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D Brown

Publications and source records attributed to D Brown.

At least 775 records · Page 43Linked to original sources
PubMed1989

Functional water channels are present in clathrin-coated vesicles from bovine kidney but not from brain.

Targeting of water channels in renal epithelia may involve trafficking of clathrin-coated vesicles. We have isolated and measured the osmotic water permeability (Pf) of purified clathrin-coated vesicles from bovine kidney cortex and inner medulla, and bovine brain, a tissue not expected to contain "water channels." Brain-coated vesicles had a diameter of 80 nm in negatively stained preparations. Pf was measured by a stopped-flow light scattering technique. In brain-coated vesicles, water transport was functionally homogeneous with a low Pf of 0.0016 +/- 0.0001 cm/s (seven preparations, 23 degrees C). Pf was independent of osmotic gradient size (25-300 mOsm), not inhibited by mercurials, and not altered by removal of the clathrin coat. The activation energy (Ea) for Pf was high (11 +/- 1 kcal/mol less than 34 degrees C, 17 +/- 2 kcal/mol greater than 34 degrees C). Therefore, water channels are absent from brain-coated vesicles. In contrast, there were two functional populations of vesicles in coated vesicle preparations from both kidney cortex and medulla. One population of vesicles had low water permeability and no water channels, whereas a second population had high Pf (0.02 cm/s, 21 degrees C) that was inhibited by HgCl2, and low Ea (2-3 kcal/mol). The fraction of vesicles with high Pf was 52 +/- 3% (S.D., n = 3, cortical vesicles) and 26 +/- 3% (medullary vesicles). These results provide evidence that functional water channels are not present in clathrin-coated vesicles from the brain, whereas they are found in a population of coated vesicles from kidney cortex and medulla, tissues in which water channels are recycled between the plasma membrane, and an intracellular compartment.

Animals↗
PubMed1989

UK-69,578, a novel inhibitor of EC 3.4.24.11 which increases endogenous ANF levels and is natriuretic and diuretic.

A search for potent inhibitors of EC 3.4.24.11, an enzyme which is found most abundantly in the kidney and which degrades atrial natriuretic factor, has led to the identification of UK-69,578. Structure-activity studies starting from substituted N-carboxymethyl dipeptide inhibitors resulted in the introduction of a cyclo-alkane P1' residue and in the replacement of the aza-link between P1 and P1' residues by a methylene group, with a net ten-fold potency gain. UK-69,578 increases endogenous ANF levels and produces natriuretic and diuretic responses intravenously in mice.

Animals↗
PubMed1989

Synergistic activation of granulocyte-macrophage colony-stimulating factor production by IL-1 and IL-2 in murine Th1 cells.

Recent reports indicate that murine CD4+ Th1-type cloned T cells are insensitive to IL-1 because specific IL-1R are not detected on these cells and IL-1 does not modulate proliferative responses. However, we have determined that Th1 clones can respond to IL-1, because they function synergistically with IL-2 to induce granulocyte-macrophage-CSF secretion. This response to IL-1 plus IL-2 could be induced by IL-1 alpha or IL-1 beta and by membrane-bound IL-1 on macrophages. However, IL-1R could not be detected, and Th1 cells did not respond to IL-4 in the presence or absence of IL-1, as measured by either proliferation or granulocyte-macrophage-CSF production. Therefore, IL-1 functioned as a cofactor in Th1 cells stimulated with IL-2, but not with IL-4. A possible mechanism whereby IL-1 activates Th1 cells is discussed.

Animals↗
PubMed1989

Dual effects of G-protein activation on Ca-dependent exocytosis in bovine lactotrophs.

The whole-cell patch-clamp technique was used to measure cell membrane capacitance (Cm) to monitor exocytosis in single-cultured bovine prolactin-secreting cells (lactotrophs) of the anterior pituitary. The cells were dialyzed with solutions containing different concentrations of ionised Ca and non-hydrolyzable GTP analogues (GTP-gamma-S and GMP-PNP) to activate G-proteins. We have identified two distinct effects of G-protein activation on Ca-induced exocytosis: (i) the maximum Cm increase due to intracellular Ca-dependent exocytosis was diminished, suggesting an inhibitory role of G-proteins close to the site of granule fusion, while (ii) the rate of Cm increase (delta Cm/delta t) was facilitated, revealing conversely a stimulatory role of G-proteins in the translocation of secretory granules to the fusion sites.

Animals↗
PubMed1989

Altered gelatinolytic activity by keratoconus corneal cells.

Keratoconus involves thinning and central protuberance of the cornea, scarring and significantly decreased vision. It is one of the major causes of corneal transplantation in this country, but the etiology of this disorder is unclear. In the present study stromal keratocytes were isolated and cultured from normal and keratoconus human corneas. Consistent with the phenotype of cornea thinning, we observed an increased gelatinolytic activity in keratoconus cultures. Characterization of enzyme properties in these cells suggested that gelatinase (type IV collagenase) was responsible for the majority of proteolytic activity found in this system. This elevated gelatinolytic activity was present in spite of lower amounts of total protein being produced by the keratoconus cultures.

Cells, Cultured↗
PubMed1989

Characterization of surface polypeptides on different life-cycle stages of Theileria annulata.

We describe the characterisation of polypeptides located on the surface of Theileria annulata sporozoites, macroschizonts, piroplasms and infected lymphoblastoid cells using surface iodination techniques. The sporozoite stage exhibited a complex profile of surface polypeptides. However, using data from experiments with defined monoclonal antibodies, the sporozoite surface appeared to be composed of several distinct groups of related polypeptides. Analysis of the macroschizont detected seven surface polypeptides, while eight polypeptides were identified for the piroplasm stage. On the basis of molecular weight comparisons, one of the surface polypeptides appeared to be common to the sporozoite, macroschizont and piroplasm. Stage cross-reactive monoclonals failed to immunoprecipitate a surface-radiolabelled polypeptide, and this prohibited the characterisation of a stage common surface antigen. From the surface labelling studies of Theileria-infected and uninfected lymphoblastoid cell lines, we concluded that infection results in major changes at the surface of the host cell, including both the appearance and loss of specific polypeptides. By employing monoclonal antibodies which detect infection-associated determinants, and a polyclonal antiserum raised against a glycoprotein fraction of an infected cell lysate, surface-labelled polypeptides were specifically immunoprecipitated from extracts of infected cells. The polypeptide detected by monoclonal antibody 4H5 was characterised as an infection-associated glycoprotein which varies in molecular mass when immunoprecipitated from different infected cell lines. The identification of infection-associated glycoproteins on the surface of the lymphoblastoid cell suggests that these molecules may be recognised by the cytotoxic T cells of immune animals.

Animals↗
PubMed1989

The effects of fluoride on bone and implant histomorphometry in growing rats.

The effects of fluoride at concentrations of 2.0 and 4.5 mM in drinking water on growth rate, vitamin D, water and mineral metabolism, bone histomorphometry, and osteoinduction of demineralized allogenic bone matrix (DABM) were compared in the rat. Whereas fluoride did not influence fluid intake or growth rate at the lower concentration, it increased fluid intake and inhibited growth rate at the higher concentration. Fluoride produced dose-related increases in serum fluoride and alkaline phosphatase but did not alter serum 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D. Serum calcium and phosphate were reduced by fluoride at concentrations of 2.0 mM but not 4.5 mM. Cancellous bone fractional area was increased by fluoride at 2.0 mM and was reduced by fluoride at 4.5 mM. Fluoride had no effect on cancellous bone surface length or the percentage surface lined by osteoblasts and osteoclasts. Fluoride increased medullary area and decreased the endosteal bone formation rate. Fluoride increased periosteal bone formation and apposition rates at concentrations of 2.0 mM but not 4.5 mM. Fluoride inhibited mineralization in DABM implants, and at the higher concentration, fluoride increased the formation of new bone matrix. These results indicate that in the rat, fluoride increases cortical and trabecular bone at therapeutic doses and reduces trabecular bone at toxic doses. The serum concentration of fluoride at therapeutic doses in the rat is similar to that in patients with osteoporosis who are on treatment with fluoride. In the rat, there is a narrow range between toxic and therapeutic doses.

Alkaline Phosphatase↗