When during other studies it was unexpectedly discovered that addition of citrate ion to rat brain slices in vitro produced as much as a 27% increase in their rate of oxygen consumption, no previous report of a similar phenomenon could be found except that of Krebs and Johnson(1) who noted that citrate increased the respiratory rate of pigeon breast muscle in vitro. Lipsett and Crescitelli( 2) found that citrate prevented the increase in oxygen consumption obtained by adding 0.1 M KCI to rat brain slices in a dextrose substrate. Therefore the above findings on rat brain were investigated in vitro further; this paper concerns preliminary results showing some of the interrelated effects of ions and various substrates.Approach and methods. The standard technic of the Warburg method was used. Time elapsing between decapitation of rats and beginning of equilibration was 25 minutes (t 5) for both brain slices and brei. Concentrations of constituents in the flasks and the errors of the differences of the means are given in the tables. The pH at the start was 6.8-7.0 and changed about 0.4 unit during experimental runs. The lack of effect of a nonmetabolized carbohydrate, mannitol, was shown by the finding that oxygen consumption (pl per mg fresh wt/hr) of 0.0166 M dextrose alone was 1.26 while that of 0.0166 M dextrose plus 0.0416 M mannitol was 1.29.Results. In the first experiment (Table I, A) the effect of citrate at .0416 molar concentration in the presence of only one substrate, dextrose, was a considerable enhancement of 0 2 consumption of brain slices and brei (2 7 % and 5 1 %, respectively). Optimal concentration values of dextrose alone and of combinations of dextrose and citrate are shown in Table I (B and C). Similar enhancement was also shown clearly for the brains of several species, mouse, cat, rabbit, gupea pig and dog, at optimal concentrations found for the rat (Table 11). When 3 rat organs other than brain were tested, enhancement was found in heart and kidney, but not in liver (Table 11).We investigated how much increase in 0 2 consumption resulted from addition of Krebscycle intermediates with and without dextrose (Fig. 1, 2). In Krebs-Ringer phosphate medium only lactate gave a greater respiratory rate than dextrose alone, while pyruvate, oxalacetate, and ketoglutarate gave the same, and malate, fumarate, and citrate gave less (Fig. 1C). In the presence of dextrose, however, only citrate gave enhancement (Fig. 2 B) in Krebs-Ringer medium If phosphate ion concentration was varied, the substrate effects were different. When at EMORY UNIV on August 15, 2015 ebm.sagepub.com Downloaded from
