Effect of 3'-azido-3'-deoxythymidine on organic ion transport in rat renal plasma membrane vesicles
Abstract
3$\sp\prime$-Azido-3$\sp\prime$-deoxythymidine (AZT), a nucleoside analog which has potent activity against the AIDS virus, is rapidly cleared by the mammalian kidney. To clarify the mechanism of renal drug transport, and with the knowledge that AZT is cleared primarily by active secretion, we examined the effect of AZT on organic ion transport systems. Specifically, the effect of AZT on prototypic substrates for the organic cation transporter, ($\sp3$H) N$\sp1$-methylnicotinamide (NMN) and ($\sp3$H) tetraethylammonium (TEA) and the organic anion transporter, ($\sp3$H) p-aminohippurate (PAH) were examined by employing a rapid filtration assay in rat renal basolateral membrane vesicles (BLMV) and brush border membrane vesicles (BBMV). In rat BLMV, AZT was capable of inhibiting uptake of ($\sp3$H) PAH. The dose response curves for AZT and probenecid (PRO) revealed IC$\sb{50}$ values of 225$\mu$M and 15$\mu$M, respectively. In counterflow studies, AZT trans stimulated uptake of PAH. Kinetic data confirmed that both AZT and PRO inhibited PAH transport at the basolateral membrane (BLM) in a competitive manner. AZT did not inhibit uptake of ($\sp3$H) NMN nor ($\sp3$H) TEA. Under optimized conditions which employed BLMV loaded with TEA, AZT did inhibit uptake of ($\sp3$H) TEA. We conclude that AZT transport in rat BLMV is mediated predominantly by the renal organic anion transport system. In rat BBMV AZT inhibited NMN transport. The dose-response curves for AZT and mepiperphenidol (MEPI) produced IC$\sb{50}$ values of 2500$\mu$M and 25$\mu$M, respectively. Counterflow studies revealed that TEA and MEPI trans stimulated TEA uptake, but AZT did not. To clarify the actions of AZT, kinetic studies were undertaken. The data revealed that both AZT and MEPI inhibited NMN transport at the brush border membrane (BBM) in a competitive manner. AZT did not block PAH transport. We conclude that AZT transport in rat BBMV is mediated by the renal organic cation transport system. We explored the relationship between the nucleoside transporter and classical renal organic cation transporter in rat BBMV. Thymidine (THY), a pyrimidine nucleoside, inhibited uptake of ($\sp3$H) NMN with an IC$\sb{50}$ value of 420$\mu$M. Likewise kinetic data revealed that THY inhibited transport of NMN at the BBM in a competitive manner. Since AZT is an analog of THY, active secretion of AZT at the BBM may be occurring via the nucleoside transporter.
Degree
Ph.D.
Advisors
Kildsig, Purdue University.
Subject Area
Pharmacology|Pharmaceuticals|Pharmacology
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