Leyssac P P, Frederiksen O, Holstein-Rathlou N H, Alfrey A C, Christensen P
Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
Am J Physiol. 1994 Jul;267(1 Pt 2):F86-93. doi: 10.1152/ajprenal.1994.267.1.F86.
We tested the hypothesis that proximal tubular Li+ reabsorption is due to passive transport. Clearances of [14C]inulin (CIn) and Li+ (CLi), proximal transepithelial electrical potential difference (PD), and tubular fluid-to-plasma Li+ concentration ratios [(TF/P)Li] were measured in anesthetized rats before and after induction of osmotic mannitol diuresis. Late proximal (TF/P)Li was measured after acute intravenous LiCl administration and after addition of LiCl to the diet for 2 days. Glomerular filtration rate (CIn) decreased, whereas CNa and CLi increased during osmotic diuresis. Control early proximal PD was -0.6 mV (lumen negative); late proximal PD (PDLP) was 1.1 mV (lumen positive). PDLP decreased by 1.5 mV to -0.4 mV (lumen negative) after mannitol infusion. Late proximal (TF/P)Li was 1.01 after oral Li+, 1.16 after intravenous Li+ (P < 0.01), and 1.00 during osmotic diuresis. It is concluded that proximal Li+ transfer is distinct from that of Na+, closely parallels proximal water transfer, and involves an active transport mechanism independent of the PD. The data suggest that acute elevation of plasma Li+ concentration may activate a delayed Li+ transport pathway in the proximal convoluted tubule.
我们检验了近端肾小管Li⁺重吸收是由于被动转运这一假说。在麻醉大鼠中，于诱导渗透性甘露醇利尿前后，测量了[¹⁴C]菊粉清除率（CIn）、Li⁺清除率（CLi）、近端跨上皮电位差（PD）以及肾小管液与血浆Li⁺浓度比[（TF/P）Li]。在急性静脉注射LiCl后以及在饮食中添加LiCl 2天后，测量了近端肾小管后期的（TF/P）Li。渗透性利尿期间，肾小球滤过率（CIn）降低，而CNa和CLi升高。对照时近端肾小管早期PD为-0.6 mV（管腔为负）；近端肾小管后期PD（PDLP）为1.1 mV（管腔为正）。输注甘露醇后，PDLP降低1.5 mV至-0.4 mV（管腔为负）。口服Li⁺后近端肾小管后期（TF/P）Li为1.01，静脉注射Li⁺后为1.16（P<0.01），渗透性利尿期间为1.00。结论是近端Li⁺转运不同于Na⁺转运，与近端水转运密切平行，且涉及一种独立于PD的主动转运机制。数据表明，血浆Li⁺浓度的急性升高可能激活近端曲小管中一种延迟的Li⁺转运途径。
