Search PubMed⌕ Search

Biomedical subjects

R Lorenc

Publications and source records attributed to R Lorenc.

At least 55 records · Page 3Linked to original sources
PubMed1985

Activation of liver cytosol phosphoenolpyruvate carboxykinase by Ca2+ through intracellular redistribution of Mn2+.

Calcium has no known direct effect on phosphoenolpyruvate carboxykinase from rat liver cytosol. However, addition of calcium salts to liver postnuclear supernatant led to an increase in assayable enzyme activity in cytosols. This indicates that mitochondria and microsomes present in postnuclear supernatant can participate in observed enzyme activation. The stimulation of phosphoenolpyruvate carboxykinase was prevented by the manganese complexion 1-(2-pyridylazo)-2-naphthol, was not additive with activation by MnCl2 and was inhibited by La3+, Sr2+ and ruthenium red. These data indicate that manganese and mitochondrial or microsomal calcium carriers participate in the mechanism of indirect calcium effect. Measuring of manganese content in cytosols directly, by atomic absorption spectrometry, has provided evidence that there is a pool of manganese associated with mitochondrial and microsomal fraction of rat liver that can be mobilized to the cytosol by calcium ions. The direct addition of this pool of manganese to the cytosol caused the stimulation of phosphoenolpyruvate carboxykinase activity to the same levels as did calcium ions in the postnuclear supernatant. It is postulated that calcium can effect enzyme activity indirectly by releasing manganese from specific cellular compartments into the cytosol.

Animals↗
PubMed1985

Effect of lactose on phosphate transport into rat intestinal brush border membrane vesicles.

Brush border membrane vesicles (BBMV) were used to evaluate the influence of lactose on phosphate (Pi) transport in the intestine of the rat. BBMV were prepared from duodenum, jejunum and ileum of 3-, 4- and 7-wk-old rats. Na+-dependent active transport of Pi was investigated in the presence of an Na+ gradient; Na+-independent, diffusional transport was investigated by substitution of choline chloride for NaCl. In 3-wk-old rats active Pi transport dominated, whereas in 4-wk-old rats a decrease in active transport and an increase of the diffusional component of total Pi transport were observed. Furthermore, in 7-wk-old rats, Pi was transported by simple diffusion alone. Addition of lactose to the preincubation medium had no effect on Pi transport in duodenal and jejunal BBMV isolated from 3-wk-old rats. In the remaining BBMV preparations, lactose caused a twofold enhancement of diffusional Pi uptake. Glucose and galactose had no effect on diffusional Pi uptake into BBMV. These results indicate that lactose may directly interact with luminal membranes, thus leading to increased diffusional transport. The membranes with a decreased Na+-dependent Pi transport activity are most susceptible to the influence of lactose.

Aging↗
PubMed1984

Effects of phosphate anions and some divalent metal cations on phosphoenolpyruvate carboxykinase. Comparison of liver and kidney enzyme.

The effect of calcium and phosphate anions on rat kidney cytosol phosphoenolpyruvate carboxykinase activity was evaluated using enzyme preparations obtained by two purification procedures. The enzyme activity was not significantly affected by calcium ions at physiological concentration. Phosphate inhibited the enzyme in the presence of Fe2+; the inhibition was overcome by Mn2+. Kidney and liver phosphoenolpyruvate carboxykinases show some qualitative differences in their response to Fe2+ and phosphate.

Animals↗
PubMed1983

Rapid high-performance liquid chromatographic method for the estimation of toxicological levels of 25-hydroxycholecalciferol (25-OH D3) in human serum.

A reversed-phase HPLC method for determination of 25-hydroxycholecalciferol (25-OH D3) in serum samples is described. The method involves extraction of 25-OH D3 with hexane, followed by differential resolubilization in acetonitrile. The sample is then applied directly on the C18 bonded phase column of the liquid chromatograph, and developed in a acetonitrile-water solvent system. In the range 12.5-400 ng, a linear relationship was observed between detector response and the amount of 25-OH D3 placed on the column. Also, a very good correlation was observed between the amounts of 25-OH D3 added to serum samples, and the calculated amounts. The method can be used for screening for toxicological levels of 25-OH D3 in patients treated with high doses of vitamin D3.

Calcifediol↗
PubMed1977

Lack of effect of calcitonin on the regulation of vitamin D metabolism in the rat.

The infusion of calcitonin into intact rats increases the accumulation of 1,25-dihydroxy-[26-27-3H]vitamin D3 from 25-hydroxy-[26,27,-3H]vitamin D3 in blood, but has no effect on thyroparathyroidectomized rats using a variety of protocols. Furthermore, the vitamin D status of the animals did not alter the results. Inasmuch as no effect of calcitonin could be found on the accumulation of other vitamin D metabolites as well as 1,25-dihydroxyvitamin D3, it is concluded that calcitonin apparently plays no direct role in the regulation of vitamin D metabolism and that the previous report of an effect of calcitonin on vitamin D metabolism in vivo is probably the result of a secondary response of the parathyroid gland.

Animals↗