The multidrug transporter MATE1 sequesters OCs within an intracellular compartment that has no influence on OC secretion in renal proximal tubules

Abstract

Secretion of organic cations (OCs) across renal proximal tubules (RPTs) involves basolateral OC transporter (OCT)2-mediated uptake from the blood followed by apical multidrug and toxin extruder (MATE)1/2-mediated efflux into the tubule filtrate. Whereas OCT2 supports electrogenic OC uniport, MATE is an OC/H(+) exchanger. As assessed by epifluorescence microscopy, cultured Chinese hamster ovary (CHO) cells that stably expressed human MATE1 accumulated 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 human OCT2-expressing cells was largely restricted to the cytoplasm. A second intracellular compartment was also evident in the multicompartmental kinetics of efflux of the prototypic OC [(3)H]1-methyl-4-phenylpyridinium (MPP) from MATE1-expressing CHO cells. Punctate accumulation of NBD-MTMA was markedly reduced by coexposure of MATE1-expressing cells with 5 μM bafilomycin (BAF), an inhibitor of V-type H(+)-ATPase, and accumulation of [(3)H]MPP and [(3)H]NBD-MTMA was reduced by >30% by coexposure with 5 μM BAF. BAF had no effect on the initial rate of MATE1-mediated uptake of NBD-MTMA, suggesting that the influence of BAF was a secondary effect involving inhibition of V-type H(+)-ATPase. The accumulation of [(3)H]MPP by isolated single nonperfused rabbit RPTs was also reduced >30% by coexposure to 5 μM BAF, suggesting that the native expression in RPTs of MATE protein within endosomes can increase steady-state OC accumulation. However, the rate of [(3)H]MPP secretion by isolated single perfused rabbit RPTs was not affected by 5 μM BAF, suggesting that vesicles loaded with OCs(+) are not likely to recycle into the apical plasma membrane at a rate sufficient to provide a parallel pathway for OC secretion.

Transport Turnover Rates for Human OCT2 and MATE1 Expressed in Chinese Hamster Ovary Cells

“…Nevertheless, virtually all knowledge of the kinetic and selectivity characteristics of MATEs comes from studies of substrate uptake. The emphasis on assessing uptake (rather than efflux) reflects the comparative ease of measuring the former compared to the latter [50,51], and although the kinetic characteristics of efflux need not be the same as those for uptake [19], it is the usual working assumption (with appropriate interpretive caveats) and the one we used here. However, a second complicating factor that MATEs present reflects the pivotal role of H + concentration on MATE activity, and methodological differences between our study and that of Yin et al [21] certainly contributed to the higher rates of transport determined in our experiments.…”

Contribution of multidrug and toxin extrusion protein 1 (MATE1) to renal secretion of trimethylamine-N-oxide (TMAO)

“…While the direction of transport by the proton-coupled cation exchanger MATE1 largely depends on the pH gradient between extra- and intracellular medium 17 , 21 , 22 , substrate affinity on the extra- and intracellular moieties of the transporter protein may be different 35 . A high affinity on the intracellular moiety along with a comparatively low affinity on the extracellular would result in higher rate of efflux, independently of the direction of the pH gradient.…”

Interaction of buspirone and its major metabolites with human organic cation transporters

“…For the uptake assay, the cells were incubated with 10 μM of DAPI in the absence or presence buspirone (0.1-500 μM) for 10 min. For DAPI efflux study, the cells were incubated with 10 μM of DAPI for 10 min and then the incubation buffer was replaced with D-PBS containing Bu at various concentrations for another 10 min as modified from previously described [25,26]. The reaction was then stop by washing with ice-cold D-PBS.…”