Abstract
Intoxication with γ-hydroxybutyrate (GHB) is associated with coma, seizure, and death; treatment of overdoses is symptomatic. Previous studies in our laboratory have demonstrated that l-lactate and pyruvate treatment can increase the renal clearance of GHB and increase its elimination in rats, suggesting that GHB may undergo renal reabsorption mediated by monocarboxylic acid transporters (MCTs). The goals of this study were to characterize the renal transport of GHB in rats and to determine the role of MCT in its renal transport. Brush-border membrane (BBM) and basolateral membrane (BLM) vesicles were isolated from rat kidney cortex, and the uptake of l-lactate and GHB was characterized. l-Lactate and GHB undergo both pH- and sodium-dependent transport in BBM vesicles and pH-dependent transport in BLM vesicles. A simple Michaelis-Menten equation best described the pH-dependent uptake of GHB in BBM (Km, 8.0 ± 1.8 mM; Vmax, 838 ± 45 pmol/mg/s) and in BLM vesicles (Km, 10.5 ± 2.6 mM; Vmax, 806 ± 253 pmol/mg/s). mRNA of MCT1 and MCT2 was determined in rat kidney cortex using reverse transcriptase-polymerase chain reaction; using Western blot, the protein expression of MCT1 was present mainly in BLM vesicles, with weak expression in BBM vesicles, whereas that of MCT2 was exclusively in BLM vesicles. Studies with rat MCT1 gene-transfected MDA-MB231 cells demonstrated that GHB was a substrate of MCT1. The data suggest that rat MCT1 may represent an important transporter for GHB in renal tubule cells. This investigation provides evidence for the importance of MCTs in the reabsorption of the monocarboxylic acids l-lactate and GHB in the kidney.
Footnotes
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This work was supported by National Institutes of Health Grant DA14988 and by a grant from the Western New York Kidney Foundation/Upstate New York Transplantation Service.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.105965.
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ABBREVIATIONS: GHB, γ-hydroxybutyrate; MCT, monocarboxylate transporter; BBM, brush-border membrane; BLM, basolateral membrane; AA, acetoacetate; BHB, β-hydroxybutyrate; BTD, 1,4-butanediol; CHC, α-cyano-4-hydroxycinnamate; DIDS, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid disodium salt; TEA, tetraethylammonium; MES, 2-(N-morpholino)ethanesulfonic acid; ALP, alkaline phosphatase; GGT, γ-glutamyl transferase; RT, reverse transcriptase; PCR, polymerase chain reaction; ANOVA, analysis of variance; bp, base pair(s); GBL, γ-butyrolactone.
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↵1 Current affiliation: Cognigen Corporation, Buffalo, New York.
- Received April 9, 2006.
- Accepted May 16, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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