On the coupling of respiration to cation transport in slices of rat liver

Abstract

1. 1. Rat-liver slices utilizing endogenous substrate respired at a rate of 9.2 μl O 2 per mg fat-free dry wt. per h, in a medium containing 5 mM K + and 161 mM Na +. Inhibition of the active transport of Na + and K + by ouabain, reduced the rate of respiration of these slices by 2.4 μl O 2 per mg per h (26% inhibition). 2. 2. In a medium containing 75 mM K + and 91 mM Na +, the control rate of respiration was 10.1 μl O 2 per mg fat-free dry wt. per h; ouabain lowered this by only 0.8 μl per mg per h (8% inhibition). It is suggested that the latter portion of the total O 2 uptake is coupled to the energy requirements of ion transport (‘transport-coupled respiration’). The additional inhibition caused by ouabain in the 5 mM K + medium appears to be due to changes in the oxidative metabolism resulting from the altered cation composition of the intracellular environment (‘cation-sensitive respiration’). 3. 3. Malonate and ethanol, at concentrations which are known to inhibit citric acid cycle activity, have little effect on ion transport. 4. 4. In the presence of ethanol or malonate, inhibition of ion transport (by ouabain, or K +-free medium) inhibits respiration only by an amount similar to the transport-coupled respiration (0.65–1.16 μl per mg per h). The cation-sensitive portion of the respiration appears to be due to the provision of reducing equivalents by the citric acid cycle. 5. 5. Approximate calculations are made of the amount of energy made available by the transport-coupled respiration, and this is compared to an estimate of the minimal energy requirement of the Na + transport.