Individual aortic baroreceptors are sensitive to different ranges of blood pressures

Many receptors,including thermal receptors and mechanical receptors,are only activated by stimuli within a clearly defined range of intensities.Differences in the receptive ranges enable individual receptors and their sensory centers to precisely detect the intensity of the stimulus and changes in intensity.Baroreceptors are the sensory terminals of the baroreflex.It is well understood that an increasing number of baroreceptors are recruited to produce afferent action potentials as the blood pressure increases,indicating that individual baroreceptors have different pressure thresholds.The present study revealed that individual baroreceptors could stop their afferent signals when the blood pressure exceeds a certain level,indicating that individual baroreceptors are sensitive to a specific range of blood pressure.The receptive ranges of individual baroreceptors differ in terms of the total range,the lower threshold,and the upper threshold.Of 85 baroreceptors examined in this study,the upper thresholds for about half were within the physiological blood pressure range.These results indicate that supraphysiological blood pressure is unlikely to be encoded by the recruitment of more baroreceptors.Instead,supraphysiological blood pressure levels might be signaled by an increase in the frequency of action potentials or by other mechanisms.In conclusion,our results indicate that rabbit baroreceptors are activated by blood pressure levels within specific receptive ranges.These findings should encourage further studies to examine the role of population coding of blood pressure by baroreceptors in the baroreflex.     

Problems of biochemical organization]

Biological organization has been defined as a unity of structure, function and regulation. Biological organization of hierarchical multilevel biological systems is represented by a hierarchy of functioning controllable structures. The hierarchy of levels of material organization predetermines the existence of a hierarchy of regulatory mechanisms. Biochemical organization involves the levels of material organization corresponding to biomacromolecules, supramolecular complexes and cellular organelles. The levels of biomacromolecules and supramolecular structures effectuating elementary functions and controlled by basic regulatory mechanisms occupy key positions in biological systems. These levels play the role of standard functional blocks; their combination leads to hierarchically higher structural levels (cell, tissue, organ, systems of organs, organism) performing more complex functions and controlled by hierarchically more important regulatory mechanisms. The peculiarities of regulation of biological systems that are due to the existence of a hierarchy of regulatory mechanisms are discussed.     

Principles of prokaryotic genome organization]

The peculiarities of bacterial chromosome organization are discussed, based mainly on the data on Escherichia coli. Highly important for bacterial genome organization is its division into two approx. equal half-genomes undergoing periodically "exchanges" of some kind displayed as continuous inversions including the oriC region of replication initiation. It is believed that short oligonucleotides are comprised in either of half-genomes. The former are predominantly oriented as direct repeats, which ensures the possibility of formation of tandem duplications consisting of identical genes--under conditions when selection for enhancing functions of corresponding genes takes place. Multiple tandem duplications capable of excision of plasmatic gene copies seem to initiate horizontal gene transfer in bacteria. Tandem gene duplications are probably being formed in the process of bacterial genetic recombination as well, when, as a result of non-equal crossing over, gene alleles derived from different strains are united into a tandem.     

Roentgeno-endovascular dilation of aortic coarctation]

The potentialities of roentgeno-endovascular dilation (RED) of various types of coarctation and aortic stenoses were studied in 12 patients aged 9 to 27. RED was performed by two Grüntzig's catheters with balloons not less than 7 mm in diameter. The main criterion of RED efficacy was a gradient of systolic pressure which was on the decrease by 25-40 mm Hg after using one catheter, and by 40-70 mm Hg after using both catheters. The same method was applied to dilation of stenosis of the abdominal aorta. The proposed method is low invasive and most effective in patients with aortic segmentation of segmental type, and makes it possible to avoid in many cases surgical intervention.     

Unloading arterial baroreceptors causes neurogenic hypertension

We developed a new model to examine the role of arterial baroreceptors in the long-term control of mean arterial pressure (MAP) in dogs. Baroreceptors in the aortic arch and one carotid sinus were denervated, and catheters were implanted in the descending aorta and common carotid arteries. MAP and carotid sinus pressure (CSP) averaged 104 +/- 2 and 102 +/- 2 mmHg (means +/- 1 SE), respectively, during a 5-day control period. Baroreceptor unloading was induced by ligation of the common carotid artery proximal to the innervated sinus (n = 6 dogs). MAP and CSP averaged 127 +/- 7 and 100 +/- 3 mmHg, respectively, during the 7-day period of baroreceptor unloading. MAP was significantly elevated (P < 0.01) compared to control, but CSP was unchanged. Heart rate and plasma renin activity increased significantly in response to baroreceptor unloading. Removal of the ligature to restore normal flow through the carotid resulted in normalization of all variables. Ligation of the carotid below a denervated sinus (n = 4) caused a significant decrease in CSP but no systemic hypertension. These results indicate that chronic unloading of carotid baroreceptors can produce neurogenic hypertension and provide strong evidence that arterial baroreceptors are involved in the long-term control of blood pressure.     

Submicroscopic organization of listeriae during L-transformation]

A study was made of the ultrastructural organization of listeria at the early stages of L-transformation, beginning from the first passage of the bacterial culture on solid nutrient medium with pencillin. The use of potassium benzylpenicillin salt in the capacity of an L-transforming agent permitted to observe the cells at various stages of L-transformation, beginning from the bacterial forms and ending with the typical L-colonies. It was shown that at the earliest stage of L-transformation there occurred not only destruction of the cell wall and the discharge of the mesosomes from the cell, but also significant changes in the nuclear apparatus of the cell. As soon as the second passage the freshly isolated L-forms displayed an internal membrane system in the form of myelin-like structures located under the external membrane, and of individual membranes in the cytoplasm not forming mesosomes. A substance of a medium electrone density resembling the material of the cell wall appeared on the cytoplasmic membrane (in some of its regions).     

Principles of spatial organization of cellular sheets]

The principles of the spatial organisation of epithelial sheets are described, and a new approach to studying their histoarchitecture is proposed. The approach is based on the concept of modular structure of tissues and consists in constructing a family of topological and geometrical models of tissue structure and their experimental verification. Theoretical evidence was obtained that at least 11 topological variants of cell mosaic patterns can be realized in simple epithelia but not one as has been suggested so far. Nine variants of epithelial mosaics predicted have been found experimentally in various animals, and the discovery of the other two is expected in the future. New thus far unknown properties of tissues such as translation symmetry and stoichiometry of the composition were described. By using this approach, it is possible to predict and find new variants of topology of multirow and multilayer epithelia and prognose their changes during normal and pathological morphogenesis.     

Ultrastructure of carotid baroreceptors in the goat.

The initial segment of the occipital artery of the goat appears modified under the electron microscope; endothelial cells are low cuboidal, the tunica media contains many elastic lamellae, and there are few smooth muscle cells. Free afferent nerve endings are seen in this modified arterial wall. They closely resemble the presumptive baroreceptor endings reported in other mammals in their mitochondrial content and abnormal organelles and are interpreted as solely adapting baroreceptors. Special topographical relations between the endings and elastic or collagen fibres do not occur, but microfilaments are present in the vicinity of these endings. Presumptive adrenergic efferent endings are not found in the region of the baroreceptors. We suggest that this zone of the occipited artery is homologous to the carotid sinus.     

Spatial organization of cytochrome oxidase subunit II]

We have studied the tryptic digestion and cyanogen bromide cleavage of the tritium-labelled subunit II from bovine cytochrome oxidase. Basing on the radioactivity distribution in the peptides obtained we suggest a model for the spatial structure of the title subunit.     

Supermolecular organization of apolipoprotein E in solution]

The aggregation behaviour and stability in solution of apolipoprotein E (apoE) isolated from human blood plasma very low density lipoproteins were investigated. The equilibrium denaturation of fluorescein-labeled apoE by guanidine-hydrochloride determined by anisotropy and overall intensity of fluorescence, shift of the emission spectrum maximum and gel-chromatographic behaviour was characterized by reversibility, biphasity, apoE concentration dependence and the existence of native structure of the apoE monomer. The contribution of the long-living component to the kinetic dependence of fluorescence anisotropy in the presence of the 6 M denaturant increased with an increase in apoE concentration. The data obtained fit into the following scheme: oligomer (upon aging of the preparation) in equilibrium tetramer in equilibrium native monomer in equilibrium denaturated monomer. The presence in the tetrameric structure of apoE of two domains is postulated; one of those is formed by lipid-binding fragments during aggregation of individual molecules of apoE. Monoclonal antibody 3D12F11 (subclass IgG1) showed a high affinity for the apoE (Kd = 3.5 +/- 0.5 nM) without any effect on the apoprotein binding to heparin-Sepharose and apoE-induced destruction of dipalmitoylphosphatidylcholine liposomes. It is concluded that the 3D12F11 epitope is localized outside heparin- and lipid-binding sites of the apoprotein molecule.