1,1?-Diethyl-2,2?-cyanine (decynium22) potently inhibits the renal transport of organic cations

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Abstract
Summary The excretion of cationic compounds by renal proximal tubule cells involves at least two distinct transporters: the basolateral type which transports organic cations from the plasma into the proximal tubule cell, and the apical type which secretes the organic cations into the lumen of the tubule. However, potent inhibitors were known for neither type of transporter. Here we introduce a compound, decynium22, that potently, competitively, and selectively inhibits the apical type of the renal organic cation transporter. The transport of the prototypical organic cation 14C-tetraethylammonium through the apical plasma membrane of clonal proximal tubule cells (LLC-PK1) was used as experimental system. Initial rates of 14C-tetraethylammonium transport into LLC-PK1 cells were saturable, the Km and Vmax being 27 μmol/l and 200 pmol/(mg protein · min), respectively. Decynium 22 competitively and potently inhibited 14C-tetraethylammonium transport (Ki = 5.6 nmol/l). Moreover, the effect of decynium22 on basolateral to apical directed transepithelial transport of 14C-tetraethylammonium through a confluent monolayer of LLC-PK1 cells was determined. Decynium22 (30 nmol/l) applied to the apical medium, reduced transepithelial transport by 76% and increased intracellular accumulation of 14C-tetraethylammonium 1.5-fold. In contrast, application of 30 nmol/l decynium22 to the basolateral medium failed to affect transepithelial transport and intracellular accumulation of 14C-tetraethylammonium. Decynium22 is the most potent inhibitor of the renal transport of organic cations known so far. With decynium22 it is now possible to distinguish precisely between a decynium22-sensitive apical type and a decynium22-resistant basolateral type of renal organic cation transporter in renal proximal tubule cells.