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.
|Number of pages||12|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Nov 2008|
ASJC Scopus subject areas
- Molecular Medicine