Computer simulations of pacemaker shift in the sinoatrial node

The initiation and propagation of electrical pulses in the sinoatrial node under normal conditions and after application of acetylcholine have been simulated. It has been found that normally a single or a few leading centers are formed in the tissue. When acetylcholine is applied, a temporary functional block of conduction may appear; the leading center migrates under these conditions.     

Compartmentalized energy transfer in cardiomyocytes: use of mathematical modeling for analysis of in vivo regulation of respiration.

The mathematical model of the compartmentalized energy transfer system in cardiac myocytes presented includes mitochondrial synthesis of ATP by ATP synthase, phosphocreatine production in the coupled mitochondrial creatine kinase reaction, the myofibrillar and cytoplasmic creatine kinase reactions, ATP utilization by actomyosin ATPase during the contraction cycle, and diffusional exchange of metabolites between different compartments. The model was used to calculate the changes in metabolite profiles during the cardiac cycle, metabolite and energy fluxes in different cellular compartments at high workload (corresponding to the rate of oxygen consumption of 46 mu atoms of O.(g wet mass)-1.min-1) under varying conditions of restricted ADP diffusion across mitochondrial outer membrane and creatine kinase isoenzyme "switchoff." In the complete system, restricted diffusion of ADP across the outer mitochondrial membrane stabilizes phosphocreatine production in cardiac mitochondria and increases the role of the phosphocreatine shuttle in energy transport and respiration regulation. Selective inhibition of myoplasmic or mitochondrial creatine kinase (modeling the experiments with transgenic animals) results in "takeover" of their function by another, active creatine kinase isoenzyme. This mathematical modeling also shows that assumption of the creatine kinase equilibrium in the cell may only be a very rough approximation to the reality at increased workload. The mathematical model developed can be used as a basis for further quantitative analyses of energy fluxes in the cell and their regulation, particularly by adding modules for adenylate kinase, the glycolytic system, and other reactions of energy metabolism of the cell.     

Specificity of the hemodynamic indices’ shift in SHR line rats at different age

Specificities of the changes in the systemic hemodynamics indices in the spontaneously hypertensive line SHR rats have been studied in comparison with the normotensive line WKY rats. It was demonstrated that an increase in blood pressure observed in the young hypertensive male rats, which have completed puberty (8 weeks old), is associated with the development of the hyperkinetic type arterial hypertension, which is characterized by increased cardiac minute output. It has been shown that SHR line male rats reveal the establishment of stable arterial hypertension due to a significant increase in the total peripheral resistance with the simultaneous recovery of the cardiac minute output by the 25th week of life. SHR line rats at the age of 15 weeks may be regarded as being in the period of transition from the hyperkinetic type arterial hypertension to stable arterial hypertension.     

Changes in conditioned reflex activity during adaptation of the rat to pressure-chamber and high-altitude hypoxia

A group of rats with a stereotype of conditioned reflexes was preliminarily trained to hypoxia effects during 30 days (at the "altitude" of 6000 m, time of exhibition--from 10 to 60 min, for 18 days--only 60 min). Adaptive changes in the process of training consisted in a weakening of differentiation inhibition, partial amnesia of the conditioned reaction of active avoidance and appearance of phasic states (equalization and paradoxical phases) in the cerebral cortex. The following adaptation of hypoxia "trained" rats to new natural conditions of Alpine altitude (3200 m) proceeded favourably, without disturbance of differentiation inhibition and without phasic states. Rats without preliminary training to altitude chamber hypoxia, in mountains (3200 m) were subjected to moderate tension resulting in protective inhibition, partial amnesia and transient disturbance of differentiation inhibition.     

Nitroprusside ions as a liposome label

It has been shown that nitroprusside ions incorporated into bilayer liposomes may be used as a label to form an opinion as to the liposome intactness in the blood and distribution in animal organ tissues in vivo.     

Bone tumors and androgen metabolism]

The paper provides data of comparative assessment of activity of the key enzymes in metabolism of androgens in various morphological variants of sarcomas and benign bone tumors in 46 patients within the age range from 15 to 61, which were under treatment in the ORC named after N. N. Blokhin, RAMS, from 1996 to 1997. On the basis on publications and our own research results we can suggest that malignant human bone tumors of various histogenesis are subject to metabolic processes of testosterone (T), the principal androgen regulator in the bone tissue, as well as formation in bones of 5 alpha-dihydrotestosterone (DHT). One cannot exclude a possibility that metabolism of androgen in bone tissues is directed towards formation of other androgens (in addition to DHT), which may participate in the bone tissue regulation, for instance, 3 alpha- and 3 beta-diols; specific activity of the latter has recently been intensively scrutinized. One can expect that further research shall disclose the clinical significance of metabolism of androgens and of individual androgens in human bone formations.     

Parametric Excitation of Surface Electromagnetic Waves by a Pump Wave Incident Obliquely on a Semi-Infinite Plasma

Plasma Physics Reports - Parametric excitation of surface waves by an s-polarized electromagnetic wave incident obliquely on a semi-infinite supercritical plasma is considered. The growth rates and...