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Biomedical subjects

K E Johnson

Publications and source records attributed to K E Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1983

Acid pH and weak acids induce Na--Cl cotransport in the rabbit urinary bladder.

We have described a coupled Na--Cl entry step at the apical membrane of a tight epithelium, the rabbit urinary bladder. Mucosal pH values, more acid than 4.6, stimulate a 20 to 40-fold increase in mucosal-to-serosal Na+ and Cl- flux. The flux increase is almost completely blocked by low concentrations of of bumetanide. The transepithelial movement of Na+ and Cl- is normally electroneutral; however, when weak acids (such as acetate) are present in the mucosal solution, the acid-induced increase in flux is accompanied by a large increase in short-circuit current. Besides blockage by bumetanide, both the increase in flux and short-circuit current are blocked by: (1) Na+-free solutions on the mucosa; (2) Cl--free solutions on the mucosa; (3) phosphodiesterase inhibitors; (4) ouabain in the serosal solution; (5) K+-free solutions on the serosa; and (6) HCO3--free solutions on the serosa. The increase in the fluxes and the short-circuit current is unaffected by: (1) amiloride application in the mucosal solution; (2) mucosally applied stilbene derivatives which block Cl-/HCO3- exchange (SITS); and (3) Cl--free solutions applied to the serosa. We interpret these results to imply a coupled Na--Cl uptake step at the apical membrane which is stimulated by intracellular acetate (or (pH). The uptake step leads to a movement of Na+ and Cl- across the basolateral membrane, which is mediated by the Na+, K+-ATPase and a Na/Cl/HCO3- exchange mechanism. Our results demonstrate that "tight" epithelia may, under appropriate circumstances, demonstrate mechanisms of ion movement which are similar to "leaky" epithelia.

Acids↗
PubMed1983

Conditioning of a culture substratum by the ectodermal layer promotes attachment and oriented locomotion by amphibian gastrula mesodermal cells.

We have found that ectodermal fragments of Ambystoma maculatum gastrulae deposit immense numbers of 0.1 micron diameter extracellular fibrils on plastic coverslips. When migrating mesodermal cells from A. maculatum gastrulae are seeded on such conditioned plastic substrata, they attach and begin migrating after 15-30 min in vitro. We did a detailed analysis of the relationship between fibril orientation and cell migration using time-lapse cinemicrography, scanning electron microscopy, and a microcomputer with a graphics tablet and morphometric program. We found that cells move in directions closely related to the orientation of fibrils. Usually fibrils are oriented in dense arrays with a predominance of fibrils running parallel to the blastopore-animal pole axis of the explant, and cells move preferentially along lines parallel to the blastopore-animal pole axis. When fibrils are unaligned, cells move at random. We have also shown that cells move with a slightly stronger tendency towards the animal pole direction. These results are discussed concerning the mechanism of specific cell migration during amphibian gastrulation.

Ambystoma↗
PubMed1983

Comparative study of extracellular fibrils on the ectodermal layer in gastrulae of five amphibian species.

Previous studies have shown the presence of a network of extracellular fibrils on the inner surface of the ectodermal layer of the Ambystoma maculatum gastrulae. The alignment of the network along the blastopore-animal pole axis has suggested that the network of fibrils guides the migrating mesodermal cells in gastrulae by contact guidance. We have also shown that these fibrils can be deposited on substrata by explanted embryonic fragments and that substrata conditioned in this manner support directed cell migration. In this study, we found that the appearance of the fibrils in the embryos coincides with the start of cell migration towards the animal pole. Gastrulae of three urodele species examined (A. maculatum, A. mexicanum and Cynops pyrrhogaster) have similar dense networks of fibrils. Xenopus laevis gastrulae also have similar fibrils but fewer fibrils compared to urodele embryos. Rana pipiens gastrulae have very few extracellular fibrils. The scarcity of the fibrils in anuran species may be related to the differences in arrangement of mesodermal cells during migration.

Ambystoma↗
PubMed1983

Campylobacter jejuni enteritis: efficacy of antimicrobial and antimotility drugs.

We analyzed retrospectively the illnesses of 82 patients with Campylobacter jejuni enteritis to ascertain the efficacy of antimicrobials and drugs that inhibit gastrointestinal motility. Forty-four patients were treated with only supportive measures consisting of diet modification and fluids; 22 others received an antimotility agent for at least 48 h; the remaining 16 were given an antimicrobial at or near the time of therapeutic intervention. The three groups were similar in terms of severity of symptoms and signs. There was a greater need for secondary antimicrobial therapy because of static or worsening illness in the group treated with antimotility agents (8/22, 36%) than in the others (4/44,9%; 2/16, 13%: p less than 0.02). Furthermore, six patients treated initially and 10 treated secondarily with erythromycin or tetracycline had illnesses of shorter duration than did untreated controls paired by age, sex, length and severity of symptoms and signs, hematochezia, and antimotility therapy (p less than 0.05). Thus treatment of C. jejuni enteritis with erythromycin or a tetracycline shortened the illness, but antimotility agents impeded the resolution of the infection.

Adolescent↗
PubMed1982

Cell locomotion in vitro by Xenopus laevis gastrula mesodermal cells.

Prospective mesodermal cells of Xenopus laevis gastrulae showed substantial locomotion in vitro, averaging 4.3 microns/min, when dissociated and cultured on a glass surface coated with collagen and fetal bovine serum. The cells translocate by making lamellipodia and filopodia whereas the main cell body remains rounded. When two mesodermal cells made contact with each other, they showed contact paralysis of lamellipodial activity. In contrast, when mesodermal cells contact ectodermal cells, contact paralysis does not occur. Rather, migrating mesodermal cells continue to translocate. The locomotion in vitro appears to mimic that in vivo during gastrulation, because of the similarities of the rate of movement and the cell shape in culture and in embryos. Neither prospective ectodermal cells from gastrulae nor prospective mesodermal cells from blastulae showed locomotion under the same culture conditions.

Animals↗
PubMed1982

Movement and guidance of migrating mesodermal cells in Ambystoma maculatum gastrulae.

A scanning electron microscopic study in early gastrulae of Ambystoma maculatum showed that migrating presumptive mesodermal cells were strongly oriented toward the animal pole. They had lamellipodia and filopodia at their leading edges, and rounded or tapering, tail-like, trailing edges. Of the cells whose polarization could be determined unequivocally, 81% appeared to be directed in a quadrant toward the animal pole, and 93% were directed to some extent away from the blastopore. This strong orientation suggests that specific mechanisms direct cell movement, in addition to the non-specific dispersive mechanism of the contact inhibition of cell movement. There is a network of fine extracellular fibrils that covers the inner surface of the ectodermal layer. Filopodia of the migrating cells frequently attach to and appear to follow the fibrils, suggesting that the fibrils serve as a guiding substratum for cell attachment and movement. There are areas where the fibrils are apparently aligned along the blastopore-animal pole axis, and a preliminary statistical analysis using micrographs at high magnification showed a significant alignment parallel to the blastopore-animal pole axis. This fibril alignment could cause the strong orientation of the mesodermal cells by means of contact guidance.

Ambystoma↗
PubMed1981

Circus movements in dissociated cells in normal and hybrid frog embryos.

Circus movements, involving circumferential rotation of a hyaline cytoplasmic blister and endoplasmic flow, occur in EDTA-dissociated gastrula stage Rana pipiens embryos. Such cell movements occur in very few cells taken from pre-gastrula stage embryos. During gastrulation, there is a progressive increase in the proportion of a population of cells that is engaged in circus movements. Circus movements do not occur in dividing cells. Individual cells in culture, as well as small clusters of cells in vitro, are jostled about in an apparently aimless fashion over short distances by circus movements, although the translocation of masses of cells over long distances is substantially greater than the translocation of isolated cells. In an early gastrula stage normal embryo, cells from around the site of blastopore invagination are most active in circus movements. Cells taken from different stages of arrested hybrid embryos show variable depression in the formation of rotating hyaline blebs. Aggregates of cells from arrested hybrid embryos are also relatively immobile in culture. The morphogenetic significance of circus movements in normal embryos and gastrula-arrest hybrid embryos is discussed.

Animals↗
PubMed1980

Acquired peripheral arteriovenous fistula in a dog.

A pulsating mass with a continuous bruit was discovered in a dog's flank during routine examination. Based on a history of trauma and clinical signs, an acquired arteriovenous (AV) fistula and a false aneurysm were included in the differential diagnosis. Arteriography confirmed the presence of an AV fistula and outlined the lesion for successful surgical extirpation. Hsitopathologic characteristics of the AV fistula were similar to those in man.

Angiography↗
PubMed1978

Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos. IV. Biochemical and autoradiographic observations on fucose-, glucose-, and mannose-labelled materials.

Normal Rana pipiens gastrulae show more incorporation of isotopically labelled fucose, glucose, and mannose into TCA-insoluble materials than blastulae. Interspecific hybrid embryos which undergo developmental arrest at the onset of gastrulation often synthesize reduced amounts of fucose-, glucose- and mannose-labelled materials. These materials are high-molecular weight and are degraded by Pronase into fragments which are included in Sepharose CL-4B but excluded from Sephadex G-50. Labelled materials contain label predominantly in fucose and galactose with little label in glucose or mannose. Labelled materials migrate slowly on cellulose acetate, bind to DEAE-cellulose and elute at low ionic strength and are precipitated by cetyl pyridinium chloride (CPC) without the addition of carrier compounds. Pulse-chase labelling experiments and light- and electron-microscopic autoradiography were used to examine the site of synthesis, mode of transport, and sites of deposition of fucose-, glucose- and mannose-labelled materials in different developmental stages of normal developing Rana pipiens embryos and interspecific hybrid embryos formed by fertilizing the eggs of R. pipiens with the sperm of R. catesbeiana. In both normal and hybrid embryos, after a 15-30-min pulse, grains are closely associated with juxtanuclear and cytoplasmic collections of membrane-bound vesicles which resemble the Golgi apparatus. In normal embryos following a 15-30-min pulse and a 60-min chase, grains are largely cleared from the cytoplasmic vesicles and deposited in the extracellular spaces or along cell surfaces. In contrast, arrested hybrid embryos given a 15-30-min pulse and a 60-min chase show a marked accumulation of grains over cytoplasmic structures such as the Golgi apparatus and vesicular elements in the cell cortex. Certain interesting features of regional variation in synthetic activity in developing normal embryos are also described.

Animals↗
PubMed1977

Changes in the cell coat at the onset of gastrulation in Xenopus laevis embryos.

Four developmental stages of Xenopus laevis embryos were fixed in standard electron microscopic fixatives with 1% lanthanum nitrate added. This treatment reveals a lanthanum staining material (LSM) on the cell surface and in extracellular spaces. Morula and blastula stage cells have a small amount of LSM; in blastulae, 3 +/- 3 SD % of the cell surface is coated with LSM. In early gastrulae, 29 +/- 6 SD % of the cell periphery is covered with LSM. In late gastrulae, 82 +/- 13 SD % of the cell periphery is either coated with LSM or faces a space with LSM in it. There is also an appreciable accumulation of LSM within extracellular spaces during gastrulation.

Animals↗
PubMed1977

Lectin binding to dissociated cells from two species of Xenopus embryos.

1. Fluorescein isothiocyanate-conjugated concanavalin A (F-conA) and soy bean agglutinin (F-SBA) bind to the surface of EDTA-dissociated cells from blastula and gastrula stage Xenopus laevis and X. mulleri embryos. 2. Binding of these lectins is abolished by appropriate haptens (alpha-methyl-D-mannopyranoside for F-conA and 2-acetamido-2-deoxy-D-galactose for F-sba). 3. Gastrula stage cells show a clustering or capping of lectin binding sites not shown by blastula stage cells. 4. At least for F-conA, this capping is induced by the lectin. 5. There are no striking regional differences in either amount or pattern of lectin binding in early gastrulae of both species.

Animals↗
PubMed1977

Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos. I. Toluidine blue and lanthanum staining.

Four developmental stages of Rana pipiens, R. pipiens female X R. catesbeiana female, and R. pipiens female X R. esculenta male embryos were fixed in standard electron microscopic fixatives with or without 1% lanthanum nitrate (LN) added. Embryos fixed without LN were embedded and sectioned at 0-5 micrometer and stained with toluidine blue. Embryos fixed with LN were embedded and sectioned at 70-80 nm and examined in the electron microscope. Both techiques show a dramatic increase in the amount of stainable material in the extracellular matrix during development. Blastula stage embryos have a small amount of material in the extracellular matrix. Early gastrulae have more stainable material than blastulae and this increased amount appears to be due to an accumulation of material in the marginal zone of the embryo, especially near the dorsal lip of the blastopore. Late gastrulae have large amounts of stainable material in the extracellular spaces in almost all parts of the embryo. Interspecific arrested hybrid embryos do not show the same dramatic accumulation of stainable material in their extracellular matrices.

Animals↗