Lui E C, Bendayan R
Faculty of Pharmacy, University of Toronto, ON, Canada.
Can J Physiol Pharmacol. 1998 Feb;76(2):155-60.
The mechanisms by which aminoglycosides are transported across the luminal membrane of renal proximal tubular cells remain unclear. A luminal organic cation/H+ exchange as well as an adsorptive endocytosis membrane process has been proposed to be involved in gentamicin renal accumulation. The objectives of this work were to explore further the effects of intracellular and extracellular pH changes on gentamicin uptake. [3H]Gentamicin uptake by a continuous renal epithelial cell line, LLCPK1, grown as a monolayer on an impermeable surface was measured at different temperatures and pH conditions and in the presence of various inhibitors. Uptake of gentamicin was found to be carrier mediated (K(m) = 1.26 +/- 0.22 mM, Vmax = 289 +/- 27 pmol.mg-1.min-1), energy dependent (inhibited in part by sodium azide), and temperature dependent (37 degrees C > 4 degrees C). Fifteen-minute gentamicin (10 microM) uptake was inhibited by 1 mM of the organic cations cimetidine (61.0%), quinidine (73.5%), quinine (68.6%), and verapamil (61.5%). More importantly, while an outwardly directed proton gradient did not have a significant effect on gentamicin uptake, extracellular acidification (pH 6.5), which leads to a higher degree of gentamicin ionization, significantly enhanced gentamicin uptake by LLCPK1 monolayer cells. These results suggest that the luminal organic cation/H+ exchanger is not involved in gentamicin uptake by renal cultured epithelial cells. Rather, the cationic charge of gentamicin appears to be one of the primary determinants for renal luminal uptake.
氨基糖苷类药物跨肾近端小管细胞腔面膜转运的机制尚不清楚。有人提出，腔面有机阳离子/氢离子交换以及吸附性胞吞膜过程参与庆大霉素在肾脏的蓄积。本研究的目的是进一步探讨细胞内和细胞外pH值变化对庆大霉素摄取的影响。在不同温度、pH条件下以及存在各种抑制剂的情况下，测量了在不可渗透表面上以单层生长的连续肾上皮细胞系LLCPK1对[3H]庆大霉素的摄取。发现庆大霉素的摄取是载体介导的（米氏常数K(m)=1.26±0.22 mM，最大速度Vmax=289±27 pmol·mg-1·min-1），能量依赖的（部分受叠氮化钠抑制），且温度依赖的（37℃＞4℃）。1 mM的有机阳离子西咪替丁（61.0%）、奎尼丁（73.5%）、奎宁（68.6%）和维拉帕米（61.5%）可抑制15分钟的庆大霉素（10 microM）摄取。更重要的是，虽然外向质子梯度对庆大霉素摄取没有显著影响，但细胞外酸化（pH 6.5）会导致庆大霉素更高程度的离子化，从而显著增强LLCPK1单层细胞对庆大霉素的摄取。这些结果表明，腔面有机阳离子/氢离子交换体不参与肾培养上皮细胞对庆大霉素的摄取。相反，庆大霉素的阳离子电荷似乎是肾腔摄取的主要决定因素之一。
