On the mechanism of shrinkage-induced potassium influx in rat and human erythrocytes.

The rates of 86Rb influx into human and rat erythrocytes were studied in media of various tonicity. At sucrose concentrations below 0.3 mol/l, the ouabain-insensitive, furosemide-inhibited component of influx increased in rat but not in human erythrocytes; this may be explained by a rise in the rate of Na+, K+, Cl-- and/or K+, Cl-cotransport. An increase in osmolarity resulted in a reduction of this as well as of the ouabain and furosemide-insensitive component in rat erythrocytes. At the same conditions a drastic inhibition of Na+, K(+)-pump occurred both in rat and human erythrocytes. We failed to observe a lag-phase in the activation of the cotransport in rat erythrocytes; i. e. the process of activation parallels the shrinkage of cells. In rat erythrocyte ghosts, the shrinkage-induced stimulation of the cotransport was lost, and the direction of their osmotic reaction (inhibition of transport pathways) was similar to that in human erythrocyte ghosts. It is suggested that the mechanism of volume regulation of ion transport in intact cells involves a step of physical amplification via a change in interactions between the protein carcass and the lipid bilayer.     

Simulation of the distribution of spinocerebellar ataxia type 1 in Yakut populations: Description of the model

A simulation model has been developed for predicting the distribution of trinucleotide repeat expansion diseases in human populations. The interface of the software used to run this model presents the options for simulating natural reproduction of a population, with the population demographic parameters taken into account, and for simulating the appearance of a dynamic mutation in populations, transmission of the mutant gene from parents to offspring, and the effect of the phenotypic expression of the disease (the patients’ life expectancy and birthrate) on the transmission of the mutant allele in the patients’ families and its accumulation in the population.     

Intercellular interactions as a reason for the influence of the erythrocyte concentration on the parameters of detergent hemolysis

Possible reasons are discussed for the abnormal erythrocyte concentration influence on the course of detergent hemolysis curves. The data obtained lead to a conclusion that erythrocyte plasma membrane properties and, as a consequence, the parameters of erythrocyte-detergent interaction are dependent on cell concentration. The dependence is more sharply expressed for concentrations 5.10(7) cell/ml. In the concentration range (5-20) X 10(7) cell/ml the state of erythrocyte membrane remains apparently unchanged.     

Streptoverticillium griseoviridum n. sp., a producer of the candidin-amphotericin B group, antifungal heptaene nonaromatic antibiotic 0185]

An actinomyceteous strain LIA-0185 producing a heptaenic non-aromatic antibiotic of the candidin type was isolated from a soil sample taken in the Georgian SSR under the programme of screening antifungal antibiotics. The taxonomic study of the strain showed that it belonged to the series of viridoflavum and had the following main taxonomic features: the sporophores in the whorls, straight, remote: the aerial mycelium from yellow to dark-olive-grey; the substrate mycelium olive; the soluble pigment absent; the melanine pigment was produced on the peptone medium; the culture formed H2S; assimilated glucose, mannose, inozide and to a lesser extent fructose; did not assimilate arabinose, xylose, sucrose, lactose, ramnose and raffinose. The strain inhibited the growth of yeast and fungi, grampositive bacteria and actinomycetes and produced a complex of non-aromatic heptaenic antibiotics. The actinomycete differed from the other whorl cultures. It was classified as a new species Sv. griseoviridum sp. nov. The antibiotic complex was a mixture of 2 components, i. e. I and II present approximately in equal amounts. Component II was analogous to candidin. Component I was a new original substance.     

Inactivation of muscarinic acetylcholine receptors in brain synaptic membranes by free fatty acids. Evaluation of the role of lipid phase

Arachidonic, linolenic and linoleic acids decreased the binding of the m-cholinergic antagonist [3H] QNB and did not affect the ratio of high to low affinity binding sites to the agonist carbamoylcholine in rat brain synaptic membranes. In the presence of arachidonic acid, SH-reagent N-ethylmaleimide acquired the ability to block QNB binding to receptor. Lipids in the bilayer and annular regions were probed by fluorescence of 1,6-diphenyl-1, 3, 5-hexatriene and pyrene. A microviscosity drop induced by increasing temperature from 10 to 37 degrees C did not affect the level of QNB equilibrium binding, whereas arachidonic acid strongly inhibited the binding at concentrations inducing the same drop in microviscosity as that induced by heating. For various unsaturated fatty acids an equal extent of receptor blocking was reached at quite different degrees of bilayer fluidization, the state of annular lipid being not changed under these conditions. It is suggested that the effect of unsaturated acids is reached through their direct interaction with the receptor, which undergoes a conformational change, rather than by an alteration of the physical state of the lipid phase of the membrane.     

Cis- and trans-acting influences on telomeric position effect in Drosophila melanogaster detected with a subterminal transgene

One model of telomeric position effect (TPE) in Drosophila melanogaster proposes that reporter genes in the vicinity of telomeres are repressed by subterminal telomere-associated sequences (TAS) and that variegation of these genes is the result of competition between the repressive effects of TAS and the stimulating effects of promoters in the terminal HeT-A transposon array. The data presented here support this model, but also suggest that TPE is more complex. Activity of a telomeric white reporter gene increases in response to deletion of some or all of the TAS on the homolog. Only transgenes next to fairly long HeT-A arrays respond to this trans-interaction. HeT-A arrays of 6-18 kb respond by increasing the number of dark spots on the eye, while longer arrays increase the background eye color or increase the number of spots sufficiently to cause them to merge. Thus, expression of a subtelomeric reporter gene is influenced by the telomere structure in cis and trans. We propose that the forces involved in telomere length regulation in Drosophila are the underlying forces that manifest themselves as TPE. In the wild-type telomere TAS may play an important role in controlling telomere elongation by repressing HeT-A promoter activity. Modulation of this repression by the homolog may thus regulate telomere elongation.