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Biomedical subjects

R Fuchs

Publications and source records attributed to R Fuchs.

At least 145 records · Page 8Linked to original sources
PubMed1986

Electrical and molecular coupling between sodium and proton fluxes in basolateral membrane vesicles of rat liver.

Mechanisms of Na+-H+ exchange in the hepatocyte were studied utilizing isolated basolateral membrane vesicles prepared by two different methods: Evidence was obtained for the existence of molecular coupling of Na+ and H+ fluxes (Na+/H+-antiport) which exhibits saturation kinetics (Km 7 mmol/l Na+) and is inhibited by amiloride (1.0 mmol/l). Although the two membrane preparations showed differences with respect to ionic permeabilities, our data suggest that a relatively high H+ conductance exists in the basolateral plasma membrane. Hence, electrical coupling of conductive H+ and Na+ fluxes in the opposite direction could contribute to net Na+-H+ exchange across the basolateral hepatocyte plasma membrane.

Animals↗
PubMed1986

[Eating and ruminating behavior of sheep. 2. Experiments in pregnant and lactating ewes fed with a straw-concentrate mixture].

Fertility oriented ewes in the late stage of gestation and during the lactation period received 19 feeding regimes on the basis of straw-concentrate mixtures, which essentially differed in the feedstuff structure. The ewes fed ad libitum on average used between 5 and 6 hours per day feed intake in the 86 measuring periods. The average daily ruminating time ranged from 398 to 502 minutes. An increasing straw content resulted in significantly longer ruminating periods and a higher number of masticatory movements, additional quotas of long straw had non effect. But even the most unfavourable feeding variants (straw-concentrate mixtures with 40% straw meal treated with NaOH) elicited 21 100 ruminating masticatory movements in 5 hours of ruminating. There were no significant differences between the absolute consumption and ruminating activities in the late stage of gestation and the lactation period; with reference to feed and crude fibre intake the ruminating expenditure in the late stage of gestation was always significantly higher. Rations with a low structural effect resulted in a more unbalanced distribution of consumption and ruminating activities in the course of the day than well structured rations.

Animals↗
PubMed1986

Chinese hamster ovary cell mutants with temperature-sensitive defects in endocytosis. I. Loss of function on shifting to the nonpermissive temperature.

We have isolated three independent Chinese hamster ovary cell mutants (B3853, I223, and M311) with temperature-sensitive, pleiotropic defects in receptor-mediated endocytosis. Activities affected at 41 degrees C include uptake via the D-mannose 6-phosphate receptor, accumulation of Fe from diferric transferrin, uptake of alpha 2-macroglobulin, compartmentalization of newly synthesized acid hydrolases, resistance to ricin, and sensitivity to diphtheria and Pseudomonas toxins and modeccin. The three mutants also displayed decreased sialylation of some secreted glycoproteins at 41 degrees C, reminiscent of the nonconditional mutant DTG1-5-4 that showed both endocytic and Golgi-associated defects (Robbins, A.R., C. Oliver, J.L. Bateman, S.S. Krag, C.J. Galloway, and I. Mellman, 1984, J. Cell Biol., 99:1296-1308). Phenotypic changes were detectable within 30 min after transfer of the mutants to 41 degrees C; maximal alteration of most susceptible functions was obtained 4 h after temperature shift. At 39 degrees C, the mutants exhibited many but not all of the changes manifested at 41 degrees C; resistance to diphtheria and Pseudomonas toxins required the higher temperature. Analysis of cell hybrids showed that B3853 and DTG1-5-4 are in one complementation group ("End1"); M311 and I223 are in another ("End2"). In the End1 mutants, loss of endocytosis correlated with complete loss of ATP-dependent endosomal acidification in vitro; in the End 2 mutants partial loss of acidification was observed. At the nonpermissive temperature, residual levels of endocytic activity in B3853 and M311 were nearly identical; thus, we conclude that the differences measured in endosomal acidification in vitro reflect the different genetic loci affected, rather than the relative severity of the genetic lesions. The mutations in M311 and I223 appear to have different effects on the same protein; in I223 (but not in M311) the full spectrum of phenotypic changes could be produced at the permissive temperature by inhibition of protein synthesis.

Animals↗
PubMed1986

Distribution of 14C-ochratoxin A in the rainbow trout (Salmo gairdneri).

The nephrotoxic mycotoxin ochratoxin A was studied in rainbow trout by whole-body autoradiography and scintillation counting using 14C-labelled toxin. After one single intravenous injection of 10 muCi/fish, corresponding to 160 ng toxin/g body weight, the tissue affinity was studied during an eight day period. As soon as 5 min. after injection the concentration of the radioactivity in the blood had dropped to one tenth of that in the kidney and the urinary bladder. The autoradiograms showed two patterns of blackening in the kidney, one diffuse in the pronephros and one very strong spotty blackening in the opistonephros. In addition to the kidney very high concentrations of radioactivity were also noticed in the bile and the pseudobranch. The muscular tissue of treated trouts contained almost no radioactivity during the whole experiment. Chemical analysis revealed that the radioactivity that could be extracted from the organs was mainly ochratoxin A.

Animals↗
PubMed1985

Effects of 1 alpha,25-dihydroxycholecalciferol on sodium-ion translocation across chick intestinal brush-border membrane.

By utilizing isolated brush-border vesicles, Na+ transport across the luminal membrane of chick small intestine was found to be a composite of (i) a saturable (Km 10mM-Na+) amiloride-sensitive Na+/H+ antiport and (ii) a potential-sensitive conductive pathway. No evidence was obtained for the existence of a Na+/Cl- symport system. With the exception of the duodenum, luminal Na+ transfer in the entire small intestine was subject to regulation by vitamin D. Repletion of vitamin D-deficient chicks with 1 alpha,25-dihydroxycholecalciferol [1 alpha,25(OH)2D3] significantly decreased net Na+ uptake by isolated membrane vesicles (by approximately 30%). The sterol suppresses the conductive pathway (25-45% inhibition) as well as the Na+/H+ antiport system. Kinetic analysis of the latter revealed that 1 alpha,25(OH)2D3 altered Vmax (from 12.9 to 4.8 nmol of Na+/20s per mg of protein), but did not change Km. Diminution of Na+ transfer, entailing an increase in the electrochemical transmembrane Na+ gradient, provides an explanation of the simultaneously observed stimulatory action of 1 alpha,25(OH)2D3 on Na+-gradient-driven solute transport in chick small intestine. Indirect evidence was obtained that the luminal plasma membrane of chick small intestine displays a definite H+ permeability that is positively affected by 1 alpha,25(OH)2D3.

Amiloride↗
PubMed1985

Levamisole circumvents inhibition of lymphocyte activation imposed by uremic serum.

Uremic serum inhibits thymidine incorporation of phytohemagglutinin-stimulated lymphocytes originating in normal individuals. In this study the effect of levamisole on such inhibition was investigated. Preincubation with a wide range of levamisole concentrations resulted in complete prevention of the inhibitory effect imposed by uremic serum on thymidine incorporation. We would like to suggest that uremic serum possibly inhibits thymidine incorporation of normal lymphocytes by imposing an abnormal cyclic GMP/cyclic AMP intracellular ratio, and that levamisole may restore this ratio to normal.

Adolescent↗
PubMed1984

Screening for ochratoxin A in blood by flow injection analysis.

A micromethod for ochratoxin A detection in human sera by flow injection technique is described. The method requires 50 microliter of sera, and it is designed to distinguish samples containing less than 10 ng ochratoxin A per ml. The method is based on fluorescence measurement following a simple extraction procedure for which very small amounts of chemicals are needed. Since the method is not confirmatory, all samples showing fluorescence above a certain intensity have to be reanalysed with some other method where a confirmation step in included. Because of the small amount of serum needed and the rapid procedure (less than 15 min), a large number of samples can be analysed very quickly. The method may therefore be applicable for large screening campaigns conducted to determine the presence of ochratoxin A in blood. This conclusion is based on 1675 samples and 147 standards analysed concurrently by the flow injection technique and an earlier published enzymic method. The method is also suitable for monitoring ochratoxin A levels in the blood of experimental animals.

Chromatography, High Pressure Liquid↗
PubMed1984

Conversion of ochratoxin C into ochratoxin A in vivo.

The conversion of ochratoxin C to ochratoxin A was studied in rats after oral and intravenous administration. The concentration of ochratoxin A in the blood as a function of time was the same after oral administration of equivalent amounts of either ochratoxin C or ochratoxin A. The maximum ochratoxin A concentrations were measured 60 min after administration. Given intravenously, ochratoxin C was also converted to ochratoxin A. Maximum concentrations were reached after 90 min. It is concluded that ochratoxin C is readily converted to ochratoxin A after both oral and intravenous administration. There is reason to believe that a comparable toxicity of the two toxins is based upon this conversion and that only interference with the biotransformation mechanisms may cause a difference in their toxicity.

Administration, Oral↗