Extracellular calcium concentration and calcium blocking agents on the action of ouabain on isolated rat atrium

Abstract

Summary The influences of calcium blocking agents and different[Ca 2+ ] o on the non toxic (positive inotropism without changes in frequency or resting tension) and toxic (positive chronotropism, negative inotropism, contracture, arrhythmia) effects of ousbain upon isolated rat stris were explored. Decreasing the [Ca 2 ] o from 1.2 to 0.3 mM or tresting the auricles with verapamil, D-600 or diltiazem potentisted the positive inotropic influences of ouabain and attenuated and delayed the onset of toxic actions. On the contrary increasing [Ca 2+ ] o from 1.2 to 2.7 mM, reduced the non toxic effect of ouabain and facilitated the toxic action of the drug. These findings suggest that factors known to induce changes in the intracellular calcium concentration (i.e. calcium blocking agents, and variable extracellular calcium concentrations) produce a remarkable modification of the influence of ouabain on rat myocardium.