INTRACELLULAR POTASSIUM— TAYLOR 27 



mic animal? Of the experiments cited, only those of Brues with chick embryonal 

 tissue, and of Raker, ct ol., with human erythrocytes have provided an indication 

 of the temperature below which loss of tissue potassium occurred. In both cases the 

 temperature was about 15°. The coincidence of this figure with the body tempera- 

 ture incompatible with survival in artificially chilled warm blooded animals sug- 

 gested a possible relation between these electrolyte shifts and the lethal effects of 

 hypothermia and led to the experiments which I shall describe. 



In the first experiments, hemidiaphragms from rats and from hamsters were 

 incubated in Krebs-Ringer-bicarbonate solutions containing glucose. Water baths set 

 at various temperatures from 38° to 5° centigrade provided temperature control. 

 Previous experiments by Calkins, Taylor, and Hastings had shown (for heiuidia- 

 phragms from rats) that incubation at 38° for several hours resulted in no net 

 change in potassium within the tissue, while at temperatures around 5° centigrade, 

 loss of potassium did occur. The aim of the present studies was to determine pre- 

 cisely the temperature below which potassium escaped from the striated dia- 

 phragmatic musculature of these two species. The over-all results are tabulated in 

 table I. The critical temperature for escape of potassium from the rat's diaphragm 

 is seen to lie between 15° and 17° centigrade, while for the diaphragms of hamsters 

 the critical range is significantly lower, and under the conditions of these experi- 

 ments somewhat broader than for the rat's tissue. 



These results are particularly interesting in view of the lethal lower limits for 

 body temperature as reported by Adolph." He found that for the intact rat this 

 value was approximately 15° and for the intact hamster approximately 5° centigrade. 

 Table II tabulates these values comparatively. The correlation is good and suggests 

 that the processes permitting the maintenance of a high concentration of potassium 

 within the cell may be the ones that fail as a result of hypothermia, leading to 

 death. 



Hamsters were chosen in this study for comparison with rats because hamsters 

 are hibernators and can undergo spontaneous, periodic and reversible lowering of 

 the body temperatures to levels between 2° and 5° centigrade, a degree of hypo- 

 thermia in comparison to which the present levels of clinical hypothermia seem 

 sub-tropical. 



The next experiments deal with the effects of temperature upon the behavior 

 of the rat's heart. In these experiments, the heart was removed from an etherized, 

 heparinized rat, the aorta was cannulated with a glass tube and placed in a per- 

 fusion apparatus, which was inserted in a water bath, the temperature of which 

 could be varied from 5° to 38° centigrade. By way of the aortic cannula, the coro- 

 nary system of the animal was perfused with Krebs-Ringer-bicarbonate solution 

 containing glucose. The perfusion fluid was collected as it dripped from the heart, 

 was re-oxygenated at the proper carbon dioxide tension, and recirculated at con- 

 stant pressure through the coronary system. A known volume of perfusion fluid 

 was used — usually between 25 and 50 ml. — and changes in electrolyte composition 

 of this fluid during perfusion yielded information about changes in electrolyte com- 

 position of the heart muscle. With the technique, spontaneous, regular contractions 

 of the heart began as soon as perfusion was started, and, with the temperature at 

 38°, would continue for from two to four hours. Electrocardiograms were taken 



