Distribution of lectin-binding sites in oxyntic and chief cells of isolated rabbit gastric glands

Cathartocytosis: How Cells Jettison Unwanted Material as They Reprogram

Injury can cause differentiated cells to undergo massive reprogramming to become proliferative to repair tissue via a cellular program called paligenosis. Gastric digestive-enzyme-secreting chief cells use paligenosis to reprogram into progenitor-like Spasmolytic-Polypeptide Expressing Metaplasia (SPEM) cells. Stage 1 of paligenosis is to downscale mature cell architecture via a process involving lysosomes. Here, we noticed that sulfated glycoproteins (which are metaplasia and cancer markers in mice and humans) were not digested during paligenosis but excreted into the gland lumen. Various genetic and pharmacological approaches showed that endoplasmic reticulum membranes and secretory granule cargo were also excreted and that the process proceeded in parallel with, but was independent lysosomal activity. 3-dimensional light and electron-microscopy demonstrated that excretion occurred via unique, complex, multi-chambered invaginations of the apical plasma membrane. As this lysosome-independent cell cleansing process does not seem to have been priorly described, we termed it "cathartocytosis". Cathartocytosis allows a cell to rapidly eject excess material (likely in times of extreme stress such as are induced by paligenosis) without waiting for autophagic and lysosomal digestion. We speculate the ejection of sulfated glycoproteins (likely mucins) would aid in downscaling and might also help bind and flush pathogens (like H pylori which causes SPEM) away from tissue.

Light and electron microscopic investigation of the lectin-binding pattern in the oxyntic gland region of bovine abomasum

For the first time the expression of glycoconjugate residues in the oxyntic gland region of bovine abomasum has been investigated by means of lectin histochemistry. For light microscopic investigations, a battery of ten lectins, Con A, PSA, UEA I, WGA, LEA, SNA, RCA120, MPA, DBA and SBA was used. For electron microscopic examinations, WGA and RCA120 were utilized. The staining pattern of the lectins in all exocrine cell types of the oxyntic gland region is described. Compared to the results of monogastric species our study reveals some similarities, but just as many differences in the composition of glycoconjugate residues in bovine exocrine cell types. Typical for surface mucous cells is the amount of L-fucose, N-acetyl glucosamine residues and Galbeta1, 4GlcNAc sequences in the secretory granules. SNA could serve as a marker for surface mucous cells, because this lectin exclusively stains the plasma membrane and the secretory granules of surface mucous cells and the extracellular mucus. L-fucose and N-acetyl glucosamine are typical for the secretory granules of mucous neck cells. In addition, the secretory granules show the highest amount of N-acetyl galactosamine residues of all exocrine cells, so that DBA and SBA are recommended as marker lectins for mucous neck cells. Most lectins strongly stain the intracellular membrane system of oxyntic cells. The cocktail of glycoconjugates in the vicinity of the HCI production site provide protection against chemical injury. In chief cells only the apical plasma membrane is more or less labeled with all lectins apart from SNA. Specific marker lectins for oxyntic cells or chief cells of the bovine have not been characterized.

Effect of proton pump inhibitor, omeprazole, on expression of rat parietal cell specific carbohydrate antigen, type 2 chain N-acetyllactosamine

The effect of a proton pump inhibitor, omeprazole, on the rat gastric mucosal expression of carbohydrate antigens was studied. Type 2 chain N-acetyllactosamine was detected specifically on the apicocanalicular cell membranes of parietal cells. Pretreatment of rats with omeprazole profoundly suppressed the antigen expression, which followed the inhibition of gastric acid secretion. When omeprazole was discontinued, the antigen was reexpressed, which preceded the restoration of acid secretion. The antigen-negative tissues became antigen-positive when they were desialylated. Gastric membrane vesicles from the normal and omeprazole-treated rats were antigen-positive and -negative, respectively. SDS-PAGE revealed that a glycoprotein with an apparent molecular weight of 64-78 kDa carried type 2 chain N-acetyllactosamine. In the omeprazole-treated rats, the same molecular weight glycoprotein was positively immunostained only after desialylation. We concluded that: (1) the expression of type 2 chain N-acetyllactosamine was closely correlated with gastric acid secretion, and (2) the inhibition of acid secretion was accompanied by the sialylation of the parietal cell membrane glycoprotein.

Histamine-induced chloride channels in apical membrane of isolated rabbit parietal cells

The electrical properties of the apical membrane of isolated rabbit parietal cells were studied using the patch-clamp technique. The apical membrane of the parietal cells plated on Matrigel and maintained in culture conditions was identified by lectin-binding studies. Cell-attached and excised inside-out patches from 10(-4) M cimetidine-treated parietal cells infrequently contained Cl- channels (9% of the patches). A single class of voltage-dependent outwardly rectifying Cl- channels with 24 +/- 1-pS conductance was observed in 75% of the patches from cells stimulated (acid secreting) by 10(-4) M histamine. Other anions passed through these channels with a permeability sequence of I- (1.2) greater than Br- (1.1) greater than or equal to Cl- (1.0) greater than NO3- (0.7) greater than SO4(2-) (0.1), but there was a very low permeability for Na+ or K+ (PCl-/PNa+ or PCl-/PK+ greater than 5). In inside-out patch configurations the Cl- channel was insensitive to Ba2+ and stilbene derivatives but was inhibited by diphenylamine-2-carboxylic acid in a manner characteristic of a reversible open-channel blocker. It is concluded that H2-receptor agonist stimulation of acid secretion by rabbit parietal cells activates Cl- channels in the apical cell membrane.

Isolation and characterization of gastric microsomal glycoproteins. Evidence for a glycosylated beta-subunit of the H+/K(+)-ATPase

Detergent-solubilization of hog gastric microsomal membrane proteins followed by affinity chromatography using wheat germ agglutinin or Ricinus communis I agglutinin resulted in the isolation of five glycoproteins with the apparent molecular masses on sodium dodecyl sulfate polyacrylamide gels of (in kDa): 60-80 (two glycoproteins sharing this molecular mass); 125-150; and 190-210. In the nonionic detergent Nonidet P-40 (NP-40), the 94 kDa H+/K(+)-ATPase was recovered exclusively in the lectin-binding fraction; however, in the cationic detergent dodecyltrimethylammonium bromide, most of the ATPase was recovered in the nonbinding fraction. Detection of glycoproteins either by periodic acid-dansyl hydrazine staining of carbohydrate in polyacrylamide gels or by Western blots probed with lectins indicated that the majority of the ATPase molecules are not glycosylated. In addition, in the absence of microsomal glycoproteins, the NP-40-solubilized ATPase does not bind to a lectin column. Taken together, these results suggest that the recovery of NP-40-solubilized ATPase in the lectin-binding fraction is due to its noncovalent interaction with a gastric microsomal glycoprotein. Immunoprecipitation of the ATPase from NP-40-solubilized microsomal membrane proteins resulted in the co-precipitation of a single 60-80 kDa glycoprotein. Characterization of the 60-80 kDa glycoprotein associated with the ATPase revealed that: it is a transmembrane protein; it has an apparent core molecular mass of 32 kDa; and, it has five asparagine-linked oligosaccharide chains. Given its similarity to the glycosylated beta-subunit of the Na+/K(+)-ATPase, this 60-80 kDa gastric microsomal glycoprotein is suggested to be a beta-subunit of the H+/K(+)-ATPase.