Post-extrasystolic potentiation; effect of Ca, histamine, caffeine and epinephrine.

The influence of caffeine, epinephrine, histamine and high Ca solutions on post-extrasystolic potentiation of guinea-pig's isolated heart muscle was investigated. It was found that caffeine suppressed the potentiation process while epinephrine and high Ca solutions enhanced it. Histamine caused a gradual decrease in post-extrasystolic potentiation.

Passive electrical properties of the atrio-ventricular node.

The passive electrical properties of the atrioventricular node and of the atrial muscle of the rabbit heart were determined. To polarize the cells, a small suction electrode was used. The space constant of the atrio-ventricular node was found to be small (430 micron) compared to other cardiac fibers.

Effect of phosphodiesterase inhibitors and dBcAMP on the inotropic and relaxing actions of histamine in cardiac muscle.

The influence of phosphodiesterase inhibitors, imidazole and dBcAMP on the action of histamine on peak tension, on rate of tension development and rate of relaxation of ventricular muscle of guinea pig's heart was investigated. It was found that theophylline plus dBcAMP enhanced the peak tension, (dF/dt)max and the rate of relaxation and increased the relaxing action of histamine. Imidazole, an activator of phosphodiesterase, also potentiated the action of histamine on peak tension, (dF/dt)max and rate of relaxation.

Influence of the sodium pump on intercellular communication in heart fibres: effect of intracellular injection of sodium ion on electrical coupling.

1. The effect of intracellular sodium injection on the electrical coupling between cardiac Purkinje cells was investigated. 2.

Sodium pump: its importance to intercellular communication in heart fibres.

The effect of ouabain on the electrical coupling of canine Purkinje cells was investigated. It was found that the glycoside decreases cell communication through an increase in junctional resistance, what supports the view that the sodium pump has an important role on the control of cell communication.

On the mechanism of histamine action in cardiac muscle.

The effect of histamine on electrical and mechanical properties of guinea-pig ventricular muscle fibers was investigated. It was found that the drug decreased in rate of tension development, the rate of fall of the twitch and decreased the time to peak tension. The height of the plateau of the action potential was increased by histamine and this seems to explain, at least, part of the drug action on heart contractility.

Effect of intracellular injection of calcium and strontium on cell communication in heart.

1. The influence of Ca and Sr on the electrical coupling of canine Purkinje cells was investigated by injecting the ions electrophoretically into the cytoplasm. 2.