Figure 2.
Detection of potential endogenous Oat3 substrates. (A) GC/MS analysis was performed to determine the levels of approximately 30 of the most abundant endogenous OA in plasma and urine. For each compound, the ratio of the concentration in urine (normalized to creatinine) to the concentration in plasma was calculated, representing a measure of the efficiency of renal excretion. Urine/plasma ratios of these compounds were largely unaffected in Oat3−/− mice (left). In comparison, several compounds manifested markedly lower urine/plasma ratios (i.e., lower apparent renal excretion) in Oat1−/− compared with WT mice, indicating the involvement of Oat1 in their tubular secretion (data taken from reference28). Notably, the urine/plasma ratio for α-ketoglutarate, which serves as a counterion for OA uptake, was greater in Oat1−/− compared with WT mice but unaffected in Oat3−/− mice. Data are means ± SEM (n = 4 per genotype). (B) A global mass-spectrometric (metabolomic) analysis was performed to compare the plasma and urine metabolite composition of Oat3−/− and WT mice. Data presented are the mean intensity values for the 100 compounds each in plasma and urine that were the most significantly different in intensity between Oat3−/− and WT mice. The majority (81%) of the significantly varying compounds in plasma were increased in Oat3−/− relative to WT, whereas the majority (64%) of those in urine were decreased in Oat3−/− relative to WT, consistent in each case with diminished renal excretion of the corresponding compounds.