Werner D, Martinez F, Roch-Ramel F
Institut de Pharmacologie de l'Université, Lausanne, Switzerland.
J Pharmacol Exp Ther. 1990 Feb;252(2):792-9.
The transport of urate and p-aminohippurate (PAH) across the pig renal brush border membrane was investigated using membrane vesicles. Compared to a pH equilibrium condition (pHin = 7.4; pHout = 7.4), an outwardly directed OH- gradient (pHin = 7.4; pHout = 5.8) stimulated markedly both lactate and pyrazinoate uptake with overshoots exceeding 2 times that of the steady state. In contrast, neither OH-/urate nor OH-/PAH exchange could be demonstrated. An outwardly directed Cl- gradient (Cl-in = 100 mM; Cl-out = 16.7 mM) increased 2.6-fold 15-sec PAH uptake compared to Cl- equilibrium (Cl-in = Cl-out = 100 mM) but this stimulation was due solely to an effect of membrane potential. Creation of an electropositive intravesicular space, by imposing an inwardly directed K+ gradient (K+in = 0 mM; K+out = 100 mM) in the presence of valinomycin, was very effective to drive uphill PAH and urate accumulation compared to the control condition (no valinomycin). Four-second potential-stimulated PAH uptake was saturable (Km, 0.8 mM; Vmax, 1.7 nmol/mg of protein x 4 sec). Different organic anions cis-inhibited both 4-sec potential-stimulated PAH and urate uptakes in a similar fashion. PAH and urate, moreover, decreased each other's accumulation. In countertransport experiments, PAH and urate uptakes were not significantly stimulated by trans-unlabeled substrate. These results are consistent with the presence, in the pig renal brush border membrane, of a mediated secretory pathway common for urate and PAH, which could be facilitated by the potential difference existing in vivo across the luminal membrane of the proximal tubule.
利用膜囊泡研究了尿酸盐和对氨基马尿酸（PAH）在猪肾刷状缘膜上的转运。与pH平衡条件（pHin = 7.4；pHout = 7.4）相比，外向性OH-梯度（pHin = 7.4；pHout = 5.8）显著刺激了乳酸盐和吡嗪酸盐的摄取，超射超过稳态摄取的2倍。相反，未证实存在OH-/尿酸盐或OH-/PAH交换。与Cl-平衡（Cl-in = Cl-out = 100 mM）相比，外向性Cl-梯度（Cl-in = 100 mM；Cl-out = 16.7 mM）使15秒PAH摄取增加了2.6倍，但这种刺激完全是由于膜电位的作用。在缬氨霉素存在的情况下，通过施加内向性K+梯度（K+in = 0 mM；K+out = 100 mM）来创建正电的囊泡内空间，与对照条件（无缬氨霉素）相比，对驱动PAH和尿酸盐的上坡积累非常有效。4秒的电位刺激PAH摄取是可饱和的（Km，0.8 mM；Vmax，1.7 nmol/mg蛋白质×4秒）。不同的有机阴离子以类似的方式顺式抑制4秒电位刺激的PAH和尿酸盐摄取。此外，PAH和尿酸盐会相互降低对方的积累。在反向转运实验中，PAH和尿酸盐的摄取未受到反式未标记底物的显著刺激。这些结果与猪肾刷状缘膜中存在尿酸盐和PAH共同的介导分泌途径一致，该途径可能因近端小管腔膜在体内存在的电位差而得到促进。
