Activity coefficients of intracellular Na+ and K+ during development of frog oocytes |
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Authors: | Lawrence G. Palmer Theodore J. Century Mortimer M. Civan |
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Affiliation: | (1) Departments of Physiology and Medicine, University of Pennsylvania School of Medicine, 19174 Philadelphia, Pennsylvania;(2) Present address: Cardiovascular Research Institute, University of California School of Medicine, 94143 San Francisco, California;(3) Department of Biochemistry and Biophysics, University of California School of Medicine, 94143 San Francisco, California |
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Abstract: | Summary The chemical activities, (a), of Na+ and K+ were determined in large mature and in small immature frog oocytes, using open-tipped micropipettes and ionselective microelectrodes. The average chemical concentrations,c, of Na+ and K+ were determined by spectrophotometry and by electron probe X-ray microanalysis. The apparent activity coefficient ( app) was calculated for each ion as the ratio,a/c.With development, (aNa/aK) decreased four to fivefold and (cNa/cK) increased six to sevenfold. In the large mature oocytes, Naapp was measured to be 0.08±0.02 and Kapp lay within the range 1.15±0.03 to 1.29±0.04, constituting the smallest value for Na+ and largest value for K+, respectively, thus far reported. This intracellular value of Kapp was substantially greater than the activity coefficient of K+ in the external medium (0.76). The data suggest that the inequality of Naapp and Kapp in this and probably other cells reflects the development of subcellular compartmentalization of ions. Possible intracellular sites of ionic compartmentalization are considered. |
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