1,721,031 research outputs found
Interazione elettrotonica delle cellule del nodo seno-atriale
No full textPreparati di atrio di coniglio (regione del nodo seno-atriale) sono stati perfusi con soluzioni Tyrode ipertoniche (500 mM/l), o con soluzioni Tyrode a temperatura di 26 °C. In entrambe queste due situazioni sperimentali, il preparato presenta due o più foci autoritmici a diversa frequenza che interferiscono tra loro. Uno dei foci è sempre localizzato al di sopra della "crista terminalis" e corrisponde a una regione del nodo del seno dalla quale, nel preparato in Tyrode normale a 37 °C gli impulsi si propagano alla crista terminalis e attivano le fibre muscolari atriali. Da questa regione si sono registrati con microelettrodi oscillazioni lente del potenziale di membrana di forma sinusoidale in cui la fase di depolarizzazione diastolica non trapassa gradualmente nella fase di salita del potenziale di azione. L'ampiezza delle oscillazioni varia col variare dell'estensione dell'area di cellule autoscillanti sincrone. La forma delle oscillazioni può modificarsi per il sovrapporsi di onde sfasate provenienti da focus vicini. I tracciati dimostrerebbero l'interferenza elettrotonica delle cellule contigue ed il fatto che l'oscillazione lenta di base registrata da una cellula è il risultato della integrazione dei segnali del pool di cellule sincrone
Electrophysiological aspects of the action of bunaphtide on single cardiac muscle fibres
No full textThe action of Bunaphtide N (2-diethylamine-ethyl) N(n-butyl)-α-Naphtamide, a new antiarrhythmic compound, has been studied on single cardiac muscle fibres. Electrophysiological aspects have been considered, comparing action potentials recorded from single cardiac fibres perfused in Tyrode and Tyrode+Bunaphtide (24 γ/1 - 1000 γ/1). Experiments have been carried out on atrial cells, Purkinje fibres and papillary muscles. Idioventricular rhythm has been obtained from papillary muscles preparations where ectopic centre has been brought into action. In the atrial zones drug reduces the duration of the action potential within the first 30 sec of contact; after 10 min of perfusion, however Bunaphtide caused a significant lengthening. Rate was reduced by 20-25%. An increase (18%) in amplitude of the potential (hyperpolarisation) has been observed. In cells contiguous to the sino-atrial pacemaker (not real pacemaker zones) and in ectopic centre, effect of Bunaphtide consisted of reducing the level of the potential, damping the slow subliminal oscillations of membrane resting potentials
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effetti del C3 sul potenziale d’azione della cellula cardiaca : risultati preliminari
No full textGli Autori hanno studiato gli effetti elettrofisiologici del C3 sul potenziale d’azione della singola cellula cardiaca (lucertola, cavia e coniglio), in particolare sulle cellule atriali di miocardio comune, sulle cellule del muscolo papillare e infine sulle cellule del sistema His-Purkinje. Le azioni elettrofisiologiche possono essere così sintetizzate: iperpolarizzazione della membrana cellulare; aumento della durata del potenziale d’azione; lieve riduzione della velocità di salita del potenziale d’azione (dV/dt); effetto cronotropo positivo. Il C3 inoltre accorcia la durata della fase 4 di depolarizzazione diastolica (= potenziale pace-maker) e favorisce la comparsa di una depolarizzazione diastolica lenta trasmessa elettrotonicamente dalle cellule segnapassi, in fibre del muscolo papillare del cuore di coniglio rese autoritmiche in seguito a stimolazione. I dati sperimentali potrebbero essere coerenti con un’azione antiaritmica del farmaco, che si mostrerebbe capace di interrompere disordini legati al fenomeno del “rientro”. Inoltre la conduzione degli impulsi verrebbe facilitata e non ostacolata, grazie all’effetto iperpolarizzazione ed all’azione di accelerazione lieve del potenziale pace-maker. In termini di conduttanza di membrana al potassio, il C3 potrebbe esplicare talune sue azioni elettrofisiologiche attraverso una riduzione della permeabilità di membrana al K+.Effects of C3 on the action potentials of the myocardial cell. Preliminary results. –The Authors have investigated the electrophysiological effects of C3 on the action potential of the heart cell (in lizard, guinea-pig, and rabbits), of the atrium, of papillary muscle and of the His-Purkinje system. The electrophysiological effects of C3 can be summarized as follows: hyperpolarization of the cell membrane, longer duration of the action potential, slight reduction of the rate of rise of the action potential (dV/dt), positive chronotropic effect. Furthermore, C3 shortens the length of the phase 4 of diastolic polarization (i.e., the pacemaker potential) and favours the occurrence of slow diastolic depolarization, the latter being electrotonically transmitted by cells in the papillary muscle fibers of rabbit heart which were made self-rhythmic through stimulation. The experimental data might be consistent with an antiarrhythmic effect of the drug. In fact, it seems to succeed in stopping disorders connected with the so-called “re-entry” phenomenon. Moreover, action potential propagation is supposed to be improved rather than hindered by the drug’s hyperpolarizing effect and by the slight speeding-up influence on the pacemaker potential. In terms of potassium conductance through the cell membrane, C3 might exert some electrophysiological effect by reducing the membrane permeability to K+
Microfungal biodeterioration of historic paper: Preliminary FTIR and microbiological analyses
No full textInfluence of ouabain on the spontaneous oscillations frequency in cardiac pacemaker
No full textThe behaviour of true-pacemaker cells of rabbit-heart has been analyzed in presence of various concentrations of ouabain, to verify the influence of active transport on the spontaneous oscillations. Curves of frequency f via temperature T of bathing solution have been deduced. The results obtained show that ouabain in the concentration range 10-7-5*10-5 mM/l influences both the parameters of regression lines f (T): precisely there is an increase in slope and absolute frequency values in the temperature range 28-38 °C. We have also observed that a temperature increase causes an increase of maximum diastolic potential (MDP), however the overshoot values remain unmodified. These results agree with the hypothesis that a metabolic activity, as active transport across membrane, influences the mechanism of pacemaker spiking generation
Influenza della ouabaina sulla frequenza di oscillazione spontanea del pacemaker cardiaco, e sulla attività sincrona
No full textÈ stato analizzato il comportamento delle cellule vere-pacemaker del cuore di coniglio in presenza di varie concentrazioni di ouabaina allo scopo di verificare l’influenza di un trasporto attivo ionico sulla oscillazione (massimo potenziale diastolico) e la frequenza delle oscillazioni in cellule del pacemaker. In particolare, sono state rilevate le curve della frequenza in funzione della temperatura della soluzione perfondente in presenza ed in assenza di ouabaina. Inoltre, si sono fatte registrazioni continue dei potenziali d’azione di una cellula perfusa in Tyrode e Tyrode + ouabaina misurando la massima iperpolarizzazione della cellula durante l’oscillazione spontanea e l’effetto del farmaco sull’attività sincrona del pool in funzione del tempo di perfusione in Tyrode + ouabaina a temperatura costante, flusso costante e concentrazione (costante) del farmaco. I risultati ottenuti indicano che la ouabaina in concentrazione di 10-7-5·10-5 mM/l influenzano ambedue i parametri della retta f (T°) e precisamente si ha un aumento della pendenza e dei valori assoluti della frequenza nell’ambito delle temperature analizzate (28 °C-38 °C)
Properties of the hyperpolarizing-activated current (if) in cells isolated from the rabbit sino-atrial node
Full text linkIndividual cells were isolated from the sino-atrial node area of the rabbit heart using an enzyme medium containing collagenase and elastase. After enzymatic treatment the cells were placed in normal Tyrode solution, where beating resumed in a fraction of them. Isolated cells were studied in the whole cell configuration. Action potentials as well as membrane currents under voltage-clamp conditions were similar to those in multicellular preparations. Pulses to voltages more negative than about -50 mV caused activation of the hyperpolarizing-activated current, if. Investigation of the properties of this current was carried out under conditions that limited the influence of other current systems during voltage clamp. The if current activation range usually extended approximately from -50 to -100 mV, but varied from cell to cell. In several cases, pulsing to the region of -40 mV elicited a sizeable if. Both current activation and deactivation during voltage steps had S-shaped time courses. A high variability was however observed in the sigmoidal behaviour of if kinetics. Plots of the fully-activated current-voltage (I-V) relation in different extracellular Na and K concentrations showed that both ions carry the current if. While changes in the external Na concentration caused the current I-V relation to undergo simple shifts along the voltage axis, changes in extracellular K concentration were also associated with changes in its slope. Again, a large variability was observed in the increase of I-V slope on raising the external K concentration. The current if was strongly depressed by Cs, and the block induced by 5 mM-Cs was markedly voltage dependent. Adrenaline (1-5 microM) and noradrenaline (1 microM) increased the current if around the half-activation voltage range and accelerated its activation at more negative voltages. Often, however, drug application failed to elicit any modification of if. Current run-down was observed in nearly all cells, although at a highly variable rate. It was accelerated by raising the extracellular K concentration but did not show a marked use dependence. Both the if activation curve and the fully activated I-V relation were affected by run-down, the former being shifted to more negative values along the voltage axis and the latter being depressed with no apparent change of the if reversal potential
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