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Biomedical subjects

F F Bukauskas

Publications and source records attributed to F F Bukauskas.

At least 37 records · Page 2Linked to original sources
PubMed1993

Multiple conductance states of newly formed single gap junction channels between insect cells.

Two cells of an insect cell line (Aedes albopictus, clone C6/36) were pushed together to form a cell pair while the intercellular current flow was monitored. This approach enabled us to study the formation of gap junction channels and explore their electrical properties. We found that the single channels exhibit multiple conductance states. The conductance of a fully open channel was 365 pS; the subconductance steps were 1/7 to 1/5 of the maximal conductance. The voltage gradient across the junction did not influence the conductance of fully open channels, but affected the dwell time at particular conductance states. The latter provides an explanation for the voltage-dependent conductance of gap junction membranes seen in these cells. The very first channel opening always was slow (15-50 ms), suggesting the involvement of a mechanism different from conventional channel gating.

Aedes↗
PubMed1992

Effect of transmural vagal stimulation on electrotonic current spread in the rabbit sinoatrial node.

OBJECTIVE: The effect of vagal stimulation on the decay of electrotonic potential caused by intracellular current injection and on input resistance was measured in the sinoatrial node of isolated rabbit right atria. METHODS: Studies were performed on New Zealand White rabbits weighing approximately 2-3 kg. Vagal stimulation was achieved by transmural stimulation of intramural nerve fibres in the presence of propranolol. A K+ perfused suction electrode was used to inject hyperpolarising current pulses; input resistance was measured by means of a double barrel microelectrode. RESULTS: Vagal stimulation which caused a 14-20% increase of cycle length diminished electronic potential significantly by a decrease of membrane resistance. The input resistance of the sinoatrial node was not affected. Space constant values calculated by using either a one or a two dimensional model of electrotonic current spread were decreased on average by 13% and 14% respectively. CONCLUSIONS: The results from this study show that vagal stimulation which gave rise to a moderate negative chronotropic effect and marked changes in action potential configuration of nodal fibres affects the electrotonic interaction within the sinoatrial node. This may have consequences for the electrical activity and synchronisation of the sinoatrial nodal fibres.

Action Potentials↗
PubMed1992

Cytoplasmic bridges and gap junctions in an insect cell line (Aedes albopictus).

Cell pairs of an insect cell line (Aedes albopictus, clone C6/36) were used study simultaneously the diffusional and electrical properties of intercellular junctions. Diffusion studies involved injection of fluorescent molecules into one cell of a cell pair and visual inspection of their intercellular redistribution. Electrical measurements involved a dual voltage clamp method and whole-cell recording with patch pipette. The voltage clamp protocol was aimed at examining the dependency of the junctional conductance, gj, on membrane potential, Vm. Cell pairs exhibiting a voltage-dependent gj were found to allow intercellular diffusion of Lucifer Yellow CH (molecular mass, 443 Da), but not of FITC-dextran (molecular mass, 4,400 Da). This response pattern is consistent with the presence of gap junctions in the intercellular junctions. Cell pairs showing no voltage dependence of gj were found to permit intercellular diffusion of both Lucifer Yellow CH and FITC-dextran (dextran labelled with fluorescein isothiocyanate). This behaviour is compatible with the presence of cytoplasmic bridges connecting the two adjacent cells. Hence, in culture the cells investigated express two kinds of intercellular structures, gap junctions and cytoplasmic bridges.

Aedes↗
PubMed1991

[Experimental analysis of the formation of macro-reentry in the right atrium of rabbits].

The aim of the present study was experimental demonstration of the formation of reentry in isolated preparations of the rabbit's right atrium, including sulcus terminalis, interatrial septum and AV node. Tachycardia was evoked by extrasystolic stimulation of the preparation. Reentry was identified by computerized multichannel mapping of excitation wave propagation. A series of sections performed in the area between the caval veins and the coronary sinus confirmed the presence of reentry pathway round the orifices of caval veins and through AV made zone. Local cooling and sections performed in different parts of the AV node showed that not all areas of AV node were involved in the formation of reentry, but only the perinodal (AN) area. These effects on the AN area terminated tachycardia. Linear dependence between the period of tachycardia and delay in the AV nodal zone was found.

Animals↗
PubMed1990

Phase dependency of electrotonic spread of hyperpolarizing current pulses in the rabbit sinoatrial node.

Electrotonic current spread in the SA node of the rabbit was measured by means of hyperpolarizing current pulses (1 to 10 microA, 60 ms), which were injected intracellularly through a K(+)-perfused suction electrode. The pulses were applied at the beginning, middle or end of the diastolic depolarization phase. The resulting membrane potential change of nodal fibers was measured with microelectrodes. Space constants were calculated by fitting single exponential curves to the data. The input resistance (Rin) of fibers at different sites in the SA node was measured by means of a double barrel microelectrode (current pulses 5.5 to 11 nA, 60 ms) to detect a change in the internal resistance during the diastolic depolarization phase. During diastole the average electrotonic potential increased by 30% (P less than 0.001), the increase of the space constant ranged from 9 to 183% (P less than 0.05). Rin however, did not change during diastole. It is concluded that the electrotonic spread increased phase dependently, due to an increase of membrane resistance; the internal resistance was not phase dependent.

Animals↗
PubMed1989

Anisotropy of electrotonus in the sinoatrial node of the rabbit heart.

In fibers of the sinoatrial node of isolated right atria of rabbits the decay of the electrotonic potential caused by intracellular current injection was measured in two directions: parallel to the crista terminalis and perpendicular to it. A K+-perfused extracellular suction electrode was used to apply current pulses (10(-5) A, 60 ms) to fibers located in the primary center of the SA node every fourth cardiac cycle at a fixed moment during diastole. The decay of the electrotonic spread was measured in a series of impalements on a straight line from the current source. Space constants were calculated by fitting single exponential curves to the data. Considerable regional differences in space constant values were found in either direction. Parallel to the crista terminalis the mean value was 529 +/- 446 microns (S.D., n = 7), perpendicular to it 306 +/- 295 microns (n = 12); the difference was not significant (P less than 0.2). However, a significant anisotropy (P less than 0.05) of the electrotonic spread was found when measurements were taken from small areas of the node. Large abrupt changes in the electrotonic potential within 200 microns were observed in the center of the node. These data indicate a non-uniformity of electrotonic spread in this part of the SA node.

Animals↗
PubMed1987

[Transposition of the pacemaker in the right atrium during stimulation of the vagus nerve in the dog].

The heart rate and intraatrial latencies between epicardial electrograms from three sites of the right atrium have been studied during vagal stimulation in open-chest dogs. It has been shown that alterations of latencies started at a certain cardiac cycle length irrespective of pacing frequency. A transitional process of changes from a steady latency value in the control to another steady value during vagal stimulation has been observed. The transitional process has been simulated in experimental procedure in which two sites of the right atrium were paced at close and constant frequencies. To interpret the results obtained one-dimensional model of the sinus node has been constructed. According to the model, pacemaker shift within the sinus node results from a competition between two foci of automaticity with close intrinsic frequencies.

Animals↗
PubMed1987

[A method of determining the location of the pacemaker in the canine right atrium].

Theoretical calculations and experiments on hearts of open-chest dogs have demonstrated a possibility of localizing a spontaneous excitation focus by recording 2 intra-atrial delays representing differences in activation moments at 3 sites of the right atrium. Assuming myocardial homogeneity with respect to excitation spread velocity, it has been shown that the pacemaker can be localized by intersection of two hyperbola-like intra-atrial delay isochronisms with recording electrodes at their foci. In natural, i.e. nonhomogeneous myocardium, experiments have been conducted to simulate pacemakers with known co-ordinates by electrical stimulation of various sites within the right atrium. Comparison of experimental and theoretical data showed the present method to be able to localize the pacemaker with an error of +/- 3 mm, provided the pacemaker is between the recording electrodes where the intra-atrial delays do not exceed 60% of their maximum values.

Animals↗
PubMed1986

Cryosurgery in tachycardia treatment.

Cryosurgical techniques have become established and acceptable therapy in the treatment of resistant arrhythmias. In this report, both experimental and clinical data are presented describing the results of various cryosurgical techniques used at the Cardiac Rhythm Disturbance Center in Lithuania, USSR.

Animals↗
PubMed1985

[Use of differential methods for analyzing electrocardiograms in the diagnosis of supraventricular arrhythmia].

Differential-gain ECG (DG-ECG) recordings were made to investigate the mechanism of tachyarrhythmias. The study comprised experimental and clinical series. Experimental findings demonstrated two types (local and circulatory) of vulnerability manifested during induced tachyarrhythmia. Differential-gain ECG recordings were used in the clinical series to specify experimentally-demonstrated mechanisms of tachyarrhythmias: differentiate focal and circulatory excitation sources and specify the localization of both the sources of tachycardia and additional atrioventricular bundles associated with the ventricular pre-excitation syndrome.

Adult↗
PubMed1983

[Changes in the localization of the cardiac pacemaker in the rabbit sinus node during hyperkalemia].

Isolated preparations of the rabbit right atrium were studied by special techniques for changes in the localization of the cardiac pacemaker under conditions of elevated extracellular concentrations of potassium ions [K+]o. When [K+]o was 10.8 mM, the cardiac pacemaker moved from the superior to the inferior part of the sinus node (by 4-6 mm with 2-4 intermediate positions). Shifts in the position of the cardiac pacemaker were accompanied by changes in spontaneous contractions. They were also attended by changes in the pattern of the total electrogram of the preparation which was indicative of an altered electrical activation of the right atrium. It is noteworthy that these changes occurred only when the cardiac pacemaker shifted along the terminal crest. Perfusion by normal [K+]o-containing solution resulted in the migration of the pacemaker in the reversed direction, with the number of the intermediate positions rising to 3-5. The findings obtained point to a marked functional heterogeneity of the sinus node.

Action Potentials↗
PubMed1981

[Characteristics of the operations on the heart conduction system in the pre-excitation syndrome].

Observation of 13 patients with the septal location of additional conducting pathways is given, 2 of them had James' fibres, 1 had a combination of James' and Mahaim bundles, in the remainder the Kent's bundle was in the anterior position. Removal of conduction through Kent's and His' bundles is described in detail. The syndrome of pre-excitation was successfully removed in 10 out of 12 patients, 1 had relapses later and 2 died. A detailed analysis of all 35 operated on patients with the pre-excitation syndrome is given. Good results were obtained in 88.57%.

Adult↗
PubMed1981

[Characteristics of operations on the heart conduction pathways in the preexcitation syndrome. I. Destruction of the bundle of Kent in the free cardiac wall].

The authors describe the technique and the results of the operation of the dextra-located Kent's bundle in patients with the Wolff - Parkinson - White syndrome. In all 10 patients the interruption of the pathological conductivity was successful (1 patient was operated on again). In the left-sided localization in 8 out of 11 patients the stimulation syndrome was removed permanently, in 2 temporarily and in 1 the operation was unsuccessful. In 1 patient radio-frequency cardiostimulator has been grafted to stop the attacks.

Adolescent↗