MATE1 sequesters organic cations within an intracellular, bafilomycin‐sensitive compartment (892.39)

Abstract

OC secretion across renal proximal tubules (RPTs) involves basolateral OCT2‐mediated uptake from the blood, followed by apical MATE1/2‐mediated efflux into the tubule filtrate. Whereas OCT2 is an electrogenic OC uniporter, MATE is an OC/H exchanger. Epifluorescence microscopy of hMATE1‐expressing CHO cells revealed accumulation of the fluorescent OC, N,N,N‐trimethyl‐2‐[methyl(7‐nitrobenzo[c][l,2,5]oxadiazol‐4‐yl)amino]ethanaminium (NBD‐MTMA) in the cytoplasm and in a smaller, punctate compartment; accumulation in OCT2 expressing cells was restricted to the cytoplasm. A second intracellular compartment was also evident in the multicompartmental kinetics of NBD‐MTMA efflux from MATE1‐CHO cells. Punctate accumulation (20 min) was markedly reduced by coexposure of MATE1‐CHO cells with 1 μM bafilomycin (BAF) and eliminated with 10 μM BAF. BAF had no effect on the initial rate of MATE1‐mediated uptake of NBD‐MTMA (10‐120 sec) suggesting that its effect involved collapse of endosomal pH gradients via inhibition of the V‐type H‐ATPase. The 15 min accumulation of the prototypic OC, [³H]TEA by isolated single non‐perfused rabbit RPTs was also reduced 40% by coexposure to 1 μM BAF. Thus, the native expression in RPTs of MATE protein within endosomes can increase steady‐state OC accumulation. Normal rates of apical endosome turnover may provide a significant parallel pathway for apical OC effluxGrant Funding Source: NIH grant 5R01DK080801