Brand P H, Stansbury R S
Am J Physiol. 1981 May;240(5):F388-94. doi: 10.1152/ajprenal.1981.240.5.F388.
We examined the effects of experimental conditions on unidirectional lactate fluxes in isolated perfused Thamnophis proximal tubule. Fluxes were determined by adding L(+)-[U-14C]lactate to perfusate or bath as appropriate (lactate concentration = 1 mM). The lumen-to-bath lactate flux (Jlb lact) was not affected by the manipulations required to exchange perfusate or bath or by substitution of phosphate for bicarbonate buffer. During measurement of Jlb lact, lactate was ordinarily added to the perfusate only. However, addition of 1 mM lactate to the bath had no effect on Jlb lact, indicating no role for exchange diffusion in renal lactate absorption. In contrast, substitution of tetramethylammonium (TMA+) or choline for Na+ decreased Jlb lact by about 75%. The bath-to-lumen flux (Jbl lact) was also decreased by TMA+ substitution for Na+, although by only about 25%. From these and previous results we suggest that in Thamnophis proximal tubule, lactate is absorbed by an active Na+-dependent transport process that probably derives its energy from the lumen-to-cell electrochemical gradient for Na+.
我们研究了实验条件对分离灌流的束带蛇近端小管中乳酸单向通量的影响。通过将L(+)-[U-14C]乳酸适当添加到灌流液或浴液中（乳酸浓度 = 1 mM）来测定通量。管腔到浴液的乳酸通量（Jlb lact）不受更换灌流液或浴液所需操作的影响，也不受用磷酸盐替代碳酸氢盐缓冲液的影响。在测量Jlb lact期间，通常仅将乳酸添加到灌流液中。然而，向浴液中添加1 mM乳酸对Jlb lact没有影响，表明交换扩散在肾脏乳酸吸收中不起作用。相比之下，用四甲基铵（TMA+）或胆碱替代Na+可使Jlb lact降低约75%。用TMA+替代Na+也会使浴液到管腔的通量（Jbl lact）降低，尽管仅降低约25%。根据这些以及之前的结果，我们认为在束带蛇近端小管中，乳酸是通过一种依赖Na+的主动转运过程被吸收的，该过程可能从管腔到细胞的Na+电化学梯度获取能量。
