Calmodulin-dependent Ca2+-pump ATPase of human smooth muscle sarcolemma

An enzymatically active Ca2+-stimulated ATPase has been isolated from the sarcolemmal sheets of human smooth muscle (myometrium). Ca2+-ATPase activity was quantitated in an assay medium which simulated the characteristic free ionic concentrations of the cytosol. New computer programs for calculating the composition of solutions containing metals (Ca, Mg, Na, K) and ligands (EGTA, ATP), based on the updated stability constants, were used. In detergent-soluble form the enzyme has a high Ca2+-affinity expressed by an apparent Km (Ca2+) of 0.25 +/- 0.04 microM. The maximum specific activity (about 20 nmol of Pi/mg protein/min) was found in the micromolar domain of free-Ca2+ concentrations, the same levels required for normal maximal contractions in smooth muscle. The variation of free-Ca2+ concentration in the assay medium over 4 orders of magnitude (pCa 9 to pCa 5) resulted in a sigmoidal dependence of enzymatic activity, with a Hill coefficient of 1.4, which suggested the regulation of Ca2+-ATPase by allosteric effectors. The presence and the activator role of endogenous calmodulin in smooth muscle sarcolemma was proved by calmodulin-depletion experiments and by using suitable anticalmodulinic concentrations of trifluoperazine. The addition of exogenous calmodulin restored the enzyme activity. Apparently, the concentration of calmodulin in isolated smooth muscle sarcolemma is about 0.1% of sarcolemmal proteins, as deduced from the comparison of calmodulin-depletion and calmodulin-readdition experiments. Calmodulin increased significantly the enzyme Ca2+-affinity and Vmax (by a factor of about 10). At variance with the sarcoplasmic reticulum Ca2+-ATPase, the sarcolemmal Ca2+-ATPase is extremely sensitive to orthovanadate, half-maximal inhibition being observed at 0.8 microM vanadate. In conclusion, the Ca2+-ATPase isolated from smooth muscle sarcolemma appears very similar to the well-known Ca2+-pump ATPases of erythrocyte membrane, heart sarcolemma or axolemma. We suggest that this high-affinity Ca2+-ATPase represents the calmodulin-regulated Ca2+-extrusion pump of the smooth muscle sarcolemma.     

Restricted growth of attenuated poliovirus strains in cultured cells of a human neuroblastoma.

Cultured cells of a human neuroblastoma, SK-N-MC, were found to be highly resistant to Sabin attenuated poliovirus types 1 and 2 strains; no appreciable cytopathic effect was observed, and the total harvest was generally in the order of 1 PFU per cell or less. On the other hand, related neurovirulent strains of these antigenic types produced a relatively good (2 orders of magnitude higher) yield in a markedly protracted infectious cycle. The limited growth of the attenuated virus in the neuroblastoma cells appeared to be confined to a minor cell subpopulation. Experiments with intratypic (type 1) poliovirus recombinants suggested that the major genetic determinants limiting reproduction of the attenuated polioviruses in the neuroblastoma cells are located in the 5' half of the viral RNA, although the 3' half also appears to contribute somewhat to this phenotype. The possibility that neuroblastoma cells may represent an in vitro model for studying poliovirus neurovirulence is briefly discussed.     

Protective effect of hypothermia on brain neurons in rats exposed to ionizing radiation

The protein-synthesizing system of hippocampal (CA1, CA3) and sensorimotor cortex neurons is damaged less and recovers much quicker in rats exposed to 8 Gy of γ-radiation under hypoxia/hypercapnia (body temperature 16–18°C) than under usual conditions, as evidenced by microfluorimetry and electron microscopy. The radioprotective effect does not cover the membrane structures (endoplasmic reticulum and Golgi complex), and their restoration is not so prompt.     

The content of NCAM in rat brain structures in conditioned passive avoidance reactions

The content of neural cell adhesion molecule, NCAM, was measured in the brain of rats that acquired a habit of passive defensive behavior, and rats that lost or preserved this habit after electroshock. A significant increase in the NCAM concentration in the striatum was observed in amnesiated animals. These results may be evidence of plastic rearrangements of neuronal networks, responsible for learning and memory, and direct involvement of NCAM in these modifications.     

Plant reaction to drilling wastes of petroleum complex in the zone of Middle Taiga of Ob region

Data on the change in plant condition under the impact of drilling wastes (DWs) of petroleum clefts and on the transport of toxic elements from the stratum (soil) to vegetative organs are obtained. Stimulation of plant growth and productivity is revealed at a DW concentration in oligotrophic strata of up to 20% without translocations of their separate elements in vegetative organs.     

Taking into account the conformational dynamics of macromolecules when analyzing luminescent probe signals

A mathematical model is proposed that takes into account the specific features of electronic excitation energy transfer between the molecular probes sorbed on a polymeric chain in a liquid solution. The kinetics of the process is described from the standpoint of the stochastic changes in macromolecular conformations. The results of numerical solution of the problem are described, as well as the analytical expressions obtained in the context of perturbation theory for a low transfer rate and/or fast conformational dynamics of the macrochain. A channel of nonlinear (with respect to excitation) deactivation resulting from binary annihilation of closely spaced excited centers is considered. Expressions for the efficient rate of mutual quenching and delayed annihilation fluorescence of the probe are obtained. The time dependences of characteristic luminescent signals and the parametric curves of relative fluorescence quantum yield are given.