Oxidation of cytochrome b5 reduced by ascorbic acid

The steady-state levels of aerobic and anaerobic reduction of cytochrome b5 by ascorbic acid and the initial rates of cytochrome b5 reduction in the presence of ascorbic acid and of anaerobic cytochrome P-450 reduction in the presence of NADH were used to calculate the rate constants for cytochrome b5 oxidation. The rate constant for cytochrome b5 autooxidation in the membrane is equal to that for isolated cytochrome b5, i. e., 5 X 10(-3) s-1 (37 degrees C). The rate constant for the second cytochrome b5 oxidation reaction in the membrane, i. e., electron transfer to cytochrome P-450, is equal to 140 X 10(-3) s-1 (37 degrees C).     

Partial reversion of the phenotype of a poorly differentiated hepatocellular carcinoma in a three-dimensional culture

In vivo, normal tissues and organs have a three-dimensional structure and function in a three-dimensional environment. The standard two-dimensional cell culture conditions drastically differ from those in vivo. For this reason, three-dimensional cultures based on different variants of the extracellular matrix are more adequate for analyzing normal and tumor cell growth. Culturing a poorly differentiated hepatocellular carcinoma in a collagen gel yielded spheroids whose growth pattern shifted towards the epithelial phenotype. The shift was expressed in changes in the cytoskeleton, enhanced formation of extracellular matrix fibrils between cells, and formation of fibronectin fibrils on the outer surface of spheroids. Analysis of 25 genes reflecting the level of morphological and functional hepatocyte differentiation showed that the expression of the gene encoding the transforming growth factor TGFβ2 was suppressed the most significantly.     

Separation and investigation of the regulatory properties of two forms of cyclic nucleotide phosphodiesterase from rabbit heart--sensitive and insensitive to Ca-dependent regulator protein]

Two forms of cyclic nucleotide phosphodiesterase (ES 3.1.4.17)--PDE-I and PDE-II--sensitive and resistant to Ca-dependent protein regulator, were isolated from the soluble fraction of rabbit heart by chromatography on DEAE-cellulose. Both forms of enzyme are inhibited by 30--50% by Ca2+ (10(-4) M). Addition of Ca-dependent protein regulator activates PDE-I and eliminates Ca2+-induced inhibition of PDE-II. In heart extract Ca2+ increases the phosphodiesterase activity 1.5-fold. The amount of PDE-I makes up to about 10% of total phosphodiesterase activity of the heart; that of PDE-II is about 90%. In the presence of Ca-dependent protein regulator the rate of 3', 5'-AMP hydrolysis by PDE-I is increased 5--15-fold, while that of 3', 5'-GMP hydrolysis only 2.5-fold. Both PDE-I and PDE-II have close Km values for substrates--(3.5--4.0).10(-6) M for 3', 5'-AMP and 14.10(-6) M for 3', 5'-GMP. Inhibition by Ca2+ and effect of Ca-dependent protein regulator manifest themselves in changes in V for cyclic nucleotide hydrolysis and do not alter the Km value for the enzyme.     

Adaptive effects of hypoxic preconditioning in brain neurons

A preventive short-term hypoxia (preconditioning) increases neuronal resistance against subsequent strong hypoxic effects. Literature review and authors' own data on molecular-cellular mechanisms of the hypoxic preconditioning, are presented. Participation of intracellular signal transduction, genome, stress-proteins, and neuromodulating peptides in this process, is discussed. The role of glutamatergic as well as calcium and phosphoinositide regulatory systems and neuromodulating factors as the components of a "volume" signal transmission are analyzed in hypoxic precondition-associated induction of functional tolerance mechanisms against acute harmful effects in neurones of olfactory slices.     

Feldspar Tunneling by Fungi along Natural Productivity Gradients

Recently, it was hypothesized that ectomycorrhizas hyphae are involved in mineral tunneling. We evaluated the role of ectomycorrhizas in mineral weathering and the ecosystem influx of basic cations by correlating mineral tunnel density to ectomycorrhizas density in two forest productivity gradients. The gradients, two gentle slopes in northern Sweden, are the result of groundwater movement and are characterized by reduced productivity upslope due to lower nitrogen availability. As expected, ectomycorrhizas density in the O horizon was higher upslope, where nitrogen availability was lower and where the vegetation was dominated by ectomycorrhizas plant species. We consistently found that tunnel formation in mineral grains was more intense in nutrient-poor sites, indicating a higher contribution of fungi to ecosystem influx of potassium and calcium. ectomycorrhizas density was positively correlated with feldspar tunnel density in the upper 2 cm of the E horizon. This suggests that ectomycorrhizas are involved in mineral tunneling. We discuss the possible involvement of ericoid mycorrhizas and saprotrophic fungi in feldspar tunneling and the role of the weathering status of mineral grains as additional factors controlling mineral funneling.     

Changes in the calcium metabolism of cerebral cortical structures in anoxia in vitro

Changes in membrane-bound calcium (Ca2+(b)) content in the brain cortex membrane structures were studied on subcellular fractions (synaptosomes, microsomes, mitochondria) during in vitro anoxia. The changes in Ca2+ content in hydrophobic domains of intracellular membranes were assessed, using chlorotetracycline fluorescent probe. It has been found that membranes of different neuronal compartments are not equally vulnerable to anoxia. A decrease in Ca2+9(b) content in response to anoxia occurs in synaptosomes and microsomes much sooner than in mitochondria. Therefore, Ca2+ release from intracellular membrane compartments, preceding the massive inward flow of extracellular Ca2+, seems to be one of those mechanisms initiating a complex range of intracellular reactions to disturbed oxygen supply in brain cortex neurons.