The Experts below are selected from a list of 3447 Experts worldwide ranked by ideXlab platform

Ronald M Harriswarrick - One of the best experts on this subject based on the ideXlab platform.

H Soustre - One of the best experts on this subject based on the ideXlab platform.

  • forskolin effects on Slow Inward Current and phasic tension of frog atrial fibres modulation by adenosine and phosphodiesterase inhibitors
    European Journal of Pharmacology, 1992
    Co-Authors: C Gauthier, H Soustre
    Abstract:

    Abstract The effects of forskolin, which is known as a direct activator of adenylate cyclase were studied on the Slow Inward calcium Current (Isi) and phasic tension of frog atrial fibres. Forskolin induced a dose-dependent positive inotropic effect related to an increase in the Slow Inward calcium Current. These effects, which were not reproduced by 1,9-dideoxyforskolin, seemed to result from an activation of adenylate cyclase. The action of forskolin was antagonized by adenosine and potentiated by phosphodiesterase inhibitors with the following order of potency: rolipram > theophylline > dipyridamole; M & B 22,948 was without influence. This study suggests that adenosine and rolipram might be suitable tools for studying the implication of cAMP in the modulation of contraction in frog atrium.

  • theophylline effects on phasic tension and Slow Inward Current of isolated frog atrial fibres influence on the action of isoprenaline
    Pharmacology & Toxicology, 1991
    Co-Authors: C Gauthier, H Soustre
    Abstract:

    The action of theophylline on phasic tension and Slow Inward Current (Isi) was investigated on isolated voltaged-clamped frog atrial fibres. The action of theophylline was both dose- and time-dependent; the most effective dose was 2.10(-3)M. Theophylline induced a rapid positive inotropic effect which cannot be attributed to a beta-adrenoceptor stimulation or to an adenosine antagonism; this effect was closely related to an increase in Slow Inward Current (Isi), probably due to an inhibition of phosphodiesterase activity and a subsequent increase in cAMP content. The decline of the positive inotropic effect of theophylline was discussed in terms of additional effects of the drug. Theophylline, consistently with its phosphodiesterase inhibitory action, was shown to potentiate the effects of isoprenaline on phasic tension and Isi; however no potentiation was observed after reserpine-induced depletion of endogenous catecholamines. It might be thought that non-specific effects of reserpine on some steps of cardiac excitation-contraction coupling counteract the effects of theophylline.

Mingxing Jiang - One of the best experts on this subject based on the ideXlab platform.

  • effects of linesinine on Slow action potentials in myocardium and Slow Inward Current in canine cardiac purkinje fibers
    Acta pharmaceutica Sinica, 1993
    Co-Authors: J L Wang, Y Nong, Guojin Xia, W X Yao, Mingxing Jiang
    Abstract:

    Standard microelectrode and two-microelectrodes voltage clamp techniques were used to study the effects of linesinine (Lien), an alkaloid extracted from the green seed embryo of Nelumbo nucifera Gaertn, on Slow action potentials (AP) and Slow Inward Current (Isi). Lien 10-100 mumol/L was shown to concentration-dependently decrease the action potential amplitude (APA), the maximal velocity of phase 0 depolarization (Vmax) and prolong the sinus cycle length (SCL) of Slow AP in isolated sinoatrial node (SAN) pacemaker cells of rabbits. On both Slow APs of rabbit SAN cells and guinea pig papillary muscles partly depolarized by high K+, Bay K 8644 0.03 mumol/L markedly increased the APA and Vmax, which were obviously antagonized by Lien 10 mumol/L. Moreover, Lien 1-100 mumol/L was found to inhibit the Isi of canine cardiac Purkinje fiber in concentration-dependent manner. Lien 3 and 100 mumol/L reduced the peak value of Isi by 14% and 88% respectively. The results suggest that Lien possesses calcium antagonistic effects.

M. Šimurdová - One of the best experts on this subject based on the ideXlab platform.

  • Voltage dependence of force- and Slow Inward Current restitution in ventricular muscle
    Basic Research in Cardiology, 1992
    Co-Authors: P. Bravený, J. Šimurda, M. Šimurdová
    Abstract:

    This study was aimed to assess the relationship among the voltage-dependent processes underlying the excitation-contraction coupling, viz. force restitution (FR), transmembrane Ca fluxes and Ca release. The experiments (n=22) were performed on voltage-clamped dog trabeculae in which force and Slow Inward Current were measured. Standard steady-state was achieved by clamp driving at 0.5 Hz, 300 ms, 70 mV depolarizing pulses from holding=resting potential at 30°C. Voltage and duration of single pulses and intervals in between were varied according to five protocols. The voltage dependence of Ca release was tested by varying single pulses at equal steady-state, i.e., at equal Ca availability. Contractions could be elicited in absence of I_Ca (20–30 mV step) and in the presence of disproportionately small I_Ca (above 80 mV). The voltage dependence of Ca availability for the release was tested by constant test pulses following either a variable conditioning clamp pulse or a period of rest at a variable voltage. After a low voltage pulse and, hence, depressed or absent I_Ca, the test contraction is diminished in presence of normal or even augmented I_si at any test interval (i.e., FR is depressed). Diminished Ca influx thus reduces the Ca availability of the subsequent beat. During prolonged depolarization (by 60 mV and more) a tonic response appears, but a phasic response cannot be elicited (FR is inhibited). Upon subsequent repolarization FR starts from zero and is significantly enhanced. It is concluded that, during depolarization, Ca release channels are in an open state, thus allowing free recirculation of Ca, but no build-up of a sufficient Ca gradient at the release site.

Bing Zhang - One of the best experts on this subject based on the ideXlab platform.