σ-1 Receptor Modulation of Acid-Sensing Ion Channel a (ASIC1a) and ASIC1a-Induced Ca²⁺ Influx in Rat Cortical Neurons

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 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

Activation of Acid-sensing Ion Channel 1a (ASIC1a) by Surface Trafficking

“…The interaction between TASK-1 and p11 is intriguing because p11 binding causes release of the channel from the ER by masking the retention signal. An ER membrane protein sigma-1 receptor (Sig-1R) has also been identified as a modulator of ASIC1a activity, by which inhibition of this protein activated ASIC1a channel (37). Although the underlying mechanisms are unknown, association of p11 and Sig-1R with ASIC1a activity points to regulation of this channel at the ER level.…”

Afobazole Modulates Microglial Function via Activation of Both σ-1 and σ-2 Receptors

“…Microglia plated on glass coverslips were moved to a recording chamber mounted on a Zeiss Axiovert 200 and visualized at 400ϫ. Methods for the electrical recordings of these cells were identical to those used previously in our laboratory to record from neurons (Herrera et al, 2008). Cells were electrically accessed using the amphotericin B-perforated patch method (Rae et al, 1991).…”

Detergent-Resistant Microdomains Determine the Localization of σ-1 Receptors to the Endoplasmic Reticulum-Mitochondria Junction

“…For example, Sig-1R chaperones stabilize the conformation of MAM-residing type-3 inositol 1,4,5-trisphosphate receptors (IP3R3), thus regulating the Ca 2ϩ influx from the ER to mitochondria (Hayashi et al, 2009). On the other hand, a number of studies demonstrate that Sig1Rs also regulate cellular events at plasma membranes, such as neurotransmitter release, neurotrophic factor signaling, and opening of voltage-gated ion channels (Aydar et al, 2002;Nuwayhid and Werling, 2003;Hayashi and Su, 2008;Herrera et al, 2008). The tonic inhibition of the potassium Kv1.4 channel by Sig-1Rs involves the physical association between Sig-1R and Kv1.4 channels (Aydar et al, 2002).…”