Key result
Ouabain markedly inhibits cellular potassium influx only at low external potassium concentrations.
Why the study?
The effect of ouabain on potassium exchange rates in the mammalian heart was not fully understood.
May caution digitalis dosing in hypokalemia; leaves open compartment-specific K handling in human myocardium.
The effect of the digitalis glycoside, ouabain, on potassium exchange in the guinea pig heart in vitro was studied with the aid of K42. With modified Ringer's solution as a perfusate at 38 C, K was found to exchange at two rates in both washout and buildup studies. In vivo equilibration studies also suggested more than one rate of exchange. Ouabain, in vitro, effected inhibition of entrance of K into the slowly exchanging compartment, but did not affect influx into the fast compartment or efflux from the fast or slow compartments. The ouabain inhibition was seen at Ringer's K concentrations of 3.8–4.3 mEq/liter was equivocal at K concentrations of 5.0–5.5 mEq/ liter and absent at K concentrations of 7.0–7.5 mEq/liter. It was postulated that ouabain inhibition was directed toward the slowly exchanging fraction of intracellular potassium.
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Schreiber et al. (1961) studied Normal mammalian heart tissue (in vitro). Ouabain vs. Control (ouabain-free physiological Ringer's solution) was evaluated on Potassium (K42) cellular influx and exchange rate. Ouabain markedly inhibited potassium influx into the slowly exchanging cellular compartment, an effect that was present at low external potassium concentrations but absent at higher concentrations.
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