Effects of potassium, ouabain and valinomycin on the efflux of 24Na+ and pyridine nucleotides of rat-liver slices

Abstract

1. The efflux of 24Na+ from rat-liver slices incubated in a K+-free medium was stimulated by 40% when 6.4 mM K+ was added to the medium. 2. The K+-dependent portion of the efflux was completely inhibited by ouabain; ouabain also slightly inhibited the efflux of 24Na+ into K+-free medium. 3. In one-third of the experiments, treatment with K+ caused an oxidation of pyridine nucleotides which was reversed by subsequent removal of K+ or treatment with ouabain; this was consistent with the transition of the slice mitochondria towards a more active metabolic state upon stimulation of ion transport. 4. In the remaining experiments, K+ induced a reduction of pyramide nucleotides which was little affected by removal of K+ or ouabain treatment; comparison with the effect of Amytal suggests that the pyridine nucleotide so reduced was exclusively NAD+ of the respiratory chain. The reduction process appears to be largely independent of the effect of K+ on ion transport. 5. Valinomycin tended to inhibit 24Na+ efflux slightly in the presence of K+. It caused a small reduction of the pyridine nucleotides.