition of gastric acid secretion is unknown. The aim of this study was to determine whether PYY inhibits histamine release from isolated enterochromaffin-like (ECL) cells by stimulation of a selective Y receptor. METHODS: Isolated rat gastric ECL cells were analyzed in short-term culture for histamine release and for changes in intracellular calcium concentration using video imaging. RESULTS: Gastrin-stimulated histamine release was inhibited with a 50% inhibiting concentration of 2.10(-9) mol/L. Inhibition of histamine release and of calcium entry by PYY and [Pro34]PYY and no effect of PYY(3-36) characterizes an inhibitory Y1 receptor subtype. Reverse- transcription polymerase chain reaction of ECL cell RNA showed that the receptor was the nontruncated Y1 isoform. The inhibitory action of PYY and related peptides on gastrin-stimulated histamine release and calcium signaling was eliminated by pretreatment with 200 ng/mL pertussis toxin. Additive but not synergistic inhibitory effects of PYY and somatostatin on gastrin-stimulated histamine release were observed. CONCLUSIONS: Activation of a Y1 inhibitory receptor subtype present on the gastric ECL cell that inhibits gastrin-induced ECL cell histamine release and Ca2+ entry by activation of a Gi or G(o) class of protein may account for inhibition of gastric acid secretion by PYY released from the small intestine. (Gastroenterology 1997 Jan;112(1):127-35)

Somatostatin receptor regulation of gastric enterochromaffin-like cell transformation to gastric carcinoid

Although somatostatin is recognized as an inhibitor of neuroendocrine cell secretion, its effect on cell proliferation has not been well defined. Generation of low acid and hypergastrinemia through irreversible H2-receptor blockade (loxtidine) in the African rodent mastomys results in gastric carcinoids (ECLomas) within 4 months. This study was undertaken to evaluate and characterize the precise somatostatin receptor (SSTR) subtype on the mastomys enterochromaffin-like (ECL) cell and to define its role in the regulation of ECL cell secretion and proliferation. A pure preparation (approximately 90%) of ECL cells was derived by a combination of pronase digestion and density gradient separation. We assessed the effect of somatostatin (10(-15) to 10(-7) mol/L) on gastrin-stimulated ECL cell histamine secretion and DNA synthesis (bromodeoxyuridine uptake). SSTR2 subtype was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) using gene specific primers and mRNA isolated from normal and hypergastrinemia-induced ECLoma. The polymerase chain reaction product was confirmed by Southern analysis, subcloned, and sequenced. Somatostatin inhibited both gastrin-stimulated histamine secretion (IC50, 5 x 10(-13) mol/L) and DNA synthesis (IC50, 10(-10) mol/L). SSTR2 was identified in the mastomys' brain, and both normal and tumor ECL cells and comparison of the brain and ECL cell SSTR2 nucleotide sequences revealed homology of 99%. The SSTR2 is expressed by the mastomys' ECL cell and ECLoma. Receptor activation inhibits both ECL cell secretory and proliferative functions.

Reg gene expression is increased in rat gastric enterochromaffin-like cells following water immersion stress

BACKGROUND & AIMS: Reg gene has been isolated from regenerating rat pancreatic islets, and subsequent studies have shown a trophic effect of Reg protein on islet cells. However, little is known about the role of Reg protein in the stomach. The aim of this study was to clarify the localization of Reg messenger RNA (mRNA) and its product in the stomach and to examine changes in the level of their expression during regeneration of gastric mucosal cells. METHODS: Gastric lesions were experimentally induced in Sprague-Dawley rats by water immersion stress. Northern blot analysis and in situ hybridization studies were performed to examine changes in mRNA levels. Immunohistochemical studies were performed to identify the cellular localization and to investigate the change in Reg protein level. RESULTS: Reg mRNA and its product were distributed in the basal part of the oxyntic mucosa and were expressed mainly in enterochromaffin-like cells. Levels of both Reg mRNA and its product were markedly increased in the water immersion- induced gastric lesions. CONCLUSIONS: Reg mRNA and its product are expressed in gastric enterochromaffin-like cells, and their levels are increased during the healing process of water immersion-induced gastric lesions. (Gastroenterology 1996 Jul;111(1):45-55)

Importance of gastrin and other growth-factors in growth regulation of rat gastric enterochromaffinlike (ECL) cells in primary culture

Importance of gastrin and other growth-factors in growth regulation of rat gastric enterochromaffinlike (ECL) cells in primary culture

Potassium and chloride currents in rat gastric enterochromaffin-like cells.

The gastric enterochromaffin-like (ECL) cell secretes histamine in response to secretagogues (gastrin, acetylcholine) by calcium signaling-dependent exocytosis of intracellular vacuoles containing the hormone. ECL cells were isolated from rat fundic gastric mucosa by elutriation and density-gradient centrifugation. Currents across the plasma membrane were measured using whole cell patchclamp methods. These cells had a low conductance of 0.5 nS and resting potential of -50 mV. Depolarization activated a K+ current that was blocked by Ba2+. Steady-state current in absence of K+ was due to Cl- because of the magnitude of the reversal potential and the effects of Cl- removal. Stimulation of secretion by gastrin, cholecystokinin octapeptide (CCK-8), and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate activated the Cl- conductance with a time course similar to that of histamine release. Therefore the ECL cell maintains a high resting potential, largely due to K+ currents, and stimulation of secretion activates a Cl- current, perhaps deriving from the membrane of the secretory granule that fuses with the plasma membrane. The depolarization that ensues may activate the K+ current to maintain the membrane potential during exocytosis.

Involvement of BCL-2 Oncoprotein in the Development of Enterochromaffin-like Cell Gastric Carcinoids

To evaluate the involvement of the apoptosis-suppressing protein BCL-2 in the gastrin-dependent mechanism of induction of gastric enterochromaffin-like (ECL) cell carcinoids, the endocrine cell of the oxyntic mucosa were immunohistochemically investigated in (a) 10 normogastrinemic subjects with histologically normal gastric mucosa; (b) 22 patients with endocrine cell hyperplasia and affected by hypergastrinemic conditions with different risk of gastric carcinoid development, such as sporadic Zollinger-Ellison syndrome (sZES; n = 9), ZES associated with multiple endocrine neoplasia-1 (MEN-1; n = 4), and atrophic fundal gastritis (AFG; n = 9); (c) 14 patients with ECL gastric carcinoids accounting for a total of 31 tumors investigated. In the normal oxyntic mucosa, BCL-2 was consistently expressed by a subset of endocrine cells accounting for 50.0% (median; range, 24.6-74.0%) of the total number of endocrine cells immunostained for chromogranin A (CgA) in consecutive sections. BCL-2 immunoreactive cells were located mostly in the middle mucosal layer, suggesting a role for the protein during downward migration of maturing endocrine cells. No BCL-2 immunoreactivity was found in other specialized gastric epithelial cells. Expression of BCL-2 by hyperplastic oxyntic endocrine cells (mostly ECL cells) varied in parallel with the risk of carcinoid development. In fact, the ratio of BCL-2- to CgA-immunoreactive cells was reduced (median, 4.6%; p less than 0.0001; range, 0.9-42.0%) in sZES, a condition showing virtually no risk, unchanged (median, 55.6%; range 29.4-83.8 %) in cases of MEN-1/ZES with intermediate risk, and increased (median 87.6%; p less than 0.014; range, 48.8-199.4%) in cases of AFG, a condition at the highest risk of carcinoid. In ECL cell carcinoids, BCL-2 expression varied markedly from one tumor to another even in the same patient and was low or absent in most cases. In both hyperplastic and neoplastic ECL cells, an inverse relation between BCL-2 expression and CgA immunoreactivity, that is, the cell granule content, was found. These results suggest that BCL-2 expression by hyperplastic ECL cells is independent of the influence of serum gastrin and may contribute to the development of ECL cell carcinoid tumors by extending cell exposure to oncogenic factors. Once a carcinoid tumor is established, BCL-2 expression becomes inconsistent.

Gastrin stimulation of histamine synthesis in enterochromaffin-like cells from rabbit fundic mucosa

This work aimed to investigate the molecular role of gastrin in histamine synthesis in isolated rabbit fundic mucosal cells enriched in enterochromaffin-like (ECL) cells (37%). Gastrin stimulated histidine decarboxylase (HDC) activity by increasing the maximal velocity (Vmax) from 0.240 +/- 0.017 (basal value) to 0.332 +/- 0.012 pmol/mg protein/h and by decreasing the Michaelis-Menten constant value -Km; 73.90 +/- 2.2 vs. 93.42 +/- 4.32 microM (basal value)]. Pertussis toxin (PTX) (200 ng/ml) reduced the stimulation of HDC induced by 10 nM gastrin from 41.8 to 15.9%, whereas cholera toxin (CTX) (100 ng/ml) was without effect. Staurosporine and polymyxin B inhibited in a dose dependent manner the HDC activity stimulated by 10 nM gastrin. Phorbol 12-myristate 13-acetate (PMA; 100 nM) decreased Vmax (0.558 +/- 0.021 pmol/ mg protein/h) but did not change the Km. Furthermore, cycloheximide (0.1-10 microM) inhibited the gastrin-induced stimulation of HDC activity, whereas actinomycin D (up to 10 microM) was without effect. Finally, incubation of cells with gastrin (10 microM) left the expression of HDC mRNA unchanged. We concluded that gastrin, acting through "gastrin/CCK-B type" receptors coupled to PTX-sensitive G protein, exerts a short-term regulation of histamine synthesis in gastric ECL cells by increasing both the affinity of HDC for L-histidine and the number of active enzyme molecules. This last event, related to protein kinase C activation, could be due to a translational or posttranslational mechanism.