Acta biologica et medica Germanica最新文献

The channel-forming antibiotic gramicidin A increases the K+ conductance of frog skeletal muscle fibres in isotonic K2SO4 solution. The conductance of the gramicidin channel is not affected by Rb+ or Cs+, but is reduced by T1+. In contrast, the conductance of the normal K+ channel is decreased by Rb+ and Cs+ but is nearly unaffected by 5 and 10 mM T1+. The results suggest differences in the cation permeation through the gramicidin and the K+ channel of the muscle cell membrane.

An ouabain-insensitive, Mg++-dependent, Na+-stimulated ATPase activity which is inhibited by furosemide was found in mucosal homogenate of rat small intestine. The subcellular localization of this ATPase activity was studied by means of isolated purified brush borders and basolateral plasma membranes. The results suggest a nearly identical distribution of Na+-activated and (Na+K+)-activated ATPase within the epithelial cells. Under conditions of alloxan and streptozotocin diabetes an increase of both ATPase activities can be found only in the basolateral plasma membranes. These observations agree well with the convective model of intestinal absorption.

The norepinephrine content of neocortex, hippocampus, and adrenals of adult male Wistar rats was estimated. In normal rats an asymmetrical right-left-distribution of the norepinephrine content was found. Neocortex and hippocampus showed a contralateral, neocortex and adrenals an ipsilateral ratio. Chronic stress cancelled this right-left asymmetry of norepinephrine distribution. In brain the levelling appeared earlier than in adrenals.

Using a microelectrode technique the influence of experimental conditions which are known to alter the intracellular free Ca concentration upon the repolarization phase in the rabbit atrial myocardium was studied. Under all the tested conditions (increased external Ca concentration, application of ouabain, decreased external K concentration) a positive inotropic effect was observed. The action potentials showed a rapid initial repolarization. The positive inotropic effect was found to be well correlated with the effect of the action potential's shortening at 25% repolarization. After pacing pauses a positive correlation between the velocity of the initial rapid repolarization and the potentiation of the atrial contraction was established. It is discussed that all the conditions were able to increase the internal Ca concentration and that in consequence of it a CA-sensitive outward current at potentials about 40 mV more positive than the resting potential is activated.

Rye germ lectin was isolated by extraction of defatted rye germ, fractionation of the extract by ammonium sulfate precipitation, affinity chromatography of the active substances on chitin-beta-glucan and gel filtration on Sephadex G-50. The lectin shows erythroagglutinating activity at a minimum concentration of 2.5 micrograms/ml. The erythroagglutinating activity is the same against human red blood cells of all types of the ABO system and is inhibited by N-acetyl-D-glucosamine. The lectin has no mitogenic activity against mouse splenic lymphocytes. According to the results of polyacrylamide gel electrophoresis the lectin obtained is a mixture of three very similar isolectins of equal erythroagglutinating activity. Sedimentation analysis indicates homogeneity of the lectin preparation; the molecular weight was 56000 as estimated by sedimentation equilibrium. In the presence of urea and sodium dodecyl sulfate the lectin dissociates into 2 types of subunits with molecular weights of 35000 and 19000. The rye germ lectin contains about 2% of neutral sugar and 1% of D-glucosamine. The amino acid composition of the lectin is characterized by a very high content of glycine and half cystine and a low content of apolar amino acids. N-terminal amino acids of the lectin are apparently blocked.

The kinetic parameters Km and kcat and the proteolytic coefficients kcat/Km for the hydrolysis of eighteen Z(benzyloxycarbonyl)-dipeptide methyl esters with variation of the residues in P1 and P2 position catalyzed by thermitase at pH 8 and 55 degrees C are reported. The results indicate that an integral part of both subsites, S1 and S2, are hydrophobic areas and that a mutual interaction between the side chains of P1 and P2 for optimal hydrolyisis does exist. Furthermore, the importance of the P2 for the peptidolytic activity of thermitase was shown using N-acylated oligo-alanine peptides and their p-nitroanilides. In all cases dialanine or alanine p-nitroanilide are the main products.

The effect of acetylsalicylic acid (ASA) on tissue sensitivity to insulin was studied in 14 non-obese subjects with impaired glucose tolerance. For the determination of insulin sensitivity a 1 h priming dose-constant insulin infusion technique was used. The percent decrease of plasma glucose and non-esterified fatty acid (NEFA) concentration at comparable steady-state insulin levels was taken as a measure of body sensitivity to insulin. Patients were restudied after daily treatment with 3.0 g ASA over 3 days. The decrease in plasma glucose and NEFA concentration was in the same range prior to and after ASA treatment (20.1 +/- 3.4 vs 20.8 +/- 4.9% and 54.2 +/- 4.8 vs 54.2 +/- 5.4%), indicating no change of insulin sensitivity by ASA treatment. The mean C-peptide concentration during the insulin infusion test did not differ between the two studies. The metabolic clearance rate of insulin was slightly reduced and the disappearance time of insulin was increased after treatment with ASA. In conclusion ASA did not exert any effect on tissue sensitivity to insulin in subjects with impaired glucose tolerance.

The probable role of cell surface antigens in the development of juvenile diabetes necessitates a detailed study of the proteins expressed on the surface of pancreatic beta-cells. A gene library composed of genes expressed in beta-cells was constructed to provide a source of low abundance genes from those cells. Initial studies with this library have led to the isolation of three genes which share nucleotide and amino acid sequence homology with mouse and human class I major histocompatibility antigens.

The fluorescence of ethidium bromide bound to the DNA of bull spermatozoa can be used for the estimation of intactness and concentration of spermatozoa of washed sperm samples. For the full permeability of the spermatozoal membrane for ethidium bromide digitonin is used in a concentration of 50 micrograms/ml. The fluorescence signals before and after digitonin treatment reflect the portion of cells with intact cellular membrane in the sample. The signal after addition of digitonin correlates to a high degree with the sperm concentration. The method exhibits a sufficient accuracy for the estimation of sperm quality. That applies for the reproducibility with individual ejaculates as well as for the correlation to other methods determining the intactness and sperm concentration. This simple single-step technique requires only about 2 X 10(7) spermatozoa corresponding to 10 to 20 microliters of an average bull ejaculate.