1970 年 11 巻 3 号 p. 269-290
By altering the calcium, sodium and potassium content of the Tyrode solution, the relationship between the shape of the action potential and of the contraction curve in regard to the changes induced by l-isoproterenol, dl-norepinephrine and ouabain, and at the same time the mode of action of these drugs were sought for. In the normal Tyrode solution, shortening of the duration of the action potential at 25% and 50% repolarization showed a significant correlation with the increment of the contractile force, and the total duration of the action potential showed a significant correlation with the time to the peak tension and with the total duration of the contraction curve at the maximal effect period of these drugs. This relationship was found to be more or less true qualitatively also when the extracellular ions were altered variously.
By analyzing the observed changes, it was concluded that l-isoproterenol increases the contraction, employing chiefly the extracellular calcium ions, whereas dl-norepinephrine and ouabain can increase the contraction by mobilizing in addition the intracellular calcium ions in a calcium-free solution. The increase of contraction by l-isoproterenol is mostly independent of the potassiumion, whereas that by ouabain and dl-norepinephrine occurs in connection with this ion. l-Isoproterenol and dl-norepinephrine increase the contraction directly by driving the calcium ions into the cell rather than by exchanging the sodium ions with the calcium ions. The inotropic action of ouabain does not seem to have any relation with either the sodium ions or the calcium ions entering at this phase.
