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H Showell

Publications and source records attributed to H Showell.

7 recordsLinked to original sources
PubMed1990

A factor in serum lowers resistance and opens tight junctions of MDCK cells.

During an inflammatory reaction, factors in blood affect the permeability of endothelium and possibly organ epithelium. In this study we partially characterized a factor in human and canine blood that lowered the transepithelial electrical resistance (TER) of canine kidney epithelial cells (MDCK) and examined whether vascular permeability factors [complement component C3a and C5a and platelet-activating factor (PAF)] were responsible for this reaction. C3a and C5a caused a small (10-13%) dose-related decrease in the TER (alpha = 0.05), whereas PAF had no effect. In contrast, the factor found in both serum and plasma caused a large (60-83%) dose-dependent decrease (saturated at 30%) in the TER that was reversible within 60 min. The blood factor, which does not appear to be albumin, was heat stable and has an apparent molecular mass of 67 kDa. It preferentially decreased the TER of the epithelium when it came in contact with its basolateral surface and significantly lowered the resistance within 60 min by opening the zonula occludentes. These findings suggest that C3a, C5a, and a factor in blood can directly modulate the permeability of renal epithelium.

Animals↗
PubMed1984

Structural requirements for formyl homooligopeptide chemoattractants.

Using solution peptide synthesis, we have made three series of N alpha-formylated homooligopeptides, from the dipeptide to the heptapeptide, derived from L-methionine, L-norleucine, and S-methyl-L-cysteine and related to the chemotactic peptide N alpha-formylmethionylleucylphenylalanine. Compounds were prepared to determine the combined effects of the main-chain length and the presence of a sulfur atom in side-chain gamma- and delta-positions. Each peptide was tested for its ability to induce rabbit peritoneal polymorphonuclear leukocytes in the presence of cytochalasin B to secrete granule enzymes. In parallel, a conformational analysis was carried out in the solid state and in solution, using infrared absorption and circular dichroism. We examined these peptides in solvents of widely different polarities, i.e., chloroform, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoropropan-2-ol, and mixed organic-aqueous media. The tendencies to form antiparallel-chain beta-associated and folded structures were determined. The biological and conformational data are described in terms of a model of the chemotactic peptide receptor of rabbit neutrophils recently proposed by Freer et al. (1982) [Freer, R.J., Day, A.R., Muthukumarswamy, N., Pinon, D., Wu, A., Showell, H.J., & Becker, E.L. (1982) Biochemistry 21, 257-263]. In the three N alpha-formylated C-methoxy homooligopeptide series tested, the highest level of activity attained is at the tetrapeptide or pentapeptide stage, confirming the suggestion that the formylpeptide receptor is large enough to accommodate a peptide with at least four amino acid residues.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Purification of human C5a des arg by immunoadsorbent and molecular sieve chromatography.

Human C5a des arg was isolated from complement-activated serum by immunoadsorption followed by Sephadex G-75 chromatography. C5a des arg obtained by this 2-step procedure was shown to be immunologically identical to C5a des arg purified by a conventional multi-step method, homogeneous on SDS-polyacrylamide gels, and biologically active. Although this technique yields approximately the same amount of C5a des arg/liter of activated serum as that obtained by conventional methods, its simplicity and relative rapidity make it a practical alternative.

Animals↗
PubMed1979

Acute inflammatory pulmonary reactions induced by chemotactic factors.

Acute inflammatory reactions have been produced in hamster lungs by the intrapulmonary instillation of preformed chemotactic mediators (C5fr and F-Met-Leu-Phe). By the use of 111Indium and 125Iodine labeling of homologous neutrophils (PMNs) and homologous albumin, respectively, it has been possible to obtain highly reproducible and quantitative parameters of the acute inflammatory response. The lung responds in a dose-dependent and time-dependent manner to the instillation of preformed chemotactic mediators. The quantitative parameters indicative of PMN influx were more prominent than changes in vascular permeability. The data obtained by the use of radiolabeled PMNs were confirmed by observation with light microscopy. Nonchemotactic substances such as human IgG, serum albumin, and C4 failed to induce inflammatory responses in lung. Interestingly, intact C5 instilled into lung was extremely phlogistic, apparently due to hydrolysis once within the lung. These studies provide an approach to reliable quantitative parameters of inflammatory reactions in the lung and emphasize the in vivo biologic effects of chemotactic mediators.

Animals↗
PubMed1979

Preservation of C3, C5, and C5a functional activities by a new radiolabeling method; demonstration of C5 products in complement-activated serum.

A new method is described for the radiolabeling of C3, C5, and C5a. Using a methylation procedure we have labeled C3, C5, and C5a with 14CH20, achieving high specific activity, without loss of hemolytic activity in the case of C3 and C5, and in the case of C5a, full retention of chemotactic and enzyme releasing activities. The distribution of radiolabel in the alpha and beta chains of C5 was 75 and 25%, respectively. Using intact labeled C5 the fragmentation pattern in zymosan-activated human serum, assessed by gel filtration and electrophoresis, is complex, yielding multiple fragmentation products. The labeling method described in this paper yield materials that have many advantages over the currently used labeling procedures.

Autoradiography↗