324 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



48. Bernstein, J.: Elektrobiologie; die Lehre von den electrischen Vorgangen im Organismus 



auf moderner Grundlage dargestellt, F. Vieweg & Sohn, Braunschweig, 1912. 



49. Daly, I. de Burgh, and Clark, A. J. : The action of ions upon the frog's heart, J. Physiol. 54: 



m, 1921. 



50. Pinkston, J. O., Kao, F. F., and Brooks, C. McC. : Studies on the excitability of the heart as 



tested by chronically implanted electrodes and the effects of temperature thereon, Abstr. 

 19th Internat. Physiol. Congress, Montreal, 1953, p. 681. 



51. Hoffman, B. F. : Unpublished observations. 



52. Lepeschkin, E. : Modern electrocardiography, Vol. 1, Williams and Wilkins, Baltimore, 1951. 



53. Hamilton, J. B., Dresbach, M., and Hamilton, R. S. : Cardiac changes during progressive 



hypothermia, Amer. J. Physiol. 118: 71, 1937. 



54. Hodgkin, A. L., and Katz, B. : The effect of temperature on the electrical activity of the giant 



axon of the squid, J. Physiol. 109: 240, 1949. 



55. Wiggers, C. J. : Physiology in health and disease, Lea & Febiger, Philadelphia, 1944. 



56. Hoff, H. E. : Fulton's Textbook of Physiology, Ed. 16, Saunders, Philadelphia. 



57. Coraboeuf, E., and Boistel, J. : L'action des taux eleves de gaz carbonique sur le tissu 



cardiaque etudiee a I'aide de microelectrodes, C. R. Soc. Biol. 147 : 654, 1953. 



58. Huxley, A. F., and Stampfli, R. : Effect of potassium and sodium on resting and action 



potentials of single myelinated nerve fibers, J. Physiol. 112: 496, 1951. 



59. Ling, G., and Gerard, R. W. : External potassium and the membrane potential of muscle 



fibers, Nature 165: 113, 1950. 



60. Weidmann, S. : Personal communication. 



61. Jenerick, H. P., and Gerard, R. W. : Membrane potential and threshold of single muscle 



fibers, J. Cell. Comp. Physiol. 42: 79, 1953. 



62. Hoffman, B. F., and Suckling, E. E. : Microelectrode studies of repolarization in the dog 



ventricle, Abstr. 19th Internat. Physiol. Congress, Montreal, 1953. 



63. Ware, F., Jr., Bennet, A. L., and Mclntyre, A. R. : Cellular potentials in frog hearts. Fed. 



Proc. i^; 158, 1955. 



DISCUSSION 



Dr. George E. Burch: I would like to ask two questions. 



When one speaks of membrane permeability, is that strictly meant, or is it possi- 

 ble that there may be some alteration in molecular orientation or configuration 

 which might produce polarization states, ionic states, for example, within the sur- 

 face of the cell or some part of the cell? 



Also, were sodium chloride, pH, and bicarbonate measured? A paper published 

 in Circulation Research reported that in dogs changes attributed to potassium were 

 also found to be produced by changes of sodium pH, bicarbonate or some other ion. 

 Because of the complex relationship of some of these ions, one could get confusing 

 impressions as to which ion was actually at work. 



Dr. Hoffman: I can try to answer the second question very briefly: In terms of 

 induced changes in extracellular cations, in all cases the simultaneous concentrations 

 of sodium chloride, magnesium, etc. have been controlled. With very marked 

 changes, let's say for example when potassium was increased by a multiple of ten, 

 the total ionic strength of the Tyrode solution was maintained by decreasing sodium. 

 In most instances we have maintained adequate control of the extracellular ionic 

 concentration. In most of this work H ion and bicarbonate are reasonably constant. 

 Even with changes in temperature we can keep pH well controlled. 



With regard to the first question, as far as changes in niem1)rane permeability 

 are concerned, in speaking of the changes wliich occur diu-ing a normal action po- 

 tential, the major evidence for a permeability change is probal)!)- the decrease and 



