Involvement of Acid-Sensing Ion Channel 1b in the Development of Acid-Induced Chronic Muscle Pain

Abstract

Acid-sensing ion channels (ASICs) are important acid sensors involved in neural modulation in the central nervous system and pain-associated tissue acidosis in the peripheral system. Among ASIC subtypes, ASIC1b is the most selectively expressed in peripheral sensory neurons. However, the role of ASIC1b is still elusive in terms of its functions and expression profile. In this study, we probed the role of ASIC1b in acid-induced muscle pain in Asic1b-knockout (Asic1b–/–) and Asic1b-Cre transgenic (Asic1bCre) mice. We tested the effect of ASIC1b knockout in a mouse model of fibromyalgia induced by dual intramuscular acid injections. In this model, a unilateral acid injection to the gastrocnemius muscle induced transient bilateral hyperalgesia in wild-type (Asic1b+/+) but not Asic1b–/– mice; a second acid injection, spaced 1 or 5 days apart, to the same muscle induced chronic hyperalgesia lasting for 4 weeks in Asic1b+/+ mice, but the duration of hyperalgesia was significantly shortened in Asic1b–/– mice. Mambalgin-1, an ASIC1b-containing channel inhibitor that was mixed with acid saline at the first injection, dose-dependently blocked the acid-induced transient and chronic hyperalgesia in Asic1b+/+ mice. In contrast, psalmotoxin 1 (PcTx1), an ASIC1a-selective antagonist, had no effect on acid-induced transient or chronic hyperalgesia. We used whole-cell patch clamp recording to study the properties of acid-induced currents in ASIC1b-expressing dorsal root ganglia (DRG) neurons from Asic1bCre-TdTomato reporter mice. Medium- to large-sized ASIC1b-expressing DRG neurons mainly exhibited an amiloride-sensitive ASIC-like biphasic current (IASIC) in response to acid stimulation, whereas small- to medium-sized ASIC1b-expressing DRG neurons predominantly exhibited an amiloride-insensitive sustained current. Specifically, mambalgin-1 selectively inhibited the IASIC in most ASIC1b-expressing DRG neurons. However, PcTx1 or APETx2 (an ASIC3-selective antagonist) had only a mild inhibitory effect on IASIC in about half of the ASIC1b-expressing DRG neurons. In situ hybridization revealed that ASIC1b-positive DRG neurons co-expressed highly with ASIC1a and ASIC2a mRNA and partially with ASIC3 and ASIC2b. Thus, ASIC1b might form a wide variety of heteromeric channels. ASIC1b-containing heteromeric channels might be promising targets for the therapeutic treatment of acid-induced chronic muscle pain.

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“…This demonstrated for the first time that ASIC1b-containing channels in rodent nociceptors, as opposed to the splice isoform ASIC1a, are important for peripheral analgesia. More recent work using an ASIC1b knockout animal confirmed the role of this subtype in peripheral pain sensing [78]. In this model, peripheral injection of mambalgin had no effect on acid-induced hyperalgesia in ASIC1b knockout mice.…”

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“…Local injection of the same dose (~0.1 mg/kg) also produced a significant analgesic effect on acute heat pain and reversed carrageenan-induced inflammatory hyperalgesia via ASIC1b ( Diochot et al., 2012 ). An intravenous administration 15-30 pmol/mouse (~0.005–0.01 mg/kg dose) of mambalgin-1 was reported to produce a significant analgesic effect in models of acid-induced mechanical hyperalgesia, thus confirming ASIC1b as a perspective pharmacological target on peripheral neurons ( Chang et al., 2019 ).…”

“…In particular, interesting results were obtained in showing that ASIC1a subtypes play an important role in retinal activity ( Ettaiche, 2006 ). Also, due to the successful selective inhibition of the ASIC1a subtype, it was shown that ASIC1b is involved in the development of muscle pain ( Chang et al., 2019 ) and that the ASIC3 subtype is responsible for postoperative pain ( Deval et al., 2011 ).…”

“…Mambalgins are “multitarget” peptides from the venom of the black mamba and block heteromeric channels of ASIC1a and ASIC2a subunits in CNS neurons and ASIC1b-containing channels in peripheral sensory neurons. Mambalgins relieve the pain in several ways through inhibition of different subtypes of ASICs expressed both in central and peripheral neurons ( Diochot et al., 2012 ; Diochot et al., 2016 ; Chang et al., 2019 ). Mambalgins intrathecal administration of ~340 pmol/mouse (~0.1 mg/kg dose) efficiently reduced different types of pain (e.g., acute heat pain, inflammatory hyperalgesia, formalin-induced pain) through an opioid-independent pathway involving ASIC1a and ASIC2a channels.…”

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“…Classified as a specific inhibitor of ASIC1a, the most abundant acid-sensing ion channel, the toxin π-TRTX-Pc1 demonstrated an effective analgesic effect comparable to morphine in rat models of acute pain ( Mazzuca et al., 2007 ). Recently, PcTx1 was also reported as a valuable tool for understanding the functional role of ASIC2a heteromeric channels (ASIC1a/2a) ( Liu et al., 2018 ) and had no effect on acid-induced transient or chronic hyperalgesia in a mouse model of fibromyalgia ( Chang et al., 2019 ).…”