Abstract
Acid-sensing ion channels (ASICs) are proton-gated cation channels found in peripheral and central nervous system neurons. The ASIC1a subtype, which has high Ca2+ permeability, is activated by ischemia-induced acidosis and contributes to the neuronal loss that accompanies ischemic stroke. Our laboratory has shown that activation of σ receptors depresses ion channel activity and [Ca2+]i dysregulation during ischemia, which enhances neuronal survival. Whole-cell patch-clamp electrophysiology and fluorometric Ca2+ imaging were used to determine whether σ receptors regulate the function of ASIC in cultured rat cortical neurons. Bath application of the selective ASIC1a blocker, psalmotoxin1, decreased proton-evoked [Ca2+]i transients and peak membrane currents, suggesting the presence of homomeric ASIC1a channels. The pan-selective σ-1/σ-2 receptor agonists, 1,3-di-o-tolyl-guanidine (100 μM) and opipramol (10 μM), reversibly decreased acid-induced elevations in [Ca2+]i and membrane currents. Pharmacological experiments using σ receptor-subtype-specific agonists demonstrated that σ-1, but not σ-2, receptors inhibit ASIC1a-induced Ca2+ elevations. These results were confirmed using the irreversible σ receptor antagonist metaphit (50 μM) and the selective σ-1 antagonist BD1063 (10 nM), which obtunded the inhibitory effects of the σ-1 agonist, carbetapentane. Activation of ASIC1a was shown to stimulate downstream Ca2+ influx pathways, specifically N-methyl-d-aspartate and (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate receptors and voltage-gated Ca2+ channels. These subsequent Ca2+ influxes were also inhibited upon activation of σ-1 receptors. These findings demonstrate that σ-1 receptor stimulation inhibits ASIC1a-mediated membrane currents and consequent intracellular Ca2+ accumulation. The ability to control ionic imbalances and Ca2+ dysregulation evoked by ASIC1a activation makes σ receptors an attractive target for ischemic stroke therapy.
Footnotes
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This study was supported by an American Heart Association Florida/Puerto Rico Affiliate Grant-In-Aid Award and by a University of South Florida Signature Program in Neuroscience Award (to J.C.).
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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.108.143974.
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ABBREVIATIONS: ASIC, acid-sensing ion channel; CNS, central nervous system; NMDA, N-methyl-d-aspartate; AMPA, (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid; VGCC, voltage-gated Ca2+ channel; PSS, physiological saline solution; DTG, 1,3-di-o-tolyl-guanidine; nifedipine, 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinedicarboxylic acid dimethyl ester; AP5, d-2-amino-5-phosphonovaleric acid; PB28, 1-cyclohexyl-4-(3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)-n-propyl)piperazine dihydrochloride; BD1063, 1-[2-(3,4-dichlorophenyl)-ethyl]-4-methylpiperazine dihydrochloride; CNQX, 6-cyano-7-nitroquinoxaline-2,3-dione; PRE-084, 2-(4-morpholinethyl) 1-phenylcyclohexane-carboxylate hydrochloride; PcTx1, psalmotoxin1; CBP, carbetapentane citrate; DEX, dextromethorphan hydrobromide; MET, metaphit; IBO, ibogaine; THAP, thapsigargin; TTX, tetrodotoxin.
- Received July 23, 2008.
- Accepted August 21, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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