Analysis of Flow Phenomena in Gastric Contents Induced by Human Gastric Peristalsis Using CFD

This paper uses computational fluid dynamics to simulate and analyze intragastric fluid motions induced by human peristalsis. We created a two-dimensional computational domain of the distal stomach where peristalsis occurs. The motion of the gastric walls induced by an antral contraction wave (ACW) on the wall of the computational domain was well simulated using a function defined in this study. Retropulsive flow caused by ACW was observed near the occluded region, reaching its highest velocity of approximately 12 mm/s in the narrowest region. The viscosity of the model gastric contents applied in this study hardly affected the highest velocity, but greatly affected the velocity profile in the computational domain. The shear rate due to gastric fluid motion was calculated using the numerical output data. The shear rate reached relatively high values of approximately 20 s⁻¹ in the most occluded region. The shear rate profile was almost independent of the fluid viscosity. We also simulated mass transfer of a gastric digestive enzyme (pepsin) in model gastric content when peristalsis occurs on the gastric walls. The visualized simulation results suggest that gastric peristalsis is capable of efficiently mixing pepsin secreted from the gastric walls with an intragastric fluid.     

Crystal structure of human PACRG in complex with MEIG1 reveals roles in axoneme formation and tubulin binding

1. Download : Download high-res image (220KB)
2. Download : Download full-size image

     

Electron paramagnetic resonance study of ferrous cytochrome P-450scc-nitric oxide complexes: effects of cholesterol and its analogues

Electron paramagnetic resonance (EPR) spectra of nitric oxide (NO) complexes of ferrous cytochrome P-450scc were measured at 77 K for the first time without using the rapid-mixing and freeze-quenching technique. Without substrate the EPR spectra were very similar to those of cytochrome P-450cam (from Pseudomonas putida) and cytochrome P-450LM (from rat liver microsomes) with rhombic symmetry; gx = 2.071, gz = 2.001, gy = 1.962, and Az = 2.2 mT for 14NO complexes. Upon addition of substrates [such as cholesterol, 22(S)-hydroxycholesterol, 22(R)-hydroxycholesterol, 25-hydroxycholesterol, and 22-ketocholesterol], the EPR spectra exhibited many variations having rhombic symmetry in the major component and an additional minor component with less rhombic symmetry. Furthermore, addition of 20(S)-hydroxycholesterol caused a striking change in the EPR spectrum. The component with rhombic symmetry disappeared completely, and the component with less rhombic symmetry dominated (gx = 2.027, gz = 2.007, gy = 1.984, and Az = 1.76 mT for 14NO complexes). These observations suggest the existence of the following physiologically important natures: (1) the conformational flexibility of the active site of the enzyme due to the steric interaction between the substrate and the heme-bound ligand molecule and (2) the importance of the hydroxylation of the cholesterol side chain at the 20S position to proceed the side-chain cleavage reaction in cytochrome P-450scc.     

Aggregatibacter actinomycetemcomitans induces detachment and death of human gingival epithelial cells and fibroblasts via elastase release following leukotoxin‐dependent neutrophil lysis

Aggregatibacter actinomycetemcomitans is considered to be associated with periodontitis. Leukotoxin (LtxA), which destroys leukocytes in humans, is one of this bacterium's major virulence factors. Amounts of neutrophil elastase (NE), which is normally localized in the cytoplasm of neutrophils, are reportedly increased in the saliva of patients with periodontitis. However, the mechanism by which NE is released from human neutrophils and the role of NE in periodontitis is unclear. In the present study, it was hypothesized that LtxA induces NE release from human neutrophils, which subsequently causes the breakdown of periodontal tissues. LtxA‐treatment did not induce significant cytotoxicity against human gingival epithelial cells (HGECs) or human gingival fibroblasts (HGFs). However, it did induce significant cytotoxicity against human neutrophils, leading to NE release. Furthermore, NE and the supernatant from LtxA‐treated human neutrophils induced detachment and death of HGECs and HGFs, these effects being inhibited by administration of an NE inhibitor, sivelestat. The present results suggest that LtxA mediates human neutrophil lysis and induces the subsequent release of NE, which eventually results in detachment and death of HGECs and HGFs. Thus, LtxA‐induced release of NE could cause breakdown of periodontal tissue and thereby exacerbate periodontitis.     

Existence of multiple forms of cytochrome P-450scc purified from bovine adrenocortical mitochondria

Three fractions of cytochrome P-450scc (denoted as fractions a, b, and c) were purified by a new procedure from bovine adrenocortical mitochondria. The amino-acid content analyses of these three fractions showed no difference. NH2-terminal amino-acid sequences of cytochrome P-450scc fractions, a and b agreed completely with the sequence deduced by nucleotide sequence of cDNA of cytochrome P-450scc mRNA (Morohashi, K., Fujii-Kuriyama, Y., Okada, Y., Sogawa, K., Hirose, T., Inayama, S. and Omura, T. (1984) Proc. Natl. Acad. Sci. USA 81, 4647-4651), whereas the sequence of fraction c showed a missing of isoleucine at the NH2-terminal. COOH-terminal ámino-acid sequences of fractions a, b and c were -Gln-Ala-COOH, identical with the deduced sequence from the cDNA. Measurements of the enzymatic activities of cholesterol side-chain cleavage reaction revealed no distinct difference among these three fractions. Although each of these fractions appeared as a single protein staining band upon SDS-polyacrylamide gel electrophoresis, these fractions showed heterogeneities upon two-dimensional electrophoresis and chromatofocusing. Fraction a contained the major form of cytochrome P-450scc, and its isoelectric point was estimated to be pH 7.8 by isoelectric focusing under both native and denatured conditions, and this value was confirmed by chromatofocusing. Neither of the carbohydrate-specific stainings (such as periodic acid-Schiff staining and lectin-peroxidase stainings using concanavalin A, wheat-germ agglutinin, and soybean agglutinin) of purified cytochrome P-450scc fractions after the electrophoretic resolution on SDS-polyacrylamide gel could show cytochrome P-450scc fractions as glycoproteins, suggesting that the heterogeneities were not due to the glycosylation state.     

Induction of histidine decarboxylase by dexamethasone in mastocytoma P-815 cells

Dexamethasone at a concentration as low as 10 nM significantly increased both the histamine content and histidine decarboxylase activity of cultured mastocytoma P-815 cells. Both effects were clearly seen using several glucocorticoids, which were as effective as dexamethasone. In contrast to that of histamine, the serotonin level of mastocytoma P-815 cells was decreased by treatment with dexamethasone. The dexamethasone-induced increases in histamine content and histidine decarboxylase activity were completely suppressed by the addition of cycloheximide and actinomycin D. Mastocytoma P-815 cells were found to possess binding sites for [3H]dexamethasone in the cytosol (Kd = 15.7 nM) and the nuclei (Kd = 1.26 nM). These results show that glucocorticoids significantly stimulate de novo synthesis of histidine decarboxylase.     

Electrophoretic Studies on Plant Protoplasts I. pH Dependence of Zeta Potentials of Protoplasts from Various Sources

Electrophoretic mobilities of plant protoplasts from varioussources were measured, as a function of the pH of the medium,by a micro-electrophoresis technique to characterize the protoplastsin terms of curves of zeta potential vs. protoplast surfacepH (pH_s). The shape of the curves of zeta potential vs. pH_scurves differed among preparations of protoplasts isolated fromvarious species and strains. The isoelectric points (pI) ofthe protoplasts measured in this study were between 3.0 and4.0. These differences among the protoplasts suggest that itmay be possible to develop an electrophoretic method for theselection of protoplasts. The shape of the curves of zeta potentialvs. pH_s also indicated that carboxyl groups, as well as phosphategroups, may contribute to the negative charges on the surfaceof protoplasts. (Received October 14, 1988; Accepted February 22, 1989)     

Prostaglandin D2 receptor of mastocytoma P-815 cells--possible regulation by phosphorylation and dephosphorylation

The 3H-labeled prostaglandin D2 [( 3H]PGD2) binding protein in the membrane fraction of mastocytoma P-815 cells was characterized. The specific binding of [3H]PGD2 to the cells or the membranes reached a maximum at pH 5.6, and was saturable, displaceable and of high affinity when incubated at 0 or 37 degrees C. The Bmax values for [3H]PGD2 binding in the two preparations at pH 5.6 were much higher at 0 degrees C than at 37 degrees C, whereas the Kd values were almost equal (85.3 nM for the cells and 80.5 nM for the membranes, respectively). High specific [3H]PGD2 binding activity in the mildly acid-treated cells was still observed when the external pH was raised from 5.6 to 7.2. Furthermore, specific [3H]PGD2 binding to the membranes (at 0 degrees C, pH 5.6) increased on addition of phosphatase inhibitors (NaF and molybdate) in the presence of 10 microM ATP, but practically disappeared on pretreatment of the membranes with phosphatase. On incubation of the membrane with [gamma-32P]ATP and molybdate, the stimulated incorporation of the [32P]phosphate into several peptides, including ones having an Mr of around 100,000-120,000, was observed. These results suggest that [3H]PGD2 binding in the mastocytoma P-815 cell membrane is controlled through phosphorylation-dephosphorylation of the receptor itself.     

Scale Arrangement Pattern in a Lepidopteran Wing. 1. Periodic Cellular Pattern in the Pupal Wing of Pieris rapae

In most species of lepidopteran insects, anteroposterior rows formed by scales are arranged at regular intervals in the adult wing; within each row two kinds of scales are alternately arranged. To investigate the cellular basis for the scale arrangement pattern, we examined cell arrangement in the epidermal monolayer of the pupal wing of a small white cabbage butterfly, Pieris rapae , by scanning electron microscopy and light microscopy.
The arrangement of scale precursor cells, closely resembling that of scales in the adult wing, was observed in the wing epidermis of the early pupa. Scale precursor cells are proximodistally elongated and form anteroposterior rows. Within a row two kinds of scale precursor cells are nearly alternately arranged, which is not so precise as the alternation of scales in the adult wing. Individual rows of scale precursor cells are separated by rows of single or double undifferentiated general epidermal cells. Occasionally, arrangement abnormalities occur both in the adult and the pupal wing. The cellular basis for the regular spacing of scale rows is discussed.