Stimulating presynaptic terminals can increase the proton concentration in synapses. Potential receptors for protons are acidsensing ion channels (ASICs), Na + -and Ca 2+ -permeable channels that are activated by extracellular acidosis. Those observations suggest that protons might be a neurotransmitter. We found that presynaptic stimulation transiently reduced extracellular pH in the amygdala. The protons activated ASICs in lateral amygdala pyramidal neurons, generating excitatory postsynaptic currents. Moreover, both protons and ASICs were required for synaptic plasticity in lateral amygdala neurons. The results identify protons as a neurotransmitter, and they establish ASICs as the postsynaptic receptor. They also indicate that protons and ASICs are a neurotransmitter/ receptor pair critical for amygdala-dependent learning and memory.long-term potentiation | PcTX1 | acid sensing ion channel

Rationale: Cardiac fibrosis contributes to pathogenesis of atrial fibrillation (AF), which is the most commonly sustained arrhythmia and a major cause of morbidity and mortality.

Acid-sensing ion channel 1A (ASIC1A) is abundant in the nucleus accumbens (NAc), a region known for its role in addiction. Because ASIC1A has been previously suggested to promote associative learning, we hypothesized that disrupting ASIC1A in the NAc would reduce drug-associated learning and memory. However, contrary to this hypothesis, we found that disrupting ASIC1A in the NAc increased cocaine-conditioned place preference, suggesting an unexpected role for ASIC1A in addiction-related behavior. Moreover, overexpressing ASIC1A in rat NAc reduced cocaine self-administration. Investigating the underlying mechanisms, we identified a novel postsynaptic current during neurotransmission mediated by ASIC1A and ASIC2 and thus well-positioned to regulate synapse structure and function. Consistent with this possibility, disrupting ASIC1A altered dendritic spine density and glutamate receptor function, and increased cocaine-evoked plasticity in AMPA-to-NMDA ratio, all resembling changes previously associated with cocaine-induced behavior. Together, these data suggest ASIC1A inhibits plasticity underlying addiction-related behavior, and raise the possibility of therapies for drug addiction by targeting ASIC-dependent neurotransmission.

The channel kinases TRPM6 and TRPM7 have recently been discovered to play important roles in Mg 2؉ and Ca 2؉ homeostasis, which is critical to both human health and cell viability. However, the molecular basis underlying these channels' unique Mg 2؉ and Ca 2؉ permeability and pH sensitivity remains unknown. Here we have created a series of amino acid substitutions in the putative pore of TRPM7 to evaluate the origin of the permeability of the channel and its regulation by pH. Two mutants of TRPM7, E1047Q and E1052Q, produced dramatic changes in channel properties. The I-V relations of E1052Q and E1047Q were significantly different from WT TRPM7, with the inward currents of 8-and 12-fold larger than TRPM7, respectively. permeation, rendering TRPM7 a monovalent selective channel. In addition, the ability of protons to potentiate inward currents was lost in E1047Q, indicating that E1047 is critical to Ca 2؉ and Mg 2؉ permeability of TRPM7, and its pH sensitivity. Mutation of the corresponding residues in the pore of TRPM6, E1024Q and E1029Q, produced nearly identical changes to the channel properties of TRPM6. Our results indicate that these two glutamates are key determinants of both channels' divalent selectivity and pH sensitivity. These findings reveal the molecular mechanisms underpinning physiological/pathological functions of TRPM6 and TRPM7, and will extend our understanding of the pore structures of TRPM channels.TRPM6 and TRPM7 belong to the TRP channel superfamily (1-5) and are distinguished from other known ion channels by virtue of having both ion channel and protein kinase activities (6 -11). In addition, TRPM6 and TRPM7 uniquely exhibit strong outward rectification, permeation to Ca 2ϩ , Mg 2ϩ , monovalent cations, and a wide array of trace metals (6 -8, 11, 12 (8,20,21,23), whereas TRPM7 is ubiquitously expressed, with highest expression in the kidney and heart (5, 6). In addition to these channels' regulation of Mg 2ϩ homeostasis, several studies have suggested multiple cellular and physiology functions for TRPM7, including anoxic neuronal death (24), cell adhesion and actomyosin contractility (25, 26), and skeletogenesis (27). Although the mechanisms by which TRPM6 and TRPM7 exert their physiological and/or pathological functions are not yet completely understood, it is clear that permeation of Ca 2ϩ and Mg 2ϩ contributes substantially to the known functions of these channels (7, 20 -22, 24, 25, 27). Moreover, a recent study demonstrated that the sensitivity of TRPM7 to external pH may contribute to controlling neurotransmitter release (28). Therefore, it is essential to understand the molecular mechanisms underlying the Ca 2ϩ and Mg 2ϩ permeability of TRPM6 and TRPM7, as well as their sensitivities to changes in pH.The aim of the present study was to identify the amino acid residues that determine Mg 2ϩ and Ca 2ϩ permeation of TRPM6 and TRPM7. We previously demonstrated that external protons significantly enhance TRPM6 and TRPM7 inward currents (11,19) by decreasing the divalent affinity to t...

The transient receptor potential (TRP) superfamily consists of a large number of nonselective cation channels with variable degree of Ca(2+)-permeability. The 28 mammalian TRP channel proteins can be grouped into six subfamilies: canonical, vanilloid, melastatin, ankyrin, polycystic, and mucolipin TRPs. The majority of these TRP channels are expressed in different cell types including both excitable and nonexcitable cells of the cardiovascular system. Unlike voltage-gated ion channels, TRP channels do not have a typical voltage sensor, but instead can sense a variety of other stimuli including pressure, shear stress, mechanical stretch, oxidative stress, lipid environment alterations, hypertrophic signals, and inflammation products. By integrating multiple stimuli and transducing their activity to downstream cellular signal pathways via Ca(2+) entry and/or membrane depolarization, TRP channels play an essential role in regulating fundamental cell functions such as contraction, relaxation, proliferation, differentiation, and cell death. With the use of targeted deletion and transgenic mouse models, recent studies have revealed that TRP channels are involved in numerous cellular functions and play an important role in the pathophysiology of many diseases in the cardiovascular system. Moreover, several TRP channels are involved in inherited diseases of the cardiovascular system. This review presents an overview of current knowledge concerning the physiological functions of TRP channels in the cardiovascular system and their contributions to cardiovascular diseases. Ultimately, TRP channels may become potential therapeutic targets for cardiovascular diseases.

Background TRPC6, encoding a member of the transient receptor potential (TRP) superfamily of ion channels, is a calcium-permeable cation channel, which mediates capacitive calcium entry into the cell. Until today, seven different mutations in TRPC6 have been identified as a cause of autosomal-dominant focal segmental glomerulosclerosis (FSGS) in adults.Methodology/Principal FindingsHere we report a novel TRPC6 mutation that leads to early onset FSGS. We identified one family in whom disease segregated with a novel TRPC6 mutation (M132T), that also affected pediatric individuals as early as nine years of age. Twenty-one pedigrees compatible with an autosomal-dominant mode of inheritance and biopsy-proven FSGS were selected from a worldwide cohort of 550 families with steroid resistant nephrotic syndrome (SRNS). Whole cell current recordings of the mutant TRPC6 channel, compared to the wild-type channel, showed a 3 to 5-fold increase in the average out- and inward TRPC6 current amplitude. The mean inward calcium current of M132T was 10-fold larger than that of wild-type TRPC6. Interestingly, M132T mutants also lacked time-dependent inactivation. Generation of a novel double mutant M132T/N143S did not further augment TRPC6 channel activity.ConclusionsIn summary, our data shows that TRPC6 mediated FSGS can also be found in children. The large increase in channel currents and impaired channel inactivation caused by the M132T mutant leads to an aggressive phenotype that underlines the importance of calcium dose channeled through TRPC6.

Melastatin-related transient receptor potential channel 2 (TRPM2) is a Ca 2؉ -permeable, nonselective cation channel that is involved in oxidative stress-induced cell death and inflammation processes. Although TRPM2 can be activated by ADP-ribose (ADPR) in vitro, it was unknown how TRPM2 is gated in vivo. Moreover, several alternative spliced isoforms of TRPM2 identified recently are insensitive to ADPR, and their gating mechanisms remain unclear. Here, we report that intracellular Ca 2؉ ( Ca 2ϩ signaling ͉ gating mechanism ͉ ADP-ribose ͉ calmodulin-binding domain ͉ oxidative stress T ransient receptor potential (TRP) channels have been shown to play important roles under physiological and pathological conditions (1-3). TRPM2, also referred to as TRPC7 (4) or LTRPC2 (5-7), is a member of the melastatin-related (TRPM) TRP channel subfamily, which possesses both ion-channel and ADP-ribose (ADPR) hydrolase functions (5-7). TRPM2 is a Ca 2ϩ -permeable, nonselective cation channel that is predominantly expressed in various regions of the brain and is also expressed in other tissues, including spleen, heart, liver, lung, and bone marrow (4-6). Studies at cellular levels have implicated that TRPM2 is involved in oxidative stress-mediated cortical and striatal neuronal cell death (8, 9), hematopoietic cell death (5, 8, 10), and insulin secretion (11). A recent report demonstrated that TRPM2 regulates reactive oxygen species-induced chemokine production in monocytes, thereby aggravating inflammation (12).TRPM2 has been shown to be activated by ADPR (6, 7), oxidative stress (5, 13, 14), NAD ϩ (5, 7, 15), cADPR, and nicotinic acid adenine dinucleotide phosphate (NAADP) (16,17 (6, 22). An increase in [Ca 2ϩ ] i level significantly reduces the ADPR concentration required for TRPM2 activation (6). External Ca 2ϩ also has been shown to influence ADPR-mediated TRPM2 gating (22, 23). However, the detailed mechanisms by which Ca 2ϩ synergizes with ADPR in activating TRPM2 remain unknown.Whereas the gating mechanism and physiological functions of the full-length TRPM2 have been studied extensively, information pertaining to TRPM2 alternative spliced isoforms is largely unavailable (24). Several splice variants of TRPM2 have been identified, including a shorter form (SSF-TRPM2) in which the Nterminal 214-aa residues are removed (25), a C-terminal truncation (TRPM2-⌬C) lacking exon 27, and an N-terminal truncation (TRPM2-⌬N) lacking a portion of exon 11 (13,15). Although the full-length TRPM2 can be activated by ADPR, NAD ϩ , and H 2 O 2 , it appears that the spliced isoforms cannot be activated by the known activators for the full-length TRPM2 (18,24,26). Therefore, it was unclear whether the spliced isoforms can form functional channels (18,24,26). Insufficient knowledge about the gating mechanism of the alternative spliced isoforms of TRPM2 largely hampered the investigation of their physiological and/or pathological functions.A better understanding of TRPM2 gating mechanism as well as how TRPM2 alternative spliced isoforms can ...

TRPM2 is a Ca2+-permeable nonselective cation channel that plays important roles in oxidative stress–mediated cell death and inflammation processes. However, how TRPM2 is regulated under physiological and pathological conditions is not fully understood. Here, we report that both intracellular and extracellular protons block TRPM2 by inhibiting channel gating. We demonstrate that external protons block TRPM2 with an IC50 of pHo = 5.3, whereas internal protons inhibit TRPM2 with an IC50 of pHi = 6.7. Extracellular protons inhibit TRPM2 by decreasing single-channel conductance. We identify three titratable residues, H958, D964, and E994, at the outer vestibule of the channel pore that are responsible for pHo sensitivity. Mutations of these residues reduce single-channel conductance, decrease external Ca2+ ([Ca2+]o) affinity, and inhibit [Ca2+]o-mediated TRPM2 gating. These results support the following model: titration of H958, D964, and E994 by external protons inhibits TRPM2 gating by causing conformation change of the channel, and/or by decreasing local Ca2+ concentration at the outer vestibule, therefore reducing [Ca2+]o permeation and inhibiting [Ca2+]o-mediated TRPM2 gating. We find that intracellular protons inhibit TRPM2 by inducing channel closure without changing channel conductance. We identify that D933 located at the C terminus of the S4-S5 linker is responsible for intracellular pH sensitivity. Replacement of Asp933 by Asn933 changes the IC50 from pHi = 6.7 to pHi = 5.5. Moreover, substitution of Asp933 with various residues produces marked changes in proton sensitivity, intracellular ADP ribose/Ca2+ sensitivity, and gating profiles of TRPM2. These results indicate that D933 is not only essential for intracellular pH sensitivity, but it is also crucial for TRPM2 channel gating. Collectively, our findings provide a novel mechanism for TRPM2 modulation as well as molecular determinants for pH regulation of TRPM2. Inhibition of TRPM2 by acidic pH may represent an endogenous mechanism governing TRPM2 gating and its physiological/pathological functions.