Up- and down-regulation of membrane receptors as possible mechanisms related to the antiulcer actions of milk in rat gastric mucosa

The effects of a cow's milk diet on receptor activity and histamine metabolism in gastric glands and mucosa isolated from adult rats were examined. The milk diet was associated with (1) a decreased mobilization of H₂ receptors by histamine and (2) an increased mobilization of PGE₂ (prostaglandin E₂) receptors in mucous cells (cytoprotective effect) and parietal cells (antiacid effect). These changes are not observed for the receptors reducing pentagastrin- and histamine-induced gastric acid secretion (pancreatic/enteroglucagons, somatostatin) and stimulating mucus, bicarbonate and pepsin secretions in the rat (secretin). Cimetidine produced a parallel displacement of the histamine dose-response curve, suggesting competitive inhibition between this classical H₂ receptor antagonist and histamine in the two experimental groups. Prostaglandins and other components in milk such as EGF (epidermal growth factor) and somatostatin might therefore protect gastric mucosa by a differential control of PGE₂ and histamine H₂ receptor activity eitherdirectly (PGE₂ in milk) orindirectly (inhibition of endogeneous histamine synthesis/release and stimulation of PGE-I synthesis/release).     

Increase in cytoplasmic calcium content in internodal cells of Lamprothamnium upon hypotonic treatment

Abstract Internodal cells of Lamprothamnium succinctum, a brackish water Characeae, regulate turgor pressure in response to changes in external osmotic pressure (turgor regulation). When internodal cells were transferred to a hypotonic medium containing 3.9 mol m^?3 Ca²⁺, the cell osmotic pressure decreased and the original turgor pressure was recovered. During turgor regulation Ca content of the cytoplasm increased significantly. Lowering the external Ca²⁺ concentration from 3.9 to 0.01 mol m^?3 inhibited this increase in cytoplasmic calcium content. In a hypotonic medium containing 0.01 mol m^?3 Ca²⁺, turgor regulation was inhibited as previously reported (Okazaki & Tazawa, 1986a). Thus transient increase in cytoplasmic Ca, probably in the ionized form, induced by hypotonic treatment may play an important role in turgor regulation.     

In vivo P-31 NMR measurements of phosphate metabolism in Platymonas subcordiformis as related to external pH

The phosphate metabolism of Platymonas subcordiformis was investigated by 31P-NMR spectroscopy with special attention on the effect of external pH. Glycolyzing cells and cells energized by respiration or photosynthesis gave spectra dependent upon their metabolic state. The transition from deenergized to energized states is accompanied by a shift of cytoplasmic pH from 7.1–7.4, an increase of ATP level and-in well energized cells-the appearance of a new signal tentatively assigned to phosphoarginine.The spectra remain stable over a wide range of external pH. Cytoplasmic pH is well regulated in respiring cells for external pH in the range 5.3–12.3. The typical 0.4 units difference of internal pH in energized as compared to deenergized cells is not affected by external pH in the range 6–12. The intensity of a signal attributed to PEP is markedly increased at high external pH. pH regulation is less efficient below external pH of 6 in deenergized cells. Below pH 3.8 oxidative phosphorylation ceases. Upon raising cytoplasmic pH to 7.4 in deenergized cells polyphosphate chains start to disintegrate.Abbreviations PEP Phosphoenolpyruyate - P _i inorganic phosphate - PP _i inorganic pyrophosphate - poly P polyphosphates - PP-1, PP-2, PP-3 terminal, second, and third phosphate residue of polyphosphates - PP-4 core phosphate residues of polyphosphates - pH _i , pH _o internal (cytoplasmic) and external pH - NTP/NDP nucleotide triphosphate/-diphosphate - S/N signal to noise ratio     

Postnatal D2-CAM/N-CAM Sialylation State Is Controlled by a Developmentally Regulated Golgi Sialyltransferase

Abstract: Golgi-enriched fractions have been isolated from rat brain of increasing postnatal age and defined by electron microscopy and distribution of marker enzymes. The expression of sialyltransferase activity associated with these fractions has been demonstrated to developmentally decrease and this appeared to be, in part, dependent on endogenous competitive inhibition. The developmental regulation of this activity paralleled the sialylation state of the neural cell adhesion molecule (D2-CAM/N-CAM) and could be demonstrated to be capable of endogenously sialylating this protein in the isolated Golgi fractions. In 12-day-old animals the majority of the transferred [¹⁴C]sialic acid was found to be associated with the high-molecular-weight [>200 kilodaltons (kd)] form of D2-CAM/N-CAM, indicative of the protein having been heavily sialylated. Sialylation of the individual D2-CAM/N-CAM polypeptides was also demonstrated in both 12-day and adult animals and transfer was evident only in the 180-kd and 115-kd components and not in the 140-kd component. In contrast, Golgi-enriched fractions prepared from adult animals showed little capability of heavily sialylating D2-CAM/N-CAM to any significant extent.     

In addition to the ARS core, the ARS box is necessary for autonomously replicating sequences

Summary Autonomously replicating sequences (ARSs) were cloned from nuclear and mitochondrial DNA of D. melanogaster using YIp5, which is composed of pBR322 and the yeast ura3 gene, as the cloning vector and YNN27, a Ura^- yeast strain as the recipient. The nucleotide sequences of six ARSs, two from nuclear bulk, two from the nuclear 1.688 satellite, and two from mitochondorial DNA, were determined. The relationship between the transformation frequency and the inclusion of the ARS core, 5 _T ^A TT-TAT _A ^G TTT _T ^A 3, of these fragments was analysed. All the ARSs contained an ARS core or a single base change of it. However, not all the fragments that contained a single base change of the ARS core were able to transform the recipient cells, suggesting that certain bases in the ARS core were not exchangeable. It is suggested by transformation experiments with subfragments that in addition to an ARS core, an ARS box which is located within 25 bp upstream of the ARS core and whose sequence is composed of 5TNT _G ^A AA 3, is necessary for autonomous replication.     

Integrated regulation of the photosynthetic gene family from Arabidopsis thaliana in transformed tobacco cells

Summary Expression of the three chlorophyll a/b binding protein (cab) genes of Arabidopsis thaliana was studied in transformed tobacco tissues. For each cab gene, approximately 1000 bp of the promoter region plus a portion of the structural gene was inserted into a promoter-expression vector such that a translational fusion between the cab gene and the promoter-less chloramphenicol acetyltransferase (cat) gene was formed. The constructed molecules were introduced into either cultured tobacco cells or tobacco leaves and the promoter activity was monitored as chloramphenicol acetyltransferase activity. The light-grown tissues exhibited 1.5- to 60-fold greater promoter activity than did dark-grown tissues. Expression of the cab promoters was tissue specific: activities were much stronger in green leaves than other tissues. The cab promoters were almost equally active in transformed calli or shoots derived from leaves. However, in cultured tobacco cells, one promoter was two to three times stronger than the other two. The chimeric gene fusion, cab-cat, segregated in the F1 generation as a dominant Mendelian trait.