Brand P H, Stansbury R S
Am J Physiol. 1980 Mar;238(3):F218-28. doi: 10.1152/ajprenal.1980.238.3.F218.
Proximal tubules from the kidney of Thamnophis (garter snake) were perfused in vitro and unidirectional fluxes of lactate measured using L(+)-[U-14C]lactate, (lactate concentration, 1 mM). The lumen-to-bath (absorptive) flux (Jlb lact) significantly exceeded the bath-to-lumen flux (backflux) (Jbl lact) in each of 12 tubules (seven distal proximal and five proximal proximal). The flux ratio (Jlb lact/Jbl lact) was approximately 3.00. At flow rates of 13-16 nl/min and lactate concentration of 1 mM the net flux was about 1.60 pmol . min-1 . mm-1 in both proximal proximal and distal proximal segments. Both fluxes were decreased by perfusion at 5 degrees C. To determin e the contribution of metabolism of lactate to its absorption, Jlb lact was measured at 25 degrees C in 10 distal proximal tubules during perfusion with [14C]lactate, lactate concentration, 1 mM, and with [methoxy-3H]inulin. In these experiments, the amount of 14C found in the bath was 93% of the amount of 14C absorbed from the lumen. Chromatography showed that all of the 14C found in the bath was [14C]lactate. These data establish that in Thamnophis proximal tubule lactate absorption occurs against an electro chemical gradient by transport of the intact lactate molecule without significant metabolism.
对束带蛇肾脏的近端小管进行体外灌注，使用L(+)-[U-¹⁴C]乳酸（乳酸浓度为1 mM）测量乳酸的单向通量。在12个小管（7个远侧近端小管和5个近侧近端小管）中，管腔到浴液（吸收性）通量（Jlb lact）显著超过浴液到管腔通量（反向通量）（Jbl lact）。通量比（Jlb lact/Jbl lact）约为3.00。在流速为13 - 16 nl/min且乳酸浓度为1 mM时，近侧近端和远侧近端段的净通量约为1.60 pmol·min⁻¹·mm⁻¹。在5℃灌注时，两种通量均降低。为了确定乳酸代谢对其吸收的贡献，在25℃下，用[¹⁴C]乳酸（乳酸浓度为1 mM）和[甲氧基-³H]菊粉灌注10个远侧近端小管时测量Jlb lact。在这些实验中，浴液中发现的¹⁴C量是从管腔吸收的¹⁴C量的93%。色谱分析表明，浴液中发现的所有¹⁴C都是[¹⁴C]乳酸。这些数据表明，在束带蛇近端小管中，乳酸的吸收是通过完整乳酸分子的转运逆电化学梯度进行的，没有明显的代谢。
