Transport of cimetidine by flounder and human renal organic anion transporter 1

Abstract

Burckhardt. Transport of cimetidine by flounder and human renal organic anion transporter 1. Am J Physiol Renal Physiol 284: F503-F509, 2003. First published November 12, 2002 10.1152/ajprenal.00290.2002The H 2-receptor antagonist cimetidine is efficiently excreted by the kidneys. In vivo studies indicated an interaction of cimetidine not only with transporters for basolateral uptake of organic cations but also with those involved in excretion of organic anions. We therefore tested cimetidine as a possible substrate of the organic anion transporters cloned from winter flounder (fROAT) and from human kidney (hOAT1). Uptake of [ 3 H]cimetidine into fROAT-expressing Xenopus laevis oocytes exceeded uptake into control oocytes. At Ϫ60-mV clamp potential, 1 mM cimetidine induced an inward current, which was smaller than that elicited by 0.1 mM PAH. Cimetidine concentrations exceeding 0.1 mM decreased PAH-induced inward currents, indicating interaction with the same transporter. At pH 6.6, no current was seen with 0.1 mM cimetidine, whereas at pH 8.6 a current was readily detectable, suggesting preferential translocation of uncharged cimetidine by fROAT. Oocytes expressing hOAT1 also showed [ 3 H]cimetidine uptake. These data reveal cimetidine as a substrate for fROAT/hOAT1 and suggest that organic anion transporters contribute to cimetidine excretion in proximal tubules.winter flounder renal organic anion transporter; organic anion transport; organic cation transport; kidney AS A SPECIFIC ANTAGONIST OF histamine H 2 receptors, cimetidine acts on gastric parietal cells to inhibit HCl secretion stimulated by histamine, pentagastrin, and acetylcholine. Between 50 and 80% of the dose administered intravenously was recovered in urine as unchanged cimetidine, and elimination half-life was ϳ2 h in healthy volunteers with normal kidney and hepatic function (24). The mean steady-state plasma concentration on a standard 1,000-mg daily dose was 1 g/ml (range 0.64-1.64 g/ml). A renal clearance of 600 ml/ min (24), exceeding the glomerular filtration rate by approximately fivefold, indicated an efficient tubular secretion of cimetidine. Therefore, cimetidine must interact with renal transporters, most probably with those located in the proximal tubules.Because at physiological pH part of the cimetidine is positively charged, the organic cation transport systems of the proximal tubule cell are expected to be involved in cimetidine secretion. The two-step model of transcellular organic cation secretion consists of electrogenic uptake at the basolateral side, moving organic cations down their electrochemical gradient from blood into proximal tubular cells, and organic cation/proton exchange mediating uphill exit into the lumen. The cloned organic cation transporters, OCT1, OCT2, and OCT3, are electrogenic and likely contribute to organic cation uptake across the basolateral membrane (for reviews, see Refs. 6 and 18). In accordance with their function, rat OCT1 and OCT2 were localized to the basolateral membrane of proximal tubule ce...

Interactions of Human- and Rat-Organic Anion Transporters With Pravastatin and Cimetidine

“…Thus, the results of studies using cimetidine as an OCT inhibitor have to be carefully interpreted considering the effect of this substrate on the OAT system. Burkhardt et al (2003) have already demonstrated that hOAT1 mediated the uptake of cimetidine (17). However, we noted that cimetidine inhibited the PAH uptake mediated by hOAT1 in a combination of competitive and noncompetitive manners.…”

Relative contribution of OAT and OCT transporters to organic electrolyte transport in rabbit proximal tubule

“…Figure 8 shows the effect of 1 mM concentrations of unlabeled PAH and CIM on the uptake of radiolabeled PAH and CIM into CHO cells that stably expressed rbOAT1. PAH (1 mM), as expected, reduced accumulation of 0.3 M [ observed by Burckhardt et al (7). As shown in Fig.…”

“…We also found that the rabbit ortholog of OAT3 interacts with CIM with higher apparent affinity at elevated pH, consistent with the view that the neutral species binds more effectively to the transporter than does the charged species (unpublished observations). However, ES transport showed the same sensitivity to pH, despite the fact that over the tested pH range (pH [7][8] there is no significant change in the concentration of the protonated species of ES. Consequently, it remains equivocal if the charge status of CIM plays a role in its binding to rabbit OAT3.…”

“…In that study, binding to hOCT2 of compounds that have a fixed cationic charge (e.g., TEA and MPP) was shown to be insensitive to ambient pH, whereas interaction of weak bases (including CIM) shifted in direct proportion to their pH-sensitive charge status. If, as suggested by Burckhardt et al (7), OATs interact preferentially with CIM 0 , and OCTs interact with CIM ϩ , then a change in ambient pH could simply increase the effective concentration of substrate for one set of transporters (e.g., OATs), while reducing the concentration of substrate for the other set (e.g., OCTs).…”

Competitive inhibition of renal tubular secretion of ciprofloxacin and metabolite by probenecid

“…As a zwitterion at physiological pH values (pKa1 = 6.1, pKa2 = 8.7), ciprofloxacin might also be able to interact with both OAT and OCT [23]. Cimetidine, an inhibitor of OCT as well as OAT 1 and 3 [24][25][26], has been shown to decrease the renal clearance of several quinolones, e.g. gemifloxacin, enoxacin, temafloxacin and ofloxacin [27,28].…”