Effect of ouabain on Ca⁴⁵ and Cl³⁶ exchange in isolated rabbit atria

¹ Department of Pharmacology, University of Mississippi Medical Center, Jackson, Mississippi

The effect of ouabain (1 x 10^–6 m) on Ca⁴⁵ and Cl³⁶ exchange in isolated atria has been investigated. Ouabain increases Ca⁴⁵ influx, but has no effect on efflux. The action on influx is enhanced by an increase of Ca and blocked by an increase of K in the medium. These findings are interpreted to mean that the systolic action of ouabain results from an increase of Ca in the membrane or myoplasm. It is suggested that the known actions of cardiac glycosides on active transport of Na and K are secondary to this action on influx. Ouabain also increased Cl³⁶ influx, having no action Cl³⁶ efflux. This finding suggests that ouabain may increase passive membrane permeability.