Abstract
In the central nervous system (CNS), brain macrophages and microglia are the primary targets of productive human immunodeficiency virus 1 (HIV-1) infection. Zidovudine (ZDV), a thymidine derivative, has been reported to reduce the progression of the disease and prolong survival in patients with acquired immunodeficiency syndrome (AIDS) and AIDS dementia complex. Although a restricted ZDV distribution has been observed in the CNS, its accumulation in brain parenchyma has not been examined. We have investigated the uptake properties of radiolabeled ZDV by a continuous rat microglia cell line (MLS-9) grown as a monolayer on an impermeable surface. Although the organic cations verapamil, mepiperphenidol, quinidine, cimetidine, andN1-methylnicotinamide moderately inhibited ZDV uptake, the organic cation probes tetraethylammonium and 1-methyl-4-phenylpyridinium were weak inhibitors. ZDV uptake was significantly increased when the proton gradient was outward (pHi 6.3 < pHo 7.4; pHi∼7.1 < pH 8.0), whereas uptake decreased with extracellular acidification (pHi ∼7.1 > pHo 6.0) or in the presence of the Na+/H+ ionophore monensin. ZDV uptake was increased under depolarized membrane conditions (i.e., 138 mM K+ in external medium) and decreased under hyperpolarized conditions (i.e., 2 mM K+ in external medium), implying a membrane potential dependence. These results suggest that although ZDV transport system in microglia has some specificity features of an organic cation transporter, it involves a carrier, distinct from other cloned organic cation transporters, that is novel in its sensitivity to pH and membrane potential. This system may play a significant role in the transport of other weak organic cation substrates and/or metabolites in brain parenchyma.
Footnotes
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Send reprint requests to: Dr. Reina Bendayan, Department of Pharmaceutical Sciences, Faculty of Pharmacy, University of Toronto, 19 Russell St., Toronto, Ontario M5S 2S2, Canada. E-mail:r.bendayan{at}utoronto.ca
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↵1 Current address: Department of Pharmaceutical Sciences, Faculty of Pharmacy, University of Toronto, Toronto, Ontario M5S 2S2, Canada.
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↵2 Current address: Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario M5T 2S8 and Department of Physiology and Institute for Medical Sciences, University of Toronto, Toronto, Ontario M5S 1A1, Canada.
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This work was supported by a grant from the Ontario HIV Treatment Network (OHTN), the Canadian Foundation for AIDS Research (CANFAR), the Glaxo Wellcome Positive Action Fund, Ontario Ministry of Health, and the Heart and Stroke Foundation of Ontario (no. T3726). M.H. is a recipient of an Ontario HIV Treatment Network Studentship Award.
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This work was presented in preliminary form (Hong et al., 1999). Poster presented at the 1999 Annual Meeting of the American Association of Pharmaceutical Scientists, New Orleans, LA, Nov. 1999.
- Abbreviations:
- HIV-1
- human immunodeficiency virus 1
- AIDS
- acquired immunodeficiency syndrome
- ADC
- AIDS dementia complex
- CNS
- central nervous system
- ZDV
- zidovudine
- BBB
- blood-brain barrier
- CSF
- cerebrospinal fluid
- EBSS
- Earle's balanced saline solution
- MES
- 2-(N-morpholino)ethanesulfonic acid
- BCECF
- 2′,7′-bis(carboxyethyl)-5(6′-carboxyfluorescein
- BCECF-AM
- 2′,7′-bis(carboxyethyl)-5(6′-carboxyfluorescein acetoxymethyl ester
- MPP+
- 1-methyl-4-phenylpyridinium
- TEA
- tetraethylammonium
- OCT
- organic cation transport
- BES
- N,N-bis(2-hydroxyethyl]-2-aminoethanesulfonic acid
- Received May 19, 2000.
- Accepted September 19, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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