Mammalian homologues of Drosophila melanogaster transient receptor potential (TRP) are a large family of multimeric cation channels that act, or putatively act, as sensors of one or more chemical factor1,2. Major research objectives are the identification of endogenous activators and the determination of cellular and tissue functions of these novel channels. Here we show activation of TRPC5 homomultimeric and TRPC5-TRPC1 heteromultimeric channels3-5 by extracellular reduced thioredoxin acting by breaking a disulphide bridge in the predicted extracellular loop adjacent to the ion-selectivity filter of TRPC5. Thioredoxin is an endogenous redox protein with established intracellular functions, but it is also secreted and its extracellular targets are largely unknown6-9. Particularly high extracellular concentrations of thioredoxin are apparent in rheumatoid arthritis8,10-12, an inflammatory joint disease disabling millions of people worldwide13. We show that TRPC5 and TRPC1 are expressed in secretory fibroblast-like synoviocytes from patients with rheumatoid arthritis, endogenous TRPC5-TRPC1 channels of the cells are activated by reduced thioredoxin, and blockade of the channels enhances secretory activity and prevents suppression of secretion by thioredoxin. The data suggest a novel ion channel activation mechanism that couples extracellular thioredoxin to cell function.Striking activators of TRPC5 are extracellular lanthanide ions4,14,15. Effects of these ions depend on a glutamic acid residue at position 54314 in the predicted extracellular loop adjacent to the ion pore (Supplementary Fig. 1-2). This structural feature may, therefore, have functional importance in enabling extracellular factors to activate the channels. Because lanthanides are unlikely physiological activators we were interested in alternatives and developed a hypothesis based on amino acid sequence alignment which showed two cysteine residues near glutamic acid 543 that are conserved in TRPC5, TRPC4 and TRPC1 ( Supplementary Fig. 2), a subset of the seven TRPC channels1-5. TRPC5 and TRPC4 have similar functional properties4 and both form heteromultimers with TRPC13-5, a subunit that has weak targeting to the plasma membrane when expressed in isolation3,16. Pairs of cysteine residues may be covalently linked by a disulphide bridge that can be cleaved by reduction. We therefore applied the chemical reducing agent dithiothreitol (DTT) to HEK 293 cells expressing TRPC515,16. There was channel activation with the characteristic current-voltage relationship (I-V) of TRPC5 and block by 2-APB, an inhibitor of TRPC55 (Fig. 1a, b, d). Current recovered on wash-out of DTT (data not shown). Similarly, the membrane-impermeable disulphide reducing agent TCEP (Fig. 1c, d) activated TRPC5, whereas the thiol reagent MTSET had no effect (Fig. 1d). TRPC5 was inhibited by cadmium ions only after pre-treatment with DTT ( Fig. 1e, f), consistent with the metal ion acting by re-engaging cysteines17. Other TRP channels lacking the cysteine pair in a similar po...

Objective Mutations in KCNT1 have been implicated in autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and epilepsy of infancy with migrating focal seizures (EIMFS). More recently, a whole exome sequencing study of epileptic encephalopathies identified an additional de novo mutation in one proband with EIMFS. We aim to investigate the electrophysiological and pharmacological characteristics of hKCNT1 mutations and examine developmental expression levels. Methods Here we use a Xenopus laevis oocyte based automated two-electrode voltage-clamp assay. The effects of quinidine (100 and 300 µM) are also tested. Using quantitative RT-PCR, the relative levels of mouse brain mKcnt1 mRNA expression are determined. Results We demonstrate that KCNT1 mutations implicated in epilepsy cause a marked increase in function. Importantly, there was a significant group difference in gain-of-function between mutations associated with ADNFLE and EIMFS. Finally, exposure to quinidine significantly reduces this gain-of-function for all mutations studied. Interpretation These results establish direction for a targeted therapy and potentially exemplify a translational paradigm for in vitro studies informing novel therapies in a neuropsychiatric disease.

The ionotropic ATP receptor subunits P2X(1-6) receptors play important roles in synaptic transmission, yet the P2X(7) receptor has been reported as absent from neurons in the normal adult brain. Here we use RT-PCR to demonstrate that transcripts for the P2X(7) receptor are present in extracts from the medulla oblongata, spinal cord, and nodose ganglion. Using in situ hybridization mRNA encoding, the P2X(7) receptor was detected in numerous neurons throughout the medulla oblongata and spinal cord. Localizing the P2X(7) receptor protein with immunohistochemistry and electron microscopy revealed that it is targeted to presynaptic terminals in the CNS. Anterograde labeling of vagal afferent terminals before immunohistochemistry confirmed the presence of the receptor in excitatory terminals. Pharmacological activation of the receptor in spinal cord slices by addition of 2'- and 3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP; 30 microm) resulted in glutamate mediated excitation of recorded neurons, blocked by P2X(7) receptor antagonists oxidized ATP (100 microm) and Brilliant Blue G (2 microm). At the neuromuscular junction (NMJ) immunohistochemistry revealed that the P2X(7) receptor was present in motor nerve terminals. Furthermore, motor nerve terminals loaded with the vital dye FM1-43 in isolated NMJ preparations destained after application of BzATP (30 microm). This BzATP evoked destaining is blocked by oxidized ATP (100 microm) and Brilliant Blue G (1 microm). This indicates that activation of the P2X(7) receptor promotes release of vesicular contents from presynaptic terminals. Such a widespread distribution and functional role suggests that the receptor may be involved in the fundamental regulation of synaptic transmission at the presynaptic site.

Although originally cloned from rat brain, the P2X 7 receptor has only recently been localized in neurones, and functional responses mediated by these neuronal P2X 7 receptors (P2X 7 R) are largely unknown. Here we studied the effect of P2X 7 R activation on the release of neurotransmitters from superfused rat hippocampal slices. ATP (1-30 mM) and other ATP analogues elicited concentration-dependent

We report 2 patients with drug-resistant epilepsy caused by KCNT1 mutations who were treated with quinidine. Both mutations manifested gain of function in vitro, showing increased current that was reduced by quinidine. One, who had epilepsy of infancy with migrating focal seizures, had 80% reduction in seizure frequency as recorded in seizure diaries, and partially validated by objective seizure evaluation on EEG. The other, who had a novel phenotype, with severe nocturnal focal and secondary generalized seizures starting in early childhood with developmental regression, did not improve. Although quinidine represents an encouraging opportunity for therapeutic benefits, our experience suggests caution in its application and supports the need to identify more targeted drugs for KCNT1 epilepsies.

SignificanceSpider venom is a rich source of peptides, many targeting ion channels. We assessed a venom peptide, Hm1a, as a potential targeted therapy for Dravet syndrome, the genetic epilepsy linked to a mutation in the gene encoding the sodium channel alpha subunit NaV1.1. Cell-based assays showed Hm1a was selective for hNaV1.1 over other sodium and potassium channels. Utilizing a mouse model of Dravet syndrome, Hm1a restored inhibitory neuron function and significantly reduced seizures and mortality in heterozygote mice. Evidence from the structure of Hm1a and modeling suggest Hm1a interacts with NaV1.1 inactivation domains, providing a structural correlate of the functional mechanisms. This proof-of-concept study provides a promising strategy for future drug development in genetic epilepsy and other neurogenetic disorders.

The channels are thought to have structural similarity to ␣-subunits of voltage-gated K ϩ channels, with intracellular amino and carboxy termini and four proteins required for coordination of a single ion pore. As with K ϩ channels, heteromultimerization confers greater diversity. However, unlike voltage-gated K ϩ channels, membrane depolarization is not the primary trigger for channel activity. Instead, chemical factors are considered to be primary stimuli. Details of the chemical sensing properties are becoming apparent and hold promise for revealing further complexity and novelty. In addition, important roles of TRP channels have emerged, including in sensation and cell survival, but we are far from a full appreciation of the purposes of these channels and, in some cases, there is relatively little understanding of TRP family members -one example being TRPM3.

Abstract-Stromal interaction molecule 1 (STIM1) is a predicted single membrane-spanning protein involved in store-operated calcium entry and interacting with ion channels including TRPC1. Here, we focus on endogenous STIM1 of modulated vascular smooth muscle cells, which exhibited a nonselective cationic current in response to store depletion despite strong buffering of intracellular calcium at the physiological concentration. STIM1 mRNA and protein were detected and suppressed by specific short interfering RNA. Calcium entry evoked by store depletion was partially inhibited by STIM1 short interfering RNA, whereas calcium release was unaffected. STIM1 short interfering RNA suppressed cell migration but not proliferation. Antibody that specifically bound STIM1 revealed constitutive extracellular N terminus of STIM1 and extracellular application of the antibody caused fast inhibition of the current evoked by store depletion. The antibody also inhibited calcium entry and cell migration but not proliferation. STIM1 interacted with TRPC1, and TRPC1 contributed partially to calcium entry and cationic current. However, the underlying processes could not be explained only by a STIM1-TRPC1 partnership because extracellular TRPC1 antibody suppressed cationic current only in a fraction of cells, TRPC1-containing channels were important for cell proliferation as well as migration, and cell surface localization studies revealed TRPC1 alone, as well as with STIM1. The data suggest a complex situation in which there is not only plasma membrane-spanning STIM1 that is important for cell migration and TRPC1-independent store-operated cationic current but also TRPC1-STIM1 interaction, a TRPC1-dependent component of store-operated current, and STIM1-independent TRPC1 linked to cell proliferation. (Circ Res. 2008;103:e97-e104.)Key Words: vascular smooth muscle Ⅲ calcium channel Ⅲ stromal interaction molecule 1 Ⅲ transient receptor potential canonical 1 V ascular smooth muscle cells (VSMCs) in their contractile phenotype determine the caliber of most blood vessels and thus regulate blood pressure and local tissue perfusion. Throughout life, however, VSMCs also retain capacity for plasticity, which enables switching to a noncontractile modulated phenotype that is important for blood vessel formation, vascular adaptation, and response to injury, as well as contributing substantially to the vascular diseases of atherosclerosis, neointimal hyperplasia and in-stent restenosis. 1,2 Critical events regulating these VSMC properties are plasma membrane ion fluxes, such as Ca 2ϩ entry through Ca 2ϩ -permeable ion channels. [3][4][5][6][7][8] Voltage-gated Ca 2ϩ channels, especially the dihydropyridine-sensitive L-type channel (Ca V 1.2), have established pharmacological importance and roles in contractile VSMCs. There are, however, other types of Ca 2ϩ -permeable channels that are not voltage-gated and have importance in both VSMC phenotypes. 4 -8 One type is coupled to Ca 2ϩ store depletion: the store-operated channels, which are Ca 2ϩ -and ...