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Science 27 November 1964:
Vol. 146. no. 3648, pp. 1176 - 1177
DOI: 10.1126/science.146.3648.1176
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Articles

Heart Action Potential: Dependence on External Calcium and Sodium Ions

R. K. Orkand 1 and R. Niedergerke 1

1 Department of Biophysics, University College London, London, W.C.I

The height of the overshoot of the action potential recorded from frog ventricles is markedly less sensitive to lowering the external sodium concentration than predicted by the sodium-hypothesis of excitation, and it is surprisingly sensitive to changes in the external calcium concentration. These observations are explained by a mechanism in which there is competition between sodium and calcium ions, in the excitable membrane, for anionic sites which control the inward current of sodium ions at the crest of the action potential.


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