RADIOACTIVITY AND PHYSIOLOGICAL ACTION OF 



POTASSIUM. 



By ROBERT F. LOEB. 

 (From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, August 15, 1920.) 

 I. INTRODUCTION. 



The cations Na, K, and Ca are essential constituents of physiologi- 

 cally balanced salt solutions such as blood serum, tissue fluids, and sea 

 water, and, in the absence of one of these ions, physiological processes 

 cannot, as a rule, occur for any great period of time. Zwaardemaker^ 

 has recently advanced the interesting idea that the indispensability 

 of potassium in cardiac action is due to the slight radioactivity of 

 that element. To prove this idea, he has demonstrated that other 

 radioactive substances, e.g. thorium, uranium, ionium, radium, etc., 

 can replace the K ion in restoring heart beat after the heart has 

 stopped beating in a Ringer solution containing no potassium. The 

 most significant fact demonstrated by Zwaardemaker and his collab- 

 orators is that for the replacement of potassium by other radioactive 

 substances, equiradioactive doses are required. Zwaardemaker's 

 conclusion that the action of potassium in physiologically balanced 

 salt solutions is a result of its radioactivity is of such great importance 

 that it seemed justifiable to test the applicability of this view to 

 physiological processes other than the heart beat. 



As a result of experiments by Herbst^ and others, it is known that 

 sea urchin eggs are unable to develop when placed in potassium-free 

 sea water immediately after fertilization, and Herbst found that rubid- 

 ium and cesium could replace potassium to a limited extent. It 

 seemed to us that a further study of the replacement of K by cesium 



^ Zwaardemaker, H., /. Physiol, 1919-20, liii, 273. 

 ^ Herbst, C, Arch. Entwcklngsmechn. Organ., 1901, xi, 617. 



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