Relationship between sodium transport and oxygen consumption in the isolated perfused rat kidney

The purpose of the present experiments was to determine the relationship between Na+ transport and O2 consumption of the perfused rat kidney in vitro. The delta Na/delta O2 ratio was calculated from the change in Na+ transport and the change in O2 consumption. Na+ transport was varied by lowering perfusion pressure or adding ouabain. Previous investigators have calculated the delta Na/delta O2 ratio for the kidney in vivo by combining all data points in each group of experiments. Using this approach, the delta Na/delta O2 ratio of the perfused kidneys was 66.3 +/- 22.0 for the low pressure perfusion experiments and 29.1 +/- 3.1 for the ouabain experiments. These values are at least as great as those reported for the kidney in vivo. The delta Na/delta O2 ratios were also calculated by determining the regression line for each individual kidney, and then obtaining the mean of these regressions. Using this approach, the delta Na/delta O2 ratio for the low pressure perfusion experiments was 37.0 +/- 7.4 and the delta Na/delta O2 ratio for the ouabain experiments was 20.3 +/- 1.7. These values are significantly lower than the ratios obtained by combining all data points. The ratio of absolute Na+ transport to absolute O2 consumption (Na/O2 ratio) was 13.1 +/- 0.5 for control experiments. This value is considerably less than that obtained for the kidney in vivo. The extrapolated rate of O2 consumption in the absence of sodium transport (i.e. nontransport metabolism) was 40-63% of the control rates of oxygen consumption; this is a much higher fraction of 'nontransport' metabolism than in the kidney in vivo. It is concluded that the metabolic efficiency of the perfused kidney is considerably less than that of the kidney in vivo. Furthermore, the present results cast doubt on the usefulness of the delta Na/delta O2 ratio as in index of efficiency of Na+ transport by the kidney.