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Biomedical subjects

A Stevens

Publications and source records attributed to A Stevens.

At least 253 records · Page 14Linked to original sources
PubMed1983

Ouabain binding in rectal gland of Squalus acanthias.

In an attempt to examine the mechanisms of activation of (Na, K)-ATPase when epithelial transport is stimulated, the binding of ouabain to rectal gland tissue was measured before and after stimulation with dibutyryl cAMP and theophylline. Stimulation significantly altered the characteristics of ouabain binding to slices of Squalus acanthias rectal gland and to isolated rectal gland cells, accelerating the rate of binding and increasing the amount of ouabain bound at equilibrium when low concentrations of ouabain (10(-9) to 10(-7) M) were present in the medium. Scatchard plots of ouabain binding were nonlinear, suggesting at least two classes of binding sites, one of higher and one of lower affinity. Stimulation with cAMP and theophylline appeared to increase the affinity of the high-affinity site. Ouabain binding was increased by cAMP and theophylline even in the presence of furosemide (10(-4) M) or bumetanide (10(-5) M), and when Li+ was substituted for Na+, or NO3- for Cl- -maneuvers known to inhibit rectal gland secretion. The changes in ouabain binding induced by cAMP and theophylline do not appear, therefore, to be secondary to secretory activity but may reflect a change in the configuration, environment or location of existing enzyme so as to enhance its activity. Stimulation of ouabain binding cannot be demonstrated in whole homogenates of rectal gland, indicating that intact cells are necessary for the cyclic AMP-induced increase in ouabain binding to become manifest.

Animals↗
PubMed1983

Type III glycogenosis presenting as liver disease in adults with atypical histological features.

Two cases of type III glycogen storage disease are reported in adults; the occurrence of cirrhosis in one case illustrates the potential development of chronic liver disease in this condition. The other was the oldest patient with this condition found in a review of published reports. Electron microscopy of peripheral blood leucocytes to demonstrate excess glycogen was found to be a quick and useful aid to diagnosis. Histology of these adult cases showed a distribution of hepatocyte vacuolation which has not been previously recorded.

Adult↗
PubMed1983

Salbutamol and treadmill performance in non-atopic athletes.

Salbutamol and treadmill performance in non-atopic athletes. Med. Sci. Sports Exerc., Vol. 15, No. 6, pp. 520-522, 1983. Nineteen aerobic, non-atopic, athletes (10 females, 9 males) were studied in a double-blind fashion to determine the effect of a therapeutic dosage of salbutamol on pulmonary function, oxygen consumption (VO2max), heart rate (HR), and anaerobic threshold (AT). A placebo and salbutamol (in aerosol form) were administered in a dosage of two puffs four times per day. Forced vital capacity (FVC), FEV1.0, and mid-maximal expiratory flow were assessed prior to a maximal treadmill run, and at 5, 10, and 15 min of recovery. Resting and maximal HR, VO2max, AT, and VE were determined prior to and immediately after the 1-wk experimental period. Pre-test results showed no evidence of airway obstruction in any athlete. There was no significant change in any pulmonary function variable as a result of salbutamol administration. Maximal oxygen consumption showed a slight, nonsignificant (P greater than 0.05) decrease in both the salbutamol and placebo groups. There was also a similar nonsignificant decrease in pulmonary function in both groups. Resting and maximal HR and AT were unchanged. These results indicate that therapeutic administration of a selective beta-2 agonist does not affect pulmonary function or performance-related variables in non-atopic elite athletes.

Adult↗
PubMed1982

HLA antigen expression on urothelial cells: detection by antibody-dependent cell-mediated cytotoxicity.

Antibody-dependent cell-mediated cytotoxicity (ADCC) was used to detect HLA-A, -B and -C antigens on in vitro-cultured urothelial cells of normal or malignant derivation. Alloantisera induced specific lysis of 51Cr-labelled targets by effector lymphoid cells from non-immune donors. HLA antisera were routinely titred to dilutions greater than or equal to 10(-3) on urothelial cells in primary or long-term culture. The HLA phenotype was compared for lymphoid cells and urothelial cells from eight individuals. HLA antigens detected by complement mediated lymphocytotoxicity were also detected on urothelial cells. No deletions or gains in HLA antigens were found on normal or malignant urothelial cultures as compared with donor lymphocyte HLA typings. The results show that the established urothelial cells lines J82, TCCSuP and SCaBER have retained their donor HLA phenotype. The established cell lines T24 and RT4 derived from transitional cell carcinomas and HCV-29 from urothelium were found to have distinctive HLA profiles although donor lymphocytes were not available for comparison. The serological crossreactions seen in complement mediated lymphocytotoxicity were clearly observed in ADCC. In particular, HLA-Cw5 was found to crossreact with HLA-Cw8. HLA-Cw5 was detected on 6/8 cultures of transitional cell carcinomas and this was confirmed by absorption analysis.

Antibody-Dependent Cell Cytotoxicity↗
PubMed1982

Intracellular accumulation of a fluorescent derivative of paromomycin in human fibroblasts.

Human fetal lung fibroblasts grown in the presence of dansyl-paromomycin (DNS-Pm), a fluorescent derivative of the aminoglycoside antibiotic, paromomycin, probably accumulate DNS-Pm in the lysosomes. The intracellular concentration of DNS-Pm is proportional to the extracellular concentration and to the length of time cells are exposed to the compound. The accumulation of DNS-Pm by human fibroblasts continued to increase for several days, reaching a saturation after 7 days. The kinetic data are consistent with the establishment of a steady state in the cell between fluid-phase pinocytosis and exocytosis of DNS-Pm. About 80% of the intracellular DNS-Pm ws released in 24 hr when fresh medium without the analogue was added. The residual 20% remained within the cells, suggesting that it may be irreversibly bound to the lysosomes, endoplasmic reticulum, or ribosomes. The uptake of paromomycin by cells in culture may be a useful means to study error propagation during growth and lifespan of cells in vitro.

Chemical Phenomena↗
PubMed1982

Tapetoretinal degeneration in the cerebro-hepato-renal (Zellweger's) syndrome.

Electrophysiological and histopathological study of a baby suffering from Zellweger's syndrome and presenting progressive retinal dysfunction showed this to be related to degenerative changes in the photoreceptor cells and pigment epithelium and to defective myelination of the optic nerve. Disturbances of bile acid and lysine metabolism were also demonstrated, lending support to the concept that Zellweger's syndrome is attributable to a widespread inadequacy of intracellular oxidative function.

Brain Diseases↗
PubMed1980

Purification and characterization of a Saccharomyces cerevisiae exoribonuclease which yields 5'-mononucleotides by a 5' leads to 3' mode of hydrolysis.

An exoribonuclease producing 5'-mononucleotides has been purified from ribosomes of Saccharomyces cerevisiae. The enzyme has a broad pH optimum around 8.0, requires divalent cation, and is stimulated by monovalent cation with the cation and degree of stimulation being dependent on the substrate used. With either poly(A) or rRNA as substrate, the enzyme has a processive mode of hydrolysis. The oligonucleotides, (pA)3-5, are hydrolyzed by the enzyme, and the hydrolysis is dependent on a 5'-phosphate end group. Phosphorylation of the 3' end has little effect on the rate of hydrolysis. With [3H]poly(A) or [3H]rRNA, labeled differentially at the 5' termini, a more rapid release of 5'-terminal label can be shown, providing evidence that the enzyme hydrolyzes in a 5' leads to 3' direction. Further evidence for a 5' leads to 3' mode of hydrolysis is provided by a study of the products of the hydrolysis of [3H](pA)5 labeled at the 5' termini with 32P. No 32P label is found in (pA)2 which accumulates as an intermediate.

Cations, Divalent↗
PubMed1980

Accuracy of in vitro protein synthesis: translation of polyuridylic acid by cell-free extracts of human fibroblasts.

Errors in translation have been measured in cell-free protein synthesising extracts derived from cultured MRC-5 human diploid fibroblasts of limited lifespan. Using polyuridylic acid as messenger, the error frequency for the misincorporation of leucine was 1-2%. It was found that varying the concentration of leucine increased the error frequency for leucine misincorporation. No difference could be detected in the accuracy of translation with increasing cell age, from passage 25 to 55. The aminoglycoside antibiotic, paromomycin, was shown to have a profound effect on the leucine misincorporation, increasing the error frequency of this amino acid twenty-to fortyfold. However, there was no difference in the paromomycin-induced errors wtih increasing cell age. Another effect of this antibiotic is that it inhibits the incorporation of the cognate amino acid phenylalanine. It was found that passage 55 cell extracts were less inhibited by paromomycin than similar extracts made from lower passage cells (passages 25 and 40). When the accuracy of translation of cell extracts made from human transformed cells (HeLa) and untransformed cells (MRC-5) was compared, no detectable difference could be found. Paromomycin increased the leucine errors in extracts made from HeLa cells to a similar degree to that observed for MRC-5 fibroblasts.

Cell Survival↗