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Updated: Oct 2, 2026

Assessment of Sarcoplasmic Reticulum Calcium Reserve and Intracellular Diastolic Calcium Removal in Isolated Ventricular Cardiomyocytes
Published on: September 18, 2017
The Na+-Ca2+ exchanger is essential for the action of cardiac glycosides
Hannes Reuter1, Scott A Henderson, Tieyan Han
1Department of Physiology, UCLA School of Medicine, Los Angeles, Calif 90095-1760, USA.
Abstract:
The widely accepted model to explain the positive inotropic effect of cardiac glycosides invokes altered Na+-Ca2+ exchange activity secondary to Na+ pump inhibition. However, proof of this model is lacking and alternative mechanisms have been proposed. We directly tested the role of the Na+-Ca2+ exchanger in the action of the glycoside ouabain using Na+-Ca2+ exchanger knockout mice. Ablation of the exchanger is embryonic lethal, but contractility can be studied in embryonic heart tubes at day 9.5 postcoitum. Heart tubes isolated from homozygous Na+-Ca2+ exchanger knockout mice (NCX-/-) display surprisingly normal Ca2+ transients. Removal of extracellular Na+ induces Ca2+ overload in wild-type heart tubes but does not alter the Ca2+ transients of NCX-/- heart tubes. Similarly, ouabain, at levels causing Ca2+ overload in wild-type heart tubes, has no effect on NCX-/- heart tubes. We conclude that in embryonic mouse myocytes the Na+-Ca2+ exchanger is absolutely required for the effect of cardiac glycosides on Ca2+(i).
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