Influence of substrate structure on turnover of the organic cation/H+ exchanger of the renal luminal membrane.
Influence of substrate structure on turnover of the organic cation/H+ exchanger of the renal luminal membrane.
复制标题
底物结构对肾腔膜有机阳离子/H交换剂周转的影响。
DOI：
10.1007/s004240050658
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Wunz,TM
中科院分区：
文献类型：
--
作者：
Wright,SH;Wunz,TM
我们研究了有机阳离子（OC）结构对兔肾刷状缘膜囊泡（BBMV）中OC/H+交换器转换速率的影响。[14 C]四乙基铵（[14 C]TEA）从BBMV流出的速率，在测试试剂的向内指向的化学梯度的存在下测量，提供了OC/H+（OC）交换剂活性的间接测量。[14 C]TEA从BBMV流出的反式刺激是增加未标记TEA和四甲基铵（TMA）囊外浓度的饱和函数，这些化合物与OC/H+（OC）交换剂相互作用的表观米氏常数（Kt）分别为25 µM和1 mM。研究了一系列n-四烷基铵化合物的饱和囊外浓度对[14 C]TEA流出的影响。而短链化合物TMA和TEA显着刺激[14 C]TEA外排（分别为830%和690%），长链化合物四丙基铵和四丁基铵的有效性较低，增加外排分别只有40%和120%。当交换器用四戊基铵饱和时，[14 C]TEA的介导流出减少。增加烷基链长度也与这些化合物对OC/H+（OC）交换剂转运[14 C]TEA的抑制作用的增加（如通过表观抑制常数Ki或IC 50值测量的）相关;即，IC_（50）降低与OC/H ~+（OC）交换器周转率降低相关。对于更广泛的一组不同分子结构的测试试剂，包括一系列n-四烷基铵和磷化合物以及OC、胆碱、N1-甲基烟酰胺、1-甲基-4-苯基吡啶鎓和阿米洛利，观察到相同的相关性。由于高亲和力的OC/H+（OC）交换器的基板与增加基板的疏水性，我们得出结论，疏水OC与肾OC/H+（OC）交换器的相互作用的结果在形成的基板交换器复合物，具有相对较低的周转率。
We examined the influence of organic cation (OC) structure on the rate of turnover of the OC/H+exchanger in rabbit renal brush-border membrane vesicles (BBMV). The rate of efflux of [14C]tetraethylammonium ([14C]TEA) from BBMV, measured in the presence of an inwardly directed chemical gradient for test agent, provided an indirect measure of activity of the OC/H+(OC) exchanger. Thetrans-stimulation of [14C]TEA efflux from BBMV was a saturable function of increasing extravesicular concentration of both unlabeled TEA and tetramethylammonium (TMA), with an apparent Michaelis constant (Kt) for the interaction of these compounds with the OC/H+(OC) exchanger of 25 µM and 1 mM, respectively. The effect on [14C]TEA efflux of saturating extravesicular concentrations of a series ofn-tetraalkylammonium compounds was examined. Whereas the short-chain compounds TMA and TEA markedly stimulated [14C]TEA efflux (by 830% and 690%, respectively), the long-chain compounds tetrapropylammonium and tetrabutylammonium were less effective, increasing efflux by only 40% and 120%, respectively. When the exchanger was saturated with tetrapentylammonium, mediated efflux of [14C]TEA was reduced. Increasing alkyl chain length was also correlated with an increase in the inhibitory effect (as measured by the apparent inhibition constant,Ki, or the IC50value) that these compounds had against transport of [14C]TEA by the OC/H+(OC) exchanger; i.e., there was a correlation between decreasing IC50and decreasing turnover of the OC/H+(OC) exchanger. This same correlation was observed for a broader set of test agents of diverse molecular structure, including a series ofn-tetraalkylammonium and -phosphonium compounds and the OCs, choline,N1-methyl nicotinamide, 1-methyl-4-phenylpyridinium, and amiloride. Because high affinity of substrates for the OC/H+(OC) exchanger is correlated with increasing substrate hydrophobicity, we conclude that the interaction of hydrophobic OCs with the renal OC/H+(OC) exchanger results in the formation of a substrate-exchanger complex that has a comparatively low rate of turnover.