Effect of Certain Cations on Relaxation of the Glycerol-Extracted Heart Muscle of Frogs

¹ From the Cardiovascular Division, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri

Hearts of large bullfrogs (Rana catesbiana) were extracted in 50% glycerol at –10 to –20°C. These hearts were then perfused with solutions of desired molarity, and contractions were measured by a compound lever attached to the ventricles. Perfusion was carried out with solutions containing magnesium, sodium, potassium or calcium chloride (using the molarities of these ions in Ringer's solution); the solutions were adjusted to ph 7.5 at room temperature. The salts were perfused singly or in various combinations. Ventricular contraction was induced by ATP (0.016 m, adjusted to ph 7.5) added directly to the perfusate. The data indicate that, following contraction of the hearts with ATP, the perfusion of Na, Mg and K cations enhance relaxation of the glycerinated hearts. Of these cations, the Na ion may be of particular importance in relaxation of the ATP-contracted muscle, for Na perfused alone caused a more rapid rate of muscle elongation. However, when the hearts were previously irrigated with Mg ion, perfusion with Na then provoked strikingly rapid relaxation of the glycerinated hearts. Ca ion was not observed to recontract the hearts after original ATP-contraction and relaxation by Na-Mg irrigation.