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At least 325 records · Page 18Linked to original sources
PubMed1994

The electrophysiological effects of dicentrine on the conduction system of rabbit heart.

1. The electrophysiological effects of dicentrine, an aporphine alkaloid isolated from the root of Lindera megaphylla, were examined in the Langendorff perfused rabbit heart and rabbit isolated cardiac cells. 2. Standard electrophysiological characters were measured in the Langendorff perfused rabbit heart (control study) and after 5 min exposure to 1, 3 and 9 microM of dicentrine and during the subsequent recovery phase sequentially (n = 7). The same study protocols were performed in 0.5 to 4.5 microM quinidine (n = 7), 18 to 162 microM procainamide and N-acetylprocainamide (n = 7) for comparison. 3. The results showed that the spontaneously beating heart rate and the sinoatrial (SA) and atrioventricular nodal (AH) conduction time were not significantly affected by dicentrine but were significantly suppressed by the higher doses of quinidine (4.5 microM) and procainamide (162 microM). 4. The His-Purkinje conduction time was significantly increased by the higher dose of dicentrine, quinidine and procainamide. 5. The ventricular repolarization time and its effective refractory period were significantly increased by the higher dose of dicentrine and the other agents. 6. The effective refractory period of the atrium, AV node and His-Purkinje system were also significantly increased by dicentrine and the other agents. 7. A voltage clamp study revealed that the prolongation of atrial action potential duration by dicentrine (9 microM) was associated with a significant inhibition of the transient potassium outward current. As well as inhibition of the transient outward current, a significant inhibition of the sodium inward current by dicentrine was found. 8.We conclude that (1) dicentrine is potentially a useful antiarrhythmic agent with type Ia and type III antiarrhythmic action; (2) the relative potency of dicentrine on the electrophysiological function of cardiac tissue is 10-20 times more than that of procainamide.

Action Potentials↗
PubMed1977

[Possibility of studying the specific stimulation-conduction system of the heart].

The author carried out a survey on a new method for functional diagnostics--recording of the Hiss bundle potentials. The investigation method is described as well as the normal values of electrogram of the Hiss bundle. The clinical significance of the most important indications for the investigation are discussed, namely: 1. Various forms of atrio-ventricular and ventricular disorders of the stimulation-conductivity process. 2. Indistinct rhythm disorders. 3. Diagnostics of the paranodal stimulation conductivity. 4. Pharmacological studies.

Arrhythmias, Cardiac↗
PubMed1981

[New diagnostic method in arrhythmias and heart conduction disorders].

The authors developed a method for recording spike potentials of the heart conduction system from the body surface on a curve of differentially intensified spike potential (DISP). They examined 187 patients and 60 healthy persons. The spike potentials of the sinoatrial node, atria and the bundle of His recorded on the DISP curves coincide exactly in time with spike potentials on intracardiac ECG recorded by microcatheterization of the heart through the subclavian vein, which makes it possible to distinguish on the DISP curve reference points for determining conductivity on definite areas of the heart conduction system. DISP recording allows the diagnosis of conductivity disorders and atrial overloading, arrhythmias of the heart, the diagnosis of which cannot be made from the ordinary ECG. In some cases this method can substitute for intracardiac ECG.

Action Potentials↗
PubMed1987

Adenylate cyclase and guanylate cyclase activity in the conduction system of rabbit hearts.

In comparison to the working myocytes no remarkable differences in the localization of adenylate cyclase (AC) and guanylate cyclase (GC) were found. The sarcolemmal plasma membrane of the AV node and the Purkinje fibers was the main site of the activity of these two enzymes. GC activity was additionally found at peripheral junctional couplings. Stimulation by hormones and specific activators for both AC and GC was demonstrated with difficulty. The reasons may be more the cytochemical preparation technique than the specificity of the AC and GC in the conducting tissue.

Adenylyl Cyclases↗
PubMed1988

Proliferation and biosynthetic activities of myocytes from conductive system and working myocardium of the developing mouse heart. Light microscopic autoradiographic study.

Incorporation of 3H-thymidine, 3H-uridine and 3H-leucine into myocytes and their mitotic activity have been investigated in different compartments of the mouse heart conductive system (CS) and working myocardium (WM) at pre- and postnatal stages of development. On 15th and 18th d of embryogenesis, 3H-thymidine pulse and cumulative labelling indices (LI) of myocytes in the sinoatrial node (SAN), atrioventricular node (AVN) and His bundle (HB) were found to be 4 to 6 times lower than in WM (0.001 less than or equal to P less than or equal to 0.01). On 3rd to 9th d after birth LI remained decreased (0.001 less than or equal to P less than or equal to 0.05) in SAN while replicative activity of myocytes in AVN and HB approached that of both ventricular and atrial WM. Since 13th d after birth LI did not exceed 1% in all the compartments studied. In the prenatal period LI in SAN were higher than in AVN P less than or equal to 0.01), whereas in the postnatal one it was just the opposite (0.001 less than or equal to P less than or equal to 0.05). During cardiogenesis change of mitotic indices in WM and CS correlates with that of LI. Duration of cell cycle and its periods (G2, G2 + 1/2 M, S) estimated by curves of labeled mitoses, double-labelling technique with 14C-thymidine and 3H-thymidine and label "dilution" method differ slightly in myocytes from WM and CS. The latter incorporate 3H-uridine much less intensively at most stages of heart development compared with WM. At perinatal stages of cardiogenesis 3H-leucine labels CS myocytes somewhat weaker than WM ones until 8th d after birth when the labelling intensities in all cell types become similar. It can be concluded that on the whole CS myocytes from the developing mouse heart appear to be less active than those of WM concerning replication, transcription, and translation processes.

Aging↗
PubMed1996

The alpha3 isoform protein of the Na+, K(+)-ATPase is associated with the sites of cardiac and neuromuscular impulse transmission.

The alpha (catalytic) subunit of the Na+ pump (Na+, K(+)-ATPase) has three isoforms; alpha1 is ubiquitous, skeletal muscle expresses predominantly alpha2, and alpha3 has been localized to specific types of neurons and, possibly, to axonal processes. The alpha3 isoform mRNA is also expressed in the rat cardiac conduction system. Thus, we studied rat heart and quadriceps muscles by immunohistochemistry using isoform-specific antibodies to the Na+ pump alpha subunit and labeled alpha-bungarotoxin as a probe for the neuromuscular junction (NMJ). We found that alpha3 pump protein is localized to three sites important for impulse transmission: the junctional complex between cardiac myocytes, the heart conduction system, and the NMJ. Specifically, all levels of the conduction system expressed alpha3 immunoreactive protein, as assessed by two isoform-specific antibodies and histological conduction system markers. Specific expression at the junctional complex was confirmed by immuno-EM. Double-labeling and denervation analysis indicated that alpha3-positive areas in skeletal muscle were presynaptic and adjacent to postsynaptic bungarotoxin-positive regions, which had the classic morphology of NMJs. Thus, specific Na+,K(+)-ATPase pump isoforms may be adapted to maintenance of membrane potential and/or intracellular ion concentrations required for impulse transmission in both heart and presynaptic motor terminals contacting skeletal muscle.

Animals↗
PubMedDate not supplied

Modeling of the heart's ventricular conduction system using fractal geometry: spectral analysis of the QRS complex.

Many biological systems having one or more characteristics that remain constant over a wide range of scales may be considered self-similar or fractal. Geometrical and functional overview of the ventricular conduction system of the heart reveals that it shares structures common to a tree with repeatedly bifurcating "branches," decreasing in length with each generation. This system may further simplify by assuming that the bifurcating and decreasing process is the same at any generation, that is, the shortening factor and the angle of bifurcation are the same for each generation. Under these assumptions, the conduction system can be described as a fractal tree. A model of the heart's ventricles which consists of muscle cells and a fractal conduction system is described. The model is activated and the dipole potential generated by adjacent activated and resting cells is calculated to obtain a QRS complex. Analysis of the frequency spectrum of the QRS complex reveals that the simulated waveforms show an enhancement in the high frequency components as generations are added to the conduction system. It was also found that the QRS complex shows a form of an inverse power law, which was predicted by the fractal depolarization hypothesis, with a highly correlated straight line for a log-power versus log frequency plot with a slope of approximately -4. Similar results were obtained using real QRS data from healthy subjects.

Computer Simulation↗