Involvement of OCTN1 (SLC22A4) in pH-Dependent Transport of Organic Cations

Abstract

OCTN1 (SLC22A4) transports cationic compounds such as tetraethylammonium in a pH-sensitive and sodium-independent manner in cultured cells, and is expressed in wide variety of tissues, including kidney, muscle, placenta, heart, and others. This study focused on the clarification of its subcellular distribution in kidney and on its driving force to throw light on the pharmacological and physiological roles of OCTN1. Uptake of [14C]tetraethylammonium by membrane vesicles prepared from HEK293 cells stably transfected with human OCTN1 cDNA was osmolarity-sensitive, and the Km of tetraethylammonium was 1.28 mM at intravesicular and extravesicular pH values of 6.0 and 7.4, respectively. Tetraethylammonium uptake was pH-dependent, and overshoot uptake was observed in the presence of an outwardly directed proton gradient. A protonophore and membrane potential affected the overshoot uptake. Furthermore, preloading tetraethylammonium in the vesicles significantly increased the rate of uptake of [14C]tetraethylammonium. In mouse kidney, OCTN1 was expressed predominantly at the apical membrane of cortical proximal tubular epithelial cells. It was concluded that OCTN1 is involved in renal excretion of organic cations across the apical membrane in a pH-dependent, membrane potential-sensitive manner and is affected significantly by the organic cations on the trans side, showing counter transport activity.

Gene Knockout and Metabolome Analysis of Carnitine/Organic Cation Transporter OCTN1

“…This may support the hypothesis that the liver plays a first-pass elimination organ in wild-type mice, but not in octn1 -/-mice, although this hypothesis should be verified by the further analyses. The higher urinary excretion of ergothioneine in octn1 -/-mice would be due to reabsorption of ergothioneine by OCTN1 if we consider that OCTN1 is localized on brush-border membranes of proximal tubules (22), can transport ergothioneine ( Figure 2) and is involved in influx of ergothioneine in renal brush-border membrane vesicles (Supplemental Figure 3). Both ergothioneine level (Table I) and tissue distribution of (Fig.…”

“…Because quite limited information is available on details in biodistribution kinetics of ergothioneine in the body, we next examined the absorption and disposition of Figure 3). This suggests that ergothioneine is reabsorbed by OCTN1 in wild-type mice, but not in octn1 -/-mice if we consider that OCTN1 is localized on brush-border membranes of proximal tubules (22). The octn1 -/-mice showed a lower tolerance to intestinal oxidative stress.…”

Functional Expression of Carnitine/Organic Cation Transporter OCTN1/SLC22A4 in Mouse Small Intestine and Liver

“…It is ubiquitously distributed, being particularly highly expressed in the kidney, and is localized on the apical membrane of renal proximal tubular epithelial cells (Tamai et al, 2000(Tamai et al, , 2004. OCTN1 transports several cationic compounds, including tetraethylammonium (TEA), pyrilamine, quinidine, verapamil, donepezil, betonicine, ergothioneine (ERGO), and stachydrine (Yabuuchi et al, 1999;Grü ndemann et al, 2005).…”

Potential pharmacokinetic role of organic cation transporters in modulating the transcorneal penetration of its substrates administered topically

“…34 Hence the objective of this study was to investigate the functional importance of OCT-mediated carrier system on in vivo corneal penetration using appropriate substrates and blockers as pharmacological tools. To achieve this, TEA 20,23,[35][36][37] and metformin 23,[38][39][40][41][42] were used as OCT substrates. Quinidine 23,36,[43][44][45] and atropine 9,23 were used as OCT blockers.…”

“…Compounddependent parameters such as declustering potential, entrance potential, collision energy and cell exit potential were set at 41,8,35, and 5 V, respectively. Nitrogen gas flow for collision-induced dissociation and dwell time were kept at 4 (arbitrary value) and 100 ms, respectively.…”