Parietal Cells Of Gastric Mucosa Research Articles

Basolateral expression of GRP94 in parietal cells of gastric mucosa

GRP94 is a member of the heat shock protein family normally confined to the endoplasmic reticulum that sometimes escapes the KDEL-mediated retention system. It is overexpressed in some gastric and other gastrointestinal carcinomas, but little is known about the physiological role of GRP94 in gastric mucosa. We investigated the membrane presence of GRP94 in parietal cells, which secrete acid into the gastric lumen, using subcellular fractionation, selective solubilization of membrane proteins, Western blotting, and radio-ligand binding and provided evidence of functional GRP94 expression at the surface of gastric mucosa parietal cells anchored to the basolateral domain. Our results show that GRP94 is not an integral membrane protein since 50 mM Na2CO3 treatment dissociates part of it from the membrane. However, 100 mM Na2CO3 treatment did not extract all GRP94 from the membrane, which indicates that it is strongly associated with it. The presence of GRP94 in isolated plasma membrane was demonstrated by Western blotting and its functionality by radio-ligand binding experiments. Both the K(D) value obtained in saturation experiments with N-ethylcarboxamido-[3H]adenosine at 4°C, at the nanomolar range, and the inhibition constant of its binding by radicicol, the most specific GRP94 inhibitor, indicate that active receptor regions are exposed at the membrane surface. Western blotting of plasma membrane subfractions showed that GRP94 is mainly expressed in the basolateral membrane of gastric parietal cells, while its presence in the apical domain is negligible, thereby inferring a role for GRP94 in processes operating in this membrane domain.

Immunocytochemical identification of low-affinity NTS2 neurotensin receptors in parietal cells of human gastric mucosa

The biological effects of neurotensin (NT) are mediated by two distinct G protein-coupled receptors, NTS(1) and NTS(2). Although it is well established that neurotensin inhibits gastric acid secretion in man, the plasma membrane receptor mediating these effects has not been visualized yet. We developed and characterized a novel antipeptide antibody to the carboxy-terminal region of the human NTS(2) receptor. The cellular and subcellular distribution of NTS(2) receptors was evaluated in various human gastrointestinal tissues. Specificity of the antiserum was demonstrated by (1) detection of a broadband migrating at M(r) 90 000-100 000 in Western blots of membranes from NTS(2)-expressing tissues; (2) cell-surface staining of NTS(2)-transfected cells; (3) translocation of NTS(2) receptor immunostaining after agonist exposure; and (4) abolition of tissue immunostaining by preadsorbtion of the antibody with its immunizing peptide. In the gastrointestinal tract, NTS(2) receptor immunoreactivity was highly abundant in parietal cells of the gastric mucosa, in neuroendocrine cells of the stomach small and large intestine, and in cells of the exocrine pancreas. NTS(2) receptors were clearly located in the plasma membrane and uniformly present on nearly all target cells. The presence of NTS(2) receptors was rarely detected in human tumors. This is the first localization of NTS(2) receptors in human formalin-fixed, paraffin-embedded tissues at the cellular level. The abundant expression of low-affinity NTS(2) receptors on the plasma membrane of human parietal cells provides a morphological substrate for the direct inhibition of gastric acid secretion observed after i.v. administration of neurotensin.

A Combined Experimental and Quantum Chemical Study on the Putative Protonophoric Activity of Thiocyanate

Inhibition of gastric acid secretion by thiocyanate is explained by a protonophoric mechanism assuming that thiocyanate induces a H + back flux from the acidic gastric lumen into the parietal cells of gastric mucosa. Protonophoric activity of thiocyanate was examined by swelling measurements using rat liver mitochondria and theoretically by quantum chemical methods. Mitochondria suspended in K-thiocyanate medium plus nigericin (an H/K-exchanger) swelled when the medium pH was acidic, indicating that SCN − initiates a transfer of H + across the inner membrane. To rationalize the protonophoric activity of thiocyanate, we considered the dehydration of SCN − to be critical for transmembranal H + transfer. For modeling this process, various hydrate clusters of SCN − and Cl − were generated and optimized by density functional theory (DFT) at the B3-LYP/6-311++G(d,p) level. The cluster hydration energy was lower for SCN − than for Cl −. The total Gibbs free energies of hydration of the ions were estimated by a hybrid supermolecule-continuum approach based on DFT. The calculated hydration energies also led to the conclusion that SCN − is less efficiently solvated than Cl −. Due to the easier removal of the hydration shell of SCN − relative to Cl −, SCN − is favored in going across the membrane, giving rise to the protonophoric activity.

CD97, but not its closely related EGF-TM7 family member EMR2, is expressed on gastric, pancreatic, and esophageal carcinomas.

CD97 expression is related closely to the dedifferentiation and tumor stage in thyroid carcinomas. We systematically examined the role of CD97 and its closest relative, EMR2, in normal and malignant gastric, esophageal, and pancreatic tissue. The normal tissues were EMR2-, whereas CD97 was expressed slightly in the parietal cells of gastric mucosa and in exocrine pancreatic cells. Interestingly, intralobular and interlobular pancreatic ducts were CD97+. All tumors were EMR2-. CD97 was expressed by 44 of 50 gastric, 14 of 18 pancreatic, and 10 of 13 esophageal carcinomas. Of the 44 gastric cancers, 27 showed disseminated or scattered tumor cells at the invasion front with stronger CD97 expression than tumor cells located in solid tumor formations. There was no correlation between CD97 levels in the tumors or soluble CD97 in the serum samples and the clinicopathologic features of the patients. Taken together, significant numbers of gastric, esophageal, and pancreatic carcinomas are CD97+, whereas its homolog, EMR2, does not have any role in such tumors.

Laparoscopic management of Meckel’s diverticulum

el’s diverticulum. Technetium has a high affinity for parietal cells of gastric mucosa. Because 95% of Meckel’s diverticulum contains ectopic gastric mucosa, this scan theoretically should identify most of Meckel’s diverticula. Accordingly, the sensitivity, specificity, and overall diagnostic accuracy of the scan is 80 %t o85% ,95% ,an d90% ,respectively. 2 Th efalse-negative rate is 1.7%, whereas the false-positive rate is only 0.05%, because of the abnormal accumulation of isotopes seen in intestinal duplications, Barrett’s esophagus, ulcers, inflammatory bowel disease, intussusception, arteriovenous malformations, an dneoplasm. 3 Patient swit hpersisten tgastrointestina lbleeding requiring multiple transfusions, whose source is unidentified by routine upper and lower endoscopy, angiography, and 99m Tc-pertechnetate scanning, must eventually undergo an abdominal exploration, often with endoscopic assistance; these patients usually have a midgut source, such as a Meckel’s diverticulum, small bowel stromal tumor, or arteriovenous malformation. Obviously, patients with a positive lesion on the 99m Tc-pertechnetate scan must undergo an abdominal exploration to remove the possible Meckel’s diverticulum. In both situations, the initial operative approach may be either laparoscopic or laparotomy, depending on a number of patient and physician factors.

Analysis of human sodium iodide symporter immunoreactivity in human exocrine glands.

The human sodium iodide symporter (hNIS) is an intrinsic transmembrane protein that mediates the active transport of iodide across the basolateral membrane of thyroid follicular cells. In addition to normally functioning thyroid tissue, various extrathyroidal tissues, including salivary gland, lacrimal gland, gastric mucosa, choroid plexus, and lactating mammary gland, have been demonstrated to accumulate iodide. After cloning and molecular characterization of the sodium iodide symporter, expression of hNIS messenger ribonucleic acid has been detected in a broad range of extrathyroidal tissues using Northern blot analysis and RT-PCR. In this study we used both monoclonal and polyclonal antibodies directed against different portions of hNIS protein together with a highly sensitive immunostaining technique to assess hNIS protein expression in tissue sections derived from normal human salivary and lacrimal glands, pancreas, as well as gastric and colonic mucosa. Immunohistochemical analysis of normal human salivary and lacrimal glands revealed marked hNIS immunoreactivity in ductal cells and less intense staining of acinar cells. Further, immunostaining of gastric and colonic mucosa showed marked hNIS immunoreactivity confined to chief and parietal cells in gastric mucosa and to epithelial cells lining mucosal crypts in colonic mucosa. In normal human pancreas, hNIS immunoreactivity was located in ductal cells, exocrine parenchymal cells, and Langerhans islet cells. In conclusion, our study demonstrates the expression of hNIS protein by several human exocrine glands, suggesting that iodide transport in these glands is a specific property conferred by the expression of hNIS protein, which may serve important functions by concentrating iodine in glandular secretions.

Androgen biosynthesis in the stomach: expression of cytochrome P450 17 alpha-hydroxylase/17,20-lyase messenger ribonucleic acid and protein, and metabolism of pregnenolone and progesterone by parietal cells of the rat gastric mucosa.

Dehydroepiandrosterone (DHEA) and its conjugates persist in the rat brain, for up to 1 month after ablation of both adrenals and gonads. Since DHEA synthesis in brain from pregnenolone (PREG) was excluded, we have considered other tissular sources including the digestive tract. In situ hybridization with specific oligonucleotide probes showed that the parietal cells of the gastric mucosa, contrary to other cell types, strongly expressed P450(17) alpha messenger RNA. Expression of the enzyme in the parietal cells was confirmed by immunocytochemistry with specific antibodies. An intense reaction was observed in the stomach of adult males and of cyclic or pregnant females. Access to food did not influence the intensity of immunostaining. It appeared at postnatal days 16-21, then the number of positive cells increased rapidly and leveled off at adult age. Parietal cells were released by pronase digestion of everted stomachs from adult male and female rats and were purified by density gradient centrifugation on Nycodenz. 5 x 10(4) to 1.6 x 10(6) cells were incubated with either 1 microM 14C-PREG or 14C-progesterone (14C-PROG) at 37 C under 95% O2-5% CO2, for 10-180 min. PREG was converted to 17-OH PREG and to androstenediol, whereas PROG was converted to 17-OH PROG and to testosterone. Only minute amounts of either DHEA or androstenedione, respectively, were detected at any incubation time, indicating their fast conversion to the corresponding 17 beta-hydroxysteroids. 3H-25-OH cholesterol was not metabolized to 3H-PREG, and 14C-PREG was not converted to 14C-PROG, in accordance with negative immunocytochemical results with antibodies to cytochrome P450scc and 3 beta-hydroxysteroid dehydrogenase delta 5-->4-isomerase (3 beta-HSD). In conclusion, the parietal cells, which are known as the source of gastric acid secretion, can synthesize testosterone from PROG and androstenediol from PREG. The physiological relevance of such conversions remains to be established.

Ultrastructural and cytochemical analysis of Na+, K+, ATPase and H+, K+, ATPase in parietal cells of gastric mucosa in the rabbit.

Rabbit gastric secretion has the physiological peculiarity of being continuous and uninfluenced by food intake. In this respect, ultrastructural analysis of rabbit parietal cells has revealed morphofunctional features situated between states of rest and very active acid secretion. Our cytochemical study shows that Mg2+ ATPase and ADPase activities vary from cell to cell and can even be totally absent. These activities concern either microcanaliculi or laterobasal folds or both, but never tubulovesicles. Application of the technique of Mayahara to K+ pNPP, associated or not with inhibitors (ouabain, vanadate, N-ethyl-maleimide, sodium fluoride), enabled us to confirm the coexistence of H+, K+, ATPase and Na+, K+, ATPase activities in the rabbit and to determine that these activities concern basolateral folds, microcanaliculi, hyaloplasm and tubulovesicles. The global activity of K+, pNPPase varied considerably in intensity. The results of using inhibitors suggest that proton transport ceases completely in certain cells. The signs of functional alternation found in this study are in agreement with physiological data relative to this animal.

Parietal cell volume, hypergastrinemia, and gastric acid hypersecretion after small bowel resection: Experimental study

One hundred fifty male Sprague-Dawley rats were divided into six groups: control, antrectomy, truncal vagotomy with pyloroplasty, intestinal resection, antrectomy with intestinal resection, and truncal vagotomy with pyloroplasty and intestinal resection. In the control group gastric acid secretion and plasma levels of gastrin were calculated. In the other five groups the same calculations were made 3 months after the corresponding operations. In all animals samples of the gastric wall were taken after specific dyeing of the parietal cells of these samples. In all samples prepared in this way, the variables of parietal cell volume per unit of muscularis mucosa were obtained by a morphometric method. The statistical survey using the levels of gastric acidity, gastrinemia, and parietal volumes of the six groups of animals showed that there is no relation between gastrinemia and gastric acid secretion, nor between gastrinemia and parietal volume, but that there is a significant correlation between gastric acid secretion and parietal volume. Those results suggest that the parietal cell volume in the rat decreases when the secreting capacity of the mucosa is decreased, and that the plasma levels of gastrin do not have a direct trophic effect on the parietal cells of gastric mucosa.

COEXISTENCE OF PRIMARY OVARIAN INSUFFICIENCY, PRIMARY ADRENOCORTICAL INSUFFICIENCY AND IDIOPATHIC HYPOPARATHYROIDISM

ABSTRACT A patient is described who developed idiopathic hypoparathyroidism at age 3, primary ovarian failure at age 15, and primary adrenocortical failure at age 17. The primary nature of the ovarian insufficiency is indicated by the finding on several occasions of elevated urinary gonadotropin. The diagnosis of primary hypoadrenalism is based on absence of a rise in urinary 17-hydroxycorticoid excretion after 5 days of ACTH administration, and has been confirmed by the finding of elevated plasma ACTH. The combination of gonadal, adrenocortical and parathyroid failure has not been described previously. Antibodies to adrenal cortex, to thyroid antigens and to parietal cells of gastric mucosa have been demonstrated in the patient's plasma. It is postulated that the multiple glandular failure is the consequence of an auto-immune process.

Influence of Hypophysectomy on Oxidative Enzymes and Size of Parietal Cells in Gastric Mucosa.

SummaryGastric parietal cells were reduced in size after hypophysectomy of the rat. Treatment with STC enlarged the cells but did not restore their normal size. Histochemical demonstration of cytochrome c oxidase, DPN diaphorase and 5 dehydrogenases did not reveal any one which was affected more than the others in either parietal or chief cells. In both cell types some overall reduction in activity occurred coincident with a reduction in cell size.