Acid-sensing ion channels (ASICs) are proton-gated cation channels found in peripheral and central nervous system neurons. The ASIC1a subtype, which has high Ca 2ϩ permeability, is activated by ischemia-induced acidosis and contributes to the neuronal loss that accompanies ischemic stroke. Our laboratory has shown that activation of receptors depresses ion channel activity and [Ca 2ϩ ] i dysregulation during ischemia, which enhances neuronal survival. Whole-cell patch-clamp electrophysiology and fluorometric Ca 2ϩ imaging were used to determine whether receptors regulate the function of ASIC in cultured rat cortical neurons. Bath application of the selective ASIC1a blocker, psalmotoxin1, decreased proton-evoked [Ca 2ϩ ] i transients and peak membrane currents, suggesting the presence of homomeric ASIC1a channels. The pan-selective -1/-2 receptor agonists, 1,3-di-o-tolyl-guanidine (100 M) and opipramol (10 M), reversibly decreased acid-induced elevations in [Ca 2ϩ ] i and membrane currents. Pharmacological experiments using receptor-subtype-specific agonists demonstrated that -1, but not -2, receptors inhibit ASIC1a-induced Ca 2ϩ elevations. These results were confirmed using the irreversible receptor antagonist metaphit (50 M) and the selective -1 antagonist BD1063 (10 nM), which obtunded the inhibitory effects of the -1 agonist, carbetapentane. Activation of ASIC1a was shown to stimulate downstream Ca 2ϩ influx pathways, specifically N-methyl-D-aspartate and (Ϯ)-␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate receptors and voltage-gated Ca 2ϩ channels. These subsequent Ca 2ϩ influxes were also inhibited upon activation of -1 receptors. These findings demonstrate that -1 receptor stimulation inhibits ASIC1a-mediated membrane currents and consequent intracellular Ca 2ϩ accumulation. The ability to control ionic imbalances and Ca 2ϩ dysregulation evoked by ASIC1a activation makes receptors an attractive target for ischemic stroke therapy.Acid-sensing ion channels are a class of ligand-gated channels that are members of the degenerin/epithelial sodium channel superfamily and are expressed in both peripheral and central nervous system neurons . Thus far, four genes (ASIC1-ASIC4) and two splice variants of ASIC1 and ASIC2 (a and b) have been cloned ) that encode protein subunits that form functional proton-gated homomultimeric or heteromultimeric channels . The pH of half-maximal activation and the tissue expression patterns differ between each channel subtype.One of the most common ASIC subtypes in the central nervous system (CNS) contains the ASIC1a subunit, which can form homomultimeric or heteromultimeric channels with ASIC2a . These channels are activated by pH Յ 7 and have a pH of half-maximal activation of ϳ6.0