Abstract
Haloperidol is known as an antagonist of dopamine D2 receptors. However, it also blocks a variety of ion channels at concentrations above the therapeutic range. Reduced haloperidol (R-haloperidol), one of the main metabolites of haloperidol, has been reported to accumulate in certain tissues, particularly in brain cortex, and it may produce the pharmacological effects associated with haloperidol treatment. In this study, we assessed the effect of R-haloperidol and other related compounds on native delayed-rectifier potassium channels (KDR) in mouse cortical neurons by using the whole-cell patch-clamp technique. Although R-haloperidol has much lower affinity to D2 receptors than haloperidol, the IC50 of R-haloperidol to block KDR currents was 4.4 μM, similar to its parent compound. The binding site of R-haloperidol is on the cytoplasmic side of the channel because its quaternary derivative preferentially inhibited the currents from intracellular side. 4-Chlorophenyl-4-hydroxypiperidine (4C4HP) is the active fragment of haloperidol because other compounds containing this moiety, including L-741,626 (3-[4-(4-chlorophenyl)-4-hydroxypiperidin-l-yl]-methyl-1H-indole) and loperamide, also blocked KDR channels. The potency of the 4C4HP fragment positively correlated with the hydrophobicity index (clogP) of the compounds tested. We conclude that R-haloperidol is a KDR channel blocker, although it does not interfere with the normal channel function at a clinically relevant concentration.
Footnotes
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S.-B.Y. is a Ph.D. student of the International M.D./Ph.D. Program in the Neurosciences of the International Max Planck Research School in Göttingen, Germany.
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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.105.086561.
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ABBREVIATIONS: HERG, human ether-a-go-go-related gene; KDR, delayed-rectifier potassium channel(s); 4C4HP, 4-chlorophenyl-4-hydroxypiperidine; 3FBPA, 3-fluorobenzoyl propionic acid; R-haloperidol, reduced haloperidol; 4-AP, 4-aminopyridine; L-741,626, 3-[4-(4-chlorophenyl)-4-hydroxypiperidin-l-yl]methyl-1H-indole; N-Me-R-haloperidol, N-methyl-reduced haloperidol.
- Received March 18, 2005.
- Accepted July 7, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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