Induced and spontaneous movements of potassium ions into mitochondria

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Abstract
Net movements of K+ into metabolizing liver mitochondria before and after the addition of valinomycin have been measured by using selective glass electrodes. The advantage of using an automatic titrator to hold the K+ concentration constant is demonstrated. According to the energy source provided the induced movement after the addition of valinomycin can be either in or out. Uptakes and rates of movement are higher in media containing acetate (20 mM) than in media containing chloride (20mM). In each mixture comparisons were made at three pH values; at pH 6.36 the induced rates are less than at pH 7.0 or 7.8 but the final uptakes attained are increased. The rate of uptake is increased by inorganic phosphate. The presence of Mg2+ slightly decreases the induced uptake and rate of movement; Ca2+ can cause the induced movement of K+ to be outward. The rate of induced K+ movement is related to the rate of extra O2 consumption but with different factors in acetate (24 K+ ions/O2 molecule) and chloride media (10 K+ ions/O2 molecule). The amount of K+ gained is proportional to the loss of fluorescence of the suspension. When K+ moves there is a contrary movement of H+ but the ratio depends on the conditions. At pH 6.36 in chloride media the K+/H+ ratio exceeded 10:1 and in no case did it fall to unity. When K+ is taken up there is a proportional diminution of light-scattering; it is inferred that swelling takes place along with K+ accumulation. It is shown by the use of tracer 42K+ that turnover of the ion in mitochondria is increased by valinomycin. It is concluded that valinomycin both increases the permeability to K+ and also, given an adequate energy supply, stimulates the K+-accumulating mechanism.

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