Classic D1 Dopamine Receptor Antagonist R-(+)-7-Chloro-8- hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine hydrochloride (SCH23390) Directly Inhibits G Protein-Coupled Inwardly Rectifying Potassium Channels ELDO V. KUZHIKANDATHIL 1 and GERRY S. OXFORD Department of Cell and Molecular Physiology and the Neuroscience Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina Received December 13, 2001; accepted April 8, 2002 This article is available online at http://molpharm.aspetjournals.org ABSTRACT R-(+)-7-Chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahy- dro-1H-3-benzazepine hydrochloride (SCH23390) is a widely used, highly selective antagonist of D1 dopamine receptors. While investigating the crosstalk between D1 and D3 dopamine receptor signaling pathways, we discovered that in addition to being a D1 receptor antagonist, SCH23390 and related com- pounds inhibit G protein-coupled inwardly rectifying potassium (GIRK) channels. We present evidence that SCH23390 blocks endogenous GIRK currents induced by either somatostatin or D3 dopamine receptors in AtT-20 cells (IC 50 , 268 nM). The inhibition is receptor-independent because constitutive GIRK currents in Chinese hamster ovary cells expressing only GIRK channels are also blocked by SCH23390. The inhibition of GIRK channels is somewhat selective because members of the closely related Kir2.0 family of inwardly rectifying potassium channels, as well as various endogenous cationic currents present in AtT-20 cells, are not affected. In addition, in current clamp recordings, SCH23390 can depolarize the membrane potential and induce AtT-20 cells to fire action potentials, indi- cating potential physiological significance of the GIRK channel inhibition. To identify the chemical features that contribute to GIRK channel block, we tested several structurally related compounds [SKF38393, R-(+)-7-chloro-8-hydroxy-1-phenyl- 2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (nor- methyl-SCH23390), and R-(+)-2,3,4,5-tetrahydro-8-iodo-3- methyl-5-phenyl-1H-3-benzazepin-7-ol hydrochloride (iodo- SCH23390)], and our results indicate that the halide atom is critical for blocking GIRK channels. Taken together, our results suggest that SCH23390 and related compounds might provide the basis for designing novel GIRK channel-selective blockers. Perhaps more importantly, some studies that have exclusively used SCH23390 to probe D1 receptor function or as a diag- nostic of D1 receptor involvement may need to be reevaluated in light of these results. We have previously shown that the D3 dopamine receptor couples to and activates G protein-coupled inwardly rectify- ing potassium (GIRK) channels (Werner et al., 1996; Kuzhi- kandathil et al., 1998) and inhibits P/Q-type calcium chan- nels (Kuzhikandathil and Oxford, 1999). Given the coexpression of D1 and D3 dopamine receptors in central nervous system neurons, particularly in a subset of nucleus accumbens neurons (Le Moine and Bloch, 1996), we were interested in exploring the functional consequence of D1 re- ceptor activation on D3 receptor–GIRK channel coupling. To address this issue, we used two ligands that are highly se- lective for D1 receptors and have long served as diagnostic probes of D1 receptor function. One of these ligands, R-(+)- 7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro- 1H-3-benzazepine hydrochloride (SCH23390), is a highly se- lective antagonist of D1 dopamine receptors with at least a 1000-fold higher affinity for D1 receptors than for D3 recep- tors (Iorio et al., 1983; Neve and Neve, 1997). SCH23390 is a member of the phenyltetrahydrobenzazepines, a structural class that also includes the partial D1 agonist R-(+)-1- phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol hydro- chloride (SKF38393). SCH23390 has been widely used both in vivo and in vitro to characterize D1 receptor function and This work was supported by National Institutes of Health grant NS18788 (to G.S.O.) and a Howard Hughes Medical Institute Pilot Studies grant (to E.V.K.). 1 Current address: Department of Pharmacology and Physiology, UMDNJ- New Jersey Medical School, Newark, NJ 07103. ABBREVIATIONS: GIRK, G protein-coupled inwardly rectifying potassium channel; SCH23390, R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl- 2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride; SKF38393, R-(+)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol hydrochloride; nor-methyl-SCH23390, R-(+)-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride; iodo-SCH23390, R-(+)-2,3,4,5- tetrahydro-8-iodo-3-methyl-5-phenyl-1H-3-benzazepin-7-ol hydrochloride; U50488H, trans-()-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]cyclo- hexyl)benzeneacetamide; VTA, ventral tegmental area; QP, quinpirole; CHO, Chinese hamster ovary cells; 30 K-ES, 30 mM potassium. 0026-895X/02/6201-119 –126$7.00 MOLECULAR PHARMACOLOGY Vol. 62, No. 1 Copyright © 2002 The American Society for Pharmacology and Experimental Therapeutics 1536/992700 Mol Pharmacol 62:119–126, 2002 Printed in U.S.A. 119 at ASPET Journals on May 24, 2017 molpharm.aspetjournals.org Downloaded from