Adenosine triphosphate (ATP) is well-known as a universal source of energy in living cells. Less known is that this molecule has a variety of important signaling functions: it activates a variety of specific metabotropic (P2Y) and ionotropic (P2X) receptors in neuronal and non-neuronal cell membranes. So, a wide variety of signaling functions well fits the ubiquitous presence of ATP in the tissues. Even more ubiquitous are protons. Apart from the unspecific interaction of protons with any protein, many physiological processes are affected by protons acting on specific ionotropic receptors-acid-sensing ion channels (ASICs). Both protons (acidification) and ATP are locally elevated in various pathological states. Using these fundamentally important molecules as agonists, ASICs and P2X receptors signal a variety of major brain pathologies. Here we briefly outline the physiological roles of ASICs and P2X receptors, focusing on the brain pathologies involving these receptors.
Humans ; Acid Sensing Ion Channels ; Protons ; Neurons ; Brain Diseases ; Adenosine Triphosphate/physiology*

Mechanosensitive ion channels (MSCs) are key molecules in the mechano-electrical transduction of arterial baroreceptors. Among them, acid-sensing ion channel 2 (ASIC2) and transient receptor potential vanilloid subfamily member 1 (TRPV1) have been studied extensively and documented to play important roles. In this study, experiments using aortic arch-aortic nerve preparations isolated from rats revealed that both ASIC2 and TRPV1 are functionally necessary, as blocking either abrogated nearly all pressure-dependent neural discharge. However, whether ASIC2 and TRPV1 work in coordination remained unclear. So we carried out cell-attached patch-clamp recordings in HEK293T cells co-expressing ASIC2 and TRPV1 and found that inhibition of ASIC2 completely blocked stretch-activated currents while inhibition of TRPV1 only partially blocked these currents. Immunofluorescence staining of aortic arch-aortic adventitia from rats showed that ASIC2 and TRPV1 are co-localized in the aortic nerve endings, and co-immunoprecipitation assays confirmed that the two proteins form a compact complex in HEK293T cells and in baroreceptors. Moreover, protein modeling analysis, exogenous co-immunoprecipitation assays, and biotin pull-down assays indicated that ASIC2 and TRPV1 interact directly. In summary, our research suggests that ASIC2 and TRPV1 form a compact complex and function synergistically in the mechano-electrical transduction of arterial baroreceptors. The model of synergism between MSCs may have important biological significance beyond ASIC2 and TRPV1.
Acid Sensing Ion Channels/physiology* ; Animals ; HEK293 Cells ; Humans ; Pressoreceptors/physiology* ; Rats ; TRPV Cation Channels/physiology*

OBJECTIVE: To investigate the effects of acid-sensing ion channels (ASICs) on electrophysiological epileptic activities of mouse hippocampal pyramidal neurons in the extracellular acidotic condition. METHODS: We investigated effects of extracellular acidosis on epileptic activities induced by elevated extracellular K concentration or the application of an antagonist of GABA receptors in perfusate of mouse hippocampal slices under field potential recordings. We also tested the effects of extracellular acidosis on neuronal excitability under field potential recording and evaluated the changes in epileptic activities of the neurons in response to pharmacological inhibition of ASICs using a specific inhibitor of ASICs. RESULTS: Extracellular acidosis significantly suppressed epileptic activities of the hippocampal neurons by converting ictal-like epileptic activities to non-ictal-like epileptic activities in both high [K ]o and disinhibition models, and also suppressed the intrinsic excitability of the neurons. ASICs inhibitor did not antagonize the inhibitory effect of extracellular acidosis on ictal epileptic activities and intrinsic neuronal excitability, but exacerbated non-ictal epileptic activities of the neurons in extracellular acidotic condition in both high [K]o and disinhibition models. CONCLUSIONS ASICs can differentially modulate ictal-like and non-ictallike epileptic activities via its direct actions on excitatory neurons.
Acid Sensing Ion Channels ; metabolism ; Acidosis ; Animals ; Epilepsy ; physiopathology ; Hydrogen-Ion Concentration ; Mice ; Pyramidal Cells ; pathology ; physiology

OBJECTIVE: To investigate the effects of acid-sensing ion channels (ASICs) on electrophysiological epileptic activities of mouse hippocampal pyramidal neurons in the extracellular acidotic condition. METHODS: We investigated effects of extracellular acidosis on epileptic activities induced by elevated extracellular K concentration or the application of an antagonist of GABA receptors in perfusate of mouse hippocampal slices under field potential recordings. We also tested the effects of extracellular acidosis on neuronal excitability under field potential recording and evaluated the changes in epileptic activities of the neurons in response to pharmacological inhibition of ASICs using a specific inhibitor of ASICs. RESULTS: Extracellular acidosis significantly suppressed epileptic activities of the hippocampal neurons by converting ictal-like epileptic activities to non-ictal-like epileptic activities in both high [K ]o and disinhibition models, and also suppressed the intrinsic excitability of the neurons. ASICs inhibitor did not antagonize the inhibitory effect of extracellular acidosis on ictal epileptic activities and intrinsic neuronal excitability, but exacerbated non-ictal epileptic activities of the neurons in extracellular acidotic condition in both high [K]o and disinhibition models. CONCLUSIONS ASICs can differentially modulate ictal-like and non-ictallike epileptic activities via its direct actions on excitatory neurons.
Acid Sensing Ion Channels ; Acidosis ; Animals ; Hippocampus ; Hydrogen-Ion Concentration ; Mice ; Pyramidal Cells

This study aims to validate our hypothesis that acid-sensing ion channels (ASICs) may contribute to the symptom of pain in patients with chronic prostatitis (CP). We first established a CP rat model, then isolated the L5-S2 spinal dorsal horn neurons for further studies. ASIC1a was knocked down and its effects on the expression of neurogenic inflammation-related factors in the dorsal horn neurons of rat spinal cord were evaluated. The effect of ASIC1a on the Ca²⁺ ion concentration in the dorsal horn neurons of rat spinal cord was measured by the intracellular calcium ([Ca²⁺]i) intensity. The effect of ASIC1a on the p38/mitogen-activated protein kinase (MAPK) signaling pathway was also determined. ASIC1a was significantly upregulated in the CP rat model as compared with control rats. Acid-induced ASIC1a expression increased [Ca²⁺]i intensity in the dorsal horn neurons of rat spinal cord. ASIC1a also increased the levels of neurogenic inflammation-related factors and p-p38 expression in the acid-treated dorsal horn neurons. Notably, ASIC1a knockdown significantly decreased the expression of pro-inflammatory cytokines. Furthermore, the levels of p-p38 and pro-inflammatory cytokines in acid-treated dorsal horn neurons were significantly decreased in the presence of PcTx-1, BAPTA-AM, or SB203580. Our results showed that ASIC1a may contribute to the symptom of pain in patients with CP, at least partially, by regulating the p38/MAPK signaling pathway.
Acid Sensing Ion Channel Blockers/pharmacology* ; Acid Sensing Ion Channels/genetics* ; Animals ; Calcium/metabolism* ; Chelating Agents/pharmacology* ; Chronic Disease ; Cytokines/metabolism* ; Disease Models, Animal ; Egtazic Acid/pharmacology* ; Gene Knockdown Techniques ; Imidazoles/pharmacology* ; Inflammation/metabolism* ; MAP Kinase Signaling System/genetics* ; Male ; Pain/genetics* ; Peptides/pharmacology* ; Phosphorylation/drug effects* ; Posterior Horn Cells/metabolism* ; Prostatitis/complications* ; Protein Kinase Inhibitors/pharmacology* ; Pyridines/pharmacology* ; Rats ; Spider Venoms/pharmacology* ; Up-Regulation ; p38 Mitogen-Activated Protein Kinases/metabolism*

Protons are widespread in cells and serve a variety of important functions. In certain pathological conditions, acid-base balance was disrupted and therefore excessive protons were generated and accumulated, which is termed acidosis and proved toxic to the organism. In the nervous system, it has been reported that acidosis was a common phenomenon and contributed to neuronal injury in various kinds of neurological diseases, such as ischemic stroke, multiple sclerosis and Huntington's disease. Acid-sensing ion channels (ASICs) is the key receptor of protons and mediates acidosis-induced neuronal injury, but the underlying mechanism remains unclear. Traditionally, Ca(2+) influx through homomeric ASIC1a channels has been considered to be the main cause of acidotoxicity. Recent research showed that extracellular protons trigger a novel form of necroptosis in neurons via ASIC1a-mediated serine/threonine kinase receptor interaction protein 1 (RIP1) activation, independent of ion-conducting function of ASIC1a. In addition, ASIC1a was found in mitochondria and regulated mitochondrial permeability transition-dependent neuronal death. In this article, we will review the recent progresses on the mechanisms underlying ASIC-mediated neuronal death and discuss ASIC modulators involved in this process.
Acid Sensing Ion Channels ; Acid-Base Equilibrium ; Acidosis ; Cell Death ; Neurons ; Neuroprotection

Amiloride and benzamil showed antinocicepitve effects in several pain models through the inhibition of acid sensing ion channels (ASICs). However, their role in neuropathic pain has not been investigated. In this study, we investigated the effect of the intrathecal amiloride and benzamil in neuropathic pain model, and also examined the role of ASICs on modulation of neuropathic pain. Neuropathic pain was induced by L4-5 spinal nerve ligation in male Sprague-Dawley rats weighing 100-120 g, and intrathecal catheterization was performed for drug administration. The effects of amiloride and benzamil were measured by the paw-withdrawal threshold to a mechanical stimulus using the up and down method. The expression of ASICs in the spinal cord dorsal horn was also analyzed by RT-PCR. Intrathecal amiloride and benzamil significantly increased the paw withdrawal threshold in spinal nerve-ligated rats (87%+/-12% and 76%+/-14%, P=0.007 and 0.012 vs vehicle, respectively). Spinal nerve ligation increased the expression of ASIC3 in the spinal cord dorsal horn (P=0.01), and this increase was inhibited by both amiloride and benzamil (P<0.001 in both). In conclusion, intrathecal amiloride and benzamil display antinociceptive effects in the rat spinal nerve ligation model suggesting they may present an alternative pharmacological tool in the management of neuropathic pain at the spinal level.
Acid Sensing Ion Channels/genetics/metabolism ; Amiloride/*analogs & derivatives/pharmacology/*therapeutic use ; Analgesics/pharmacology/*therapeutic use ; Animals ; Disease Models, Animal ; Male ; Neuralgia/*drug therapy ; RNA, Messenger/metabolism ; Rats ; Rats, Sprague-Dawley ; Reverse Transcriptase Polymerase Chain Reaction ; Spinal Cord/metabolism ; Transcription, Genetic/drug effects

In the retina, pH fluctuations may play an important role in adapting retinal responses to different light intensities and are involved in the fine tuning of visual perception. Acidosis occurs in the subretinal space (SRS) under pathological conditions such as age-related macular degeneration (AMD). Although it is well known that many transporters in the retinal pigment epithelium (RPE) cells can maintain pH homeostasis efficiently, other receptors in RPE may also be involved in sensing acidosis, such as acid-sensing ion channels (ASICs). In this study, we investigated whether ASIC1a was expressed in the RPE cells and whether it was involved in the function of these cells. Real-time RT-PCR and Western blotting were used to analyze the ASIC1a expression in ARPE-19 cells during oxidative stress induced by hydrogen peroxide (H(2)O(2)). Furthermore, inhibition or over-expression of ASIC1a in RPE cells was obtained using inhibitors (amiloride and PCTx1) or by the transfection of cDNA encoding hASIC1a. Cell viability was determined by using the MTT assay. The real-time RT-PCR and Western blotting results showed that both the mRNA and protein of ASIC1a were expressed in RPE cells. Inhibition of ASICs by amiloride in normal RPE cells resulted in cell death, indicating that ASICs play an important physiological role in RPE cells. Furthermore, over-expression of ASIC1a in RPE cells prolonged cell survival under oxidative stress induced by H(2)O(2). In conclusion, ASIC1a is functionally expressed in RPE cells and may play an important role in the physiological function of RPE cells by protecting them from oxidative stress.
Acid Sensing Ion Channels ; metabolism ; Cell Line ; Humans ; Ion Channel Gating ; physiology ; Oxidative Stress ; physiology ; Retinal Pigment Epithelium ; cytology ; metabolism

OBJECTIVETo investigate the effects of sufentanil pretreatment on acute gastric mucosal lesion and its impact on the expression of acid-sensing ion channel 3 (ASIC3) in thoracic dorsal root ganglia (DRG) neurons in rats with water immersion-restraint stress (WIRS).

METHODSTwenty-four Wistar rats were randomly assigned into 3 groups, namely the normal control group (n=6), WIRS group (n=12) and sufentanil pretreatment group (n=6). Gastric mucosal lesion was induced by WIRS, and after 6 h of WIRS, the gastric tissues were excised and observed under microscope, with the ulcer index (UI) calculated. The expression of ASIC3 in the DRG neurons was detected by immunofluorescence assay, and the ASIC3 mRNA expression by quantitative real-time RT-PCR.

RESULTSCompared with the normal control group, the rats in the WIRS group showed obvious gastric injury with increased UI and extensive expression of ASIC3 in the DRG neurons. Sufentanil pretreatment of the rats subjected to WIRS significantly alleviated the gastric mucosal injury, lowered the UI, and reduced ASIC3 mRNA expression in thoracic DRG neurons.

CONCLUSIONASIC3 is involved in the development of acute gastric mucosal lesion, and sufentanil pretreatment offers protection of gastric mucosa by inhibiting the expression of ASIC3.

Acid Sensing Ion Channels ; Animals ; Ganglia, Spinal ; metabolism ; Male ; Nerve Tissue Proteins ; metabolism ; Protective Agents ; pharmacology ; Random Allocation ; Rats ; Rats, Wistar ; Restraint, Physical ; adverse effects ; Sodium Channels ; metabolism ; Stomach Diseases ; etiology ; prevention & control ; Stress, Physiological ; Sufentanil ; pharmacology

The experiments were carried out to test whether acid-sensing ion channel 1a and 3 (ASIC1a and ASIC3) were expressed on the primarily cultured type I cells of rat carotid bodies (CBs) and whether the expression of the channels was affected by acid stimulation. The Sprague-Dawley rats of either sex (50-100 g) were used. The CBs were isolated and primarily cultured. The immunofluorescent technique was used to detect the expression of tyrosine hydroxylase (TH), a specific marker of type I cells, in order to identify the type of the cultured cells. The double-label immunofluorescent technique was used to detect the expression of ASIC1a and ASIC3 on the TH-positive type I cells. To detect the influence of acid stimulation on the expressions of ASIC1a and ASIC3, each batch of primarily cultured cells were randomly divided into pH7.3 group (control group), pH6.8 group and pH6.2 group (n=9 in each group). The cells in above three groups were treated with pH7.3, pH6.8 and pH6.2 mediums for 24 h, respectively, and then the mRNA expressions of ASIC1a and ASIC3 in type I cells were detected by semi-quantitative RT-PCR technique. The results showed that more than 93% of the primarily cultured CB cells were TH-positive, indicating that most of the cultured cells were type I cells. Furthermore, all TH-positive cells expressed ASIC1a or ASIC3. After the cells were treated with acid stimulation, the amount of ASIC1a mRNA did not change significantly (P>0.05 vs control group); the amount of ASIC3 mRNA had no significant change in pH6.8 group compared with that in control group, but decreased significantly in pH6.2 group (P<0.01 vs control group, P<0.05 vs pH6.8 group). It is concluded that acid stimulation down-regulates the level of ASIC3 mRNA, but has no effect on the level of ASIC1a mRNA.
Acid Sensing Ion Channels ; metabolism ; Acids ; pharmacology ; Animals ; Carotid Body ; cytology ; metabolism ; Cells, Cultured ; Female ; Male ; Rats ; Rats, Sprague-Dawley