| Abstract: | Oxidation of U14C]lactate to 14CO2 was measured in vitro, in nonperfused anatomically defined segments of rabbit proximal tubule (S1, proximal convoluted, and S2 and S3, proximal straight tubules). The rate of lactate oxidation was similar in S2 and S3 segments, and within the range of lactate oxidation rates measured in vivo. In contrast, the oxidation rate of S1 segments was significantly lower than that of S2 or S3. In proximal straight tubules, lactate oxidation was inhibited by incubation at 0 degrees C, or by application of 1 mM ouabain. To determine if the rate of transepithelial transport affected the rate of lactate oxidation, lactate oxidation was measured in proximal straight tubules after the lumen had been opened by perfusion with Ringer's containing 10 mM polyethylene glycol. No difference in lactate oxidation rate was observed between tubules with patent lumina and nonperfused tubules. These results suggest that the various segments of the renal proximal tubule have different metabolic characteristics, and that the rate of substrate oxidation is related to the activity of the Na+, K+-ATPase. |
