VII. The temperature dependence of steady state K exchange in presence and absence of NaCl

Ernest Page ¹

¹ From the Biophysical Laboratory, Harvard Medical School, Boston.

Dr Page's present address is the Department of Zoology, University of California at Los Angeles. His permanent address is Departments of Medicine and Physiology, University of Chicago

In quiescent cat papillary muscles J_K, the rate of exchange of cellular K with K⁴² in the steady state, has been measured in the presence and absence of NaCl over a wide range of temperatures. J_K was found to be independent of the presence of external NaCl under the steady state conditions investigated. The Arrhenius plot for K exchange was linear over a range of temperatures from 2.5 to 37.5°C in the absence of NaCl, and from 17.5 to 37.5°C in the presence of NaCl. The corresponding apparent activation energies were, respectively, 10,200 and 8,800 calories/mole. J_K in the absence of NaCl was not affected by 10^-5 M ouabain. These results are consistent with a passive distribution for the K of heart muscle cells. The observations suggest that a carrier-mediated forced exchange of K for Na does not occur during the steady state in mammalian heart muscle.

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