The action of a toxin from the sea anemone Anemonia sulcata upon Mammalian heart muscles.

The cardiac activity of toxin II, a basic polypeptide (m.w.: 4770) from the sea anemone Anemonia sulcata, was investigated in isolated electrically driven guinea-pig and rat auricles, Langendorff heart preparations of guinea-pigs and cat heart-lung preparations. Low concentrations of toxin II (2-100 nM) evoked a dose-dependent positive inotropic effect in the three different heart muscle preparations investigated. Higher concentrations of toxin II produced toxic symptoms like contracture and arrhythmia in auricles and atria (about 25 nM). In isolated cat hearts high toxin II concentrations (about 160 nM) caused unusual toxic symptoms such as long periods of ventricular fibrillation alternating with periods of normal cardiac activity. In rat and guinea-pig auricles as well as in Langendorff hearts of guinea-pigs the extent and rate of the positive inotropic effect induced by toxin II depended on the extracellular calcium concentration (0.45 to 2.7 mM). Toxin II did not alter the heart rate in spontaneously beating isolated cat hearts. In electrically driven guinea-pig auricles, the rate of the inotropic effect induced by toxin II was accelerated by increasing stimulation frequencies. Toxin II did not change the coronary flow in Langendorff heart preparations of guinea-pigs.