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Biomedical subjects

F F Bukauskas

Publications and source records attributed to F F Bukauskas.

54 records · Page 3Linked to original sources
PubMed1979

[Electrophysiological aspects of the interrelationship between the normal and hypoxic portions of the myocardium].

The results of studying the electrophysiological parameters on the boundary between the normal and the hypoxic area of the myocardium are discussed. The experiments were conducted on isolated preparation of the rabbit atrium with the use of microelectrodes for recording the transmembrane action potentials. The existence of the "maintenance" effect is shown, which is manifested by the better survival of the hypoxic area located nearer to the transitional zone as compared to the survival of a more distant area. The "maintenance" effect is due to the electrotonic interrelationship and to the intercellular diffuse processes of the ions and metabolites. With the continuation of the effect of hypoxia, the transitional zone becomes narrower, one of the causes of which is the disturbed intercellular relationship.

Action Potentials↗
PubMed1977

[Automatism of the sino-atrial node and sinoatrial conduction of excitation in hypoxia].

The effect of experimental hypoxia on the automatic activity of the sinus node and sinoauricular transmission of excitation was studied in 17 isolated preparations of rabbit hearts. A greater frequency of the shifts of sinoauricular delay was noted under hypoxia. Local electrophoretic applications of adrenalin demonstrated that the shifts of the delay occur because of the shifts of pacemakers. The mean frequency of the automatic activity recorded in the atria falls to zero between 6 and 20 min of hypoxia. Hypoxia causes the development of sinoauricular blocks and atrial arrhythmias in the form of individual extrasystoles, high-frequency discharges, or alternations of series of impulses with "mute" periods. The increased tendency towards arrhythmias in the sinoauricular zone is, according to the authors, due to the growing heterogeneity of the duration of action potentials that increases more than three-fold by the 10th minute of hypoxia. The possible reflection of the excitation wave ("echo") from the sinus node zone with an inhibited excitability was demonstrated.

Action Potentials↗
PubMed1976

[Effect of hypoxia on intercellular interaction in the myocardium].

Passive electrical properties of rabbit papillary muscle were studied under normal and hypoxic conditions. The input resistance and the lenght of the electrotonic decay were measured. The results obtained suggested that within a frame-work of a two-dimentional model for anisotropic syncytium the resistance of electrogenic membrane displayed a 1.4-fold decrease on the 10th min after the onset of the hypoxic condition: also the longitudinal (sigma x) and the transverse (sigma y) resistances of the intracellular medium of the syncytium increase 1.39- and 1.3-fold, respectively. An increase in the sigma x and sigma y should be ascribed to the increase in the contact membrane resistance. Derangement of the intercellular interaction under hypoxic conditions is of importance for the understanding of the mechanisms operating in the cardiac arrhythmia due to heart ischemia or myocardial infarction.

Animals↗
PubMedDate not supplied

Pore-lining residues identified by single channel SCAM studies in Cx46 hemichannels.

The substituted cysteine accessibility method was applied to single Cx46 hemichannels to identify residues that participate in lining the aqueous pore of channels formed of connexins. Criteria for assignment to the pore included reactivity to sulfydryl-specific methanethiosulfonate (MTS) reagents from both sides of an open hemichannel and observable effects on open channel properties. We demonstrate reactivity to MTS reagents over a stretch of seventeen amino acids, D51 through L35, that constitute segments of E1 and TM1. Qualitatively, the nature of the effects caused by the Cys substitutions alone and their modification with MTS reagents of either charge indicate side chain valence is most influential in determining single channel properties with D51 and L35 defining the extracellular and intracellular limits, respectively, of the identified pore-lining region. A number of Cys substitutions beyond L35 in TM1 caused severe alterations in hemichannel function and precluded assignment to the pore. Although all six subunits can be modified by smaller MTS reagents, modifications appear limited to fewer subunits with larger reagents.

Amino Acid Substitution↗
PubMedDate not supplied

[Dicrete zones of electrical connection between Purkinje terminals and muscle fibers in dog ventricles].

Activity of Purkinje terminals (P) and neighbouring muscle (M) fibres (P -- M-pairs) in various regions of dog's right ventricle was recorded. It has been shown that transmission of stimulation from P-to M-fibres is abserved not over all endocardial surface, rather in descrete sites -- zones of P--M-interaction. The zones ellips like with the axes 300X100 micron, they are located relatively far from one another -- at the distance of 800-2000 microns. The total area of the zones equals 5% of endocardial surface. P-M delay is less within the zone of connection of P--M-fibres (4 msec) and greater outside the zone (up to 10 msec).

Action Potentials↗
PubMedDate not supplied

[Anisotropy of stationary rates and delays in extrasystolic waves in the dog heart].

Excitation propagation in the ventricle and auricle bands of the dog's myocardium has been studied. The anisotropy of stationary valocities and delays of the initiation of extrasistole exciation has been shown: along the fibres the velocity is higher and the delay smaller than across the fibres. The levels of anisotropy of velocities and delays are almost equal in each structure. The strongest anisotropy of delays and velocities (-4,5) is observed in the ventricle muscle layer; the weakest (1,7)-in a specialized layer. The anisotropy of velocities and delays is the greater, the greater is the electrotone anisotropy. A new mechanism of extrasistole initiation (reentry) in the system homogenous by the membrane properties, but with anisotropy of intercellular bonds is considered.

Animals↗
PubMedDate not supplied

[Model of a passive 3-dimensional anisotropic syncytium as a continuous medium].

A model is being proposed for analysis passive electrical properties of the syncitium with anisotropy. In terms of the model the potential is expected to decay as approximately e-r/r with an increase of the distance, r, from a polarising electrode. Input resistance of the three-dimensional syncitium loosely depends upon the resistance of electrogenic membrane, and thus should be mainly accounted for by the resistances of the myoplasm and intercellular contacts.

Cell Fusion↗
PubMedDate not supplied

[The effect of acetylcholine on passive electrical properties and intercellular electrical communications in the sinoatrial node of the rabbit heart].

The effect of acetylcholine (ACH) on passive electric properties and intercellular coupling was studied using microelectrode technique in experiments on isolated preparations of the sinoatrial area of the rabbit's heart. The space constant of electrotonic decay (lambda delta) and input resistance (RBX) were measured. ACH was found to reduce lambda delta and increase RBX. Analysis of the experimental data, using the model of thin layer 3-dimensional syncytium, revealed that ACH of 10(-7) M, 10(-6) M and 10(-5) M increased the resistance of intracellular syncytium by factor of 1.25, 1.36 and 1.43, respectively, and decreased the resistance of the electrogenic membrane by factor of 1.13, 1.12 and 1.23, respectively. It is concluded that ACH increases the resistance of intercellular contacts in the sinoatrial node.

Acetylcholine↗
PubMedDate not supplied

[Age-related characteristics of the electrical activity of the cardiac fibers in the human embryo].

Transmembrane action potential and intercellular electric coupling have been studied in isolated heart during various stages of intrauterine growth of human embryos as well as in heart preparations of human adults. Formation of electrical properties of ventricular myocardium was slower than that of atrial fibres and was found to be fully completed in the first 14 weeks of intrauterine growth. Intercellular electrical coupling enhanced in the course of the embryonic development as indicated by a drop in the input resistance and an increase in electronic length.

Action Potentials↗
PubMedDate not supplied

[Pharmacological study of quaternary trimecaine derivatives].

It has been demonstrated in experiments on cats, rabbits, white rats and mice that the quaternary derivatives of trimecaine (QDT) produce a protective and antiarrhythmic action in atrial (acetylcholine and aconitine) and ventricular (aconitine and calcium chloride) fibrillation. The relationship has been found between the characteristics of the radical at the quaternary nitrogen atom and the antiarrhythmic activity of the QDT. The effect of the QDT on the electrophysiological parameters of the myocardium not on the hemodynamics have been examined. It has been shown that the QDT might be suggested for use as new antiarrhythmic agents.

Acetanilides↗
PubMedDate not supplied

[Intercellular coupling in the sinus node of the rabbit heart].

Passive electrical properties of SA node region of rabbit's heart were studied. Electrotonic anisotropism was characteristic of the entire SA node; anisotropism decreased moving from crista terminalis to interatrial septum. The input resistance, RBX, was the largest in the region of true pacemakers and decreased moving to the perinodal region. Analysis of the results yielded specific resistance values for contacts and electrogenic membrane of 3 Ohms-cm3 and 10(4) Ohms-cm2 respectively.

Animals↗
PubMedDate not supplied

[Passive electrical properties of the atrioventricular region of the rabbit heart].

Passive electrical properties of AV node region of rabbit's heart were studied. Electrotonic anisotropism (a9) was characteristic of the entire AV node. a9 was the largest in the region of entry from the crista terminalis and in the lower node. The input resistance, RBX, of AV node was 1.3 to two-fold that measured in atrial trabeculae. Analysis of the results yielded the following specific resistance values for midnodal region: 1 Ohm--cm2 for contacts, 1200 Ohms-cm for intracellular space and 1300 Ohms-cm2 for electrogenic membrane. The nature of intercellular interaction and AV delay is discussed on the basis of the results obtained.

Animals↗