THE RELATION OF THE SODIUM, POTASSIUM, AND CALCIUM IONS TO THE HEART RHYTHMICITY

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Abstract
When the isolated sinus of the terrapin heart is brought to complete rest by continued perfusion with isotonic solution of dextrose, rhythmic activity, both electrical and mechanical, although usually small, may be restored for a period by perfusion with solutions containing only NaCl. Solutions containing only Ca or K salts, or a combination of the 2, have no such effect. Na seems, therefore, to contribute the essential factor in the production of an inner stimulus. The Ca ion appears to be essential to the production of strong, functionally effective mechanical contractions. K ions have no specific function in releasing the internal stimulus of the heart; they seem rather to regulate the interaction between the Na and Ca ions. In the washed frog''s heart, there is a distinct antagonism between Na and Ca in their effect upon rhythmicity. Solutions containing NaCl alone permit or produce rhythmic responses, while the addition of CaCl2, in physiological concentrations, inhibits all rhythmic activity, so far as can be judged by the electrical and mechanical responses. In the auricle and ventricle of the terrapin the addition of Ca to the Na solution does not seem to inhibit rhythmicity although some evidence of this antagonistic effect appears in the terrapin sinus. A rhythmical electrical beat may be exhibited by heart muscle in complete absence of any mechanical beat. Such a condition occurs after prolonged perfusion with a solution containing Na and K or Na alone, i.e., in the absence of Ca.

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