DECREASED RESISTANCE TO TUMOR CELLS 377have been obtained with mitochondria from liver.As proposed in the drawing of Fig. 3, an increased rate of influx of labeled anions with acidification, or of cations with alkalinization, might be anticipated on the basis of change in permeability due to change in surface charge. Alteration in permeability would affect bidirectional flux and would serve to explain the changes with potassium, at least in the range between pH 7.2 and 8.5. On the other hand, if a net increase in content is involved, such as is the case with chloride below pH 7, permeability would be critical only if it were the rate limiting step. One may presume that cell membranes do have end groups with dissociation constants in the physiological range, and hence that the reaction pattern of Fig. 3 does have some importance generally. There is, however, little to go on with respect to quantitative significance. The results obtained with imidazole emphasize a synergistic effect due to change in charge of the free ions in solution.Summary. Change in the pH of the incu-bation medium has been shown to have opposite effects upon influx rates of cations and of anions into mitochondria1 substance. Alkalinization was associated with increase in influx of Na+ and K+; and conversely, acidification resulted in more rapid influx of B r and C1-. Increased sensitivity to pH change was observed in the presence of the buffer ion imidazole. At pH. 7 imidazole carries a positive charge and inhibition to influx of Na+ was observed. The inhibition was absent at pH 8.5 with conversion to the uncharged free base.

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