Potassium and Sodium Exchange in the Working Frog Heart Effects of Overwork, External Concentrations of Potassium and Ouabain

¹ From the Radioisotope Service, Veterans Administration Hospital, Bronx, New York

Potassium and sodium exchange was studied in vitro in the working frog heart with the use of the radioactive isotopes K⁴² and Na²⁴. Measurement of loss or gain of radioactivity, and hence the outflux or influx of the cations, is accomplished by placing a test tube containing the continuously perfused preparation into the well of a scintillation counter. Intracellular potassium in the working ventricle exists in two phases or components which exchange at different rates. The slowly exchanging phase is sensitive to the amount of work performed, external concentrations of K and failure of the contractile mechanism. The digitalis glycoside, ouabain, causes an inhibition of entrance of potassium into the slowly exchanging phase, while the fast component exchanges freely. It is suggested that the two phases of potassium exchange exist in parallel within the cell, and that potassium exchanges freely across a nonlimiting membrane.

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