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Background and Purpose: The analgesic action of paracetamol involves K V 7 channels, and its metabolite N-acetyl-p-benzo quinone imine (NAPQI), a cysteine modifying reagent, was shown to increase currents through such channels in nociceptors. Modification of cysteine residues by N-ethylmaleimide, H 2 O 2 , or nitric oxide has been found to modulate currents through K V 7 channels. The study aims to identify whether, and if so which, cysteine residues in neuronal K V 7 channels might be responsible for the effects of NAPQI., Experimental Approach: To address this question, we used a combination of perforated patch-clamp recordings, site-directed mutagenesis, and mass spectrometry applied to recombinant K V 7.1 to K V 7.5 channels., Key Results: Currents through the cardiac subtype K V 7.1 were reduced by NAPQI. Currents through all other subtypes were increased, either by an isolated shift of the channel voltage dependence to more negative values (K V 7.3) or by such a shift combined with increased maximal current levels (K V 7.2, K V 7.4, K V 7.5). A stretch of three cysteine residues in the S2-S3 linker region of K V 7.2 was necessary and sufficient to mediate these effects., Conclusion and Implication: The paracetamol metabolite N-acetyl-p-benzo quinone imine (NAPQI) modifies cysteine residues of K V 7 subunits and reinforces channel gating in homomeric and heteromeric K V 7.2 to K V 7.5, but not in K V 7.1 channels. In K V 7.2, a triple cysteine motif located within the S2-S3 linker region mediates this reinforcement that can be expected to reduce the excitability of nociceptors and to mediate antinociceptive actions of paracetamol., (© 2024 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Background and Purpose: The Kv 7 channel activator flupirtine is a clinical analgesic characterized as 'selective neuronal potassium channel opener'. Flupirtine was found to exert comparable actions at GABAA receptors and Kv 7 channels in neurons of pain pathways, but not in hippocampus., Experimental Approach: Expression patterns of GABAA receptors were explored in immunoblots of rat dorsal root ganglia, dorsal horns and hippocampi using antibodies for 10 different subunits. Effects of flupirtine on recombinant and native GABAA receptors were investigated in patch clamp experiments and compared with the actions on Kv 7 channels., Key Results: Immunoblots pointed towards α2, α3, β3 and γ2 subunits as targets, but in all γ2-containing receptors the effects of flupirtine were alike: leftward shift of GABA concentration-response curves and diminished maximal amplitudes. After replacement of γ2S by δ, flupirtine increased maximal amplitudes. Currents through α1β2δ receptors were more enhanced than those through Kv 7 channels. In hippocampal neurons, flupirtine prolonged inhibitory postsynaptic currents, left miniature inhibitory postsynaptic currents (mIPSCs) unaltered and increased bicuculline-sensitive tonic currents; penicillin abolished mIPSCs, but not tonic currents; concentration-response curves for GABA-induced currents were shifted to the left by flupirtine without changes in maximal amplitudes; in the presence of penicillin, maximal amplitudes were increased; GABA-induced currents in the presence of penicillin were more sensitive towards flupirtine than K(+) currents. In dorsal horn neurons, currents evoked by the δ-preferring agonist THIP (gaboxadol) were more sensitive towards flupirtine than K(+) currents., Conclusions and Implications: Flupirtine prefers δ-containing GABAA receptors over γ-containing ones and over Kv 7 channels., (© 2015 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Background and Purpose: Flupirtine is a non-opioid analgesic that has been in clinical use for more than 20 years. It is characterized as a selective neuronal potassium channel opener (SNEPCO). Nevertheless, its mechanisms of action remain controversial and are the purpose of this study., Experimental Approach: Effects of flupirtine on native and recombinant voltage- and ligand-gated ion channels were explored in patch-clamp experiments using the following experimental systems: recombinant K(IR)3 and K(V)7 channels and α3β4 nicotinic acetylcholine receptors expressed in tsA 201 cells; native voltage-gated Na(+), Ca(2+), inward rectifier K(+), K(V)7 K(+), and TRPV1 channels, as well as GABA(A), glycine, and ionotropic glutamate receptors expressed in rat dorsal root ganglion, dorsal horn and hippocampal neurons., Key Results: Therapeutic flupirtine concentrations (≤10 µM) did not affect voltage-gated Na(+) or Ca(2+) channels, inward rectifier K(+) channels, nicotinic acetylcholine receptors, glycine or ionotropic glutamate receptors. Flupirtine shifted the gating of K(V)7 K(+) channels to more negative potentials and the gating of GABA(A) receptors to lower GABA concentrations. These latter effects were more pronounced in dorsal root ganglion and dorsal horn neurons than in hippocampal neurons. In dorsal root ganglion and dorsal horn neurons, the facilitatory effect of therapeutic flupirtine concentrations on K(V)7 channels and GABA(A) receptors was comparable, whereas in hippocampal neurons the effects on K(V)7 channels were more pronounced., Conclusions and Implications: These results indicate that flupirtine exerts its analgesic action by acting on both GABA(A) receptors and K(V)7 channels., (© 2012 The Authors. British Journal of Pharmacology © 2012 The British Pharmacological Society.)

Background and Purpose: P2Y(1) , P2Y(2) , P2Y(4) , P2Y(12) and P2Y(13) receptors for nucleotides have been reported to mediate presynaptic inhibition, but unequivocal evidence for facilitatory presynaptic P2Y receptors is not available. The search for such receptors was the purpose of this study., Experimental Approach: In primary cultures of rat superior cervical ganglion neurons and in PC12 cell cultures, currents were recorded via the perforated patch clamp technique, and the release of [(3) H]-noradrenaline was determined., Key Results: ADP, 2-methylthio-ATP and ATP enhanced stimulation-evoked (3) H overflow from superior cervical ganglion neurons, treated with pertussis toxin to prevent the signalling of inhibitory G proteins. This effect was abolished by P2Y(1) antagonists and by inhibition of phospholipase C, but not by inhibition of protein kinase C or depletion of intracellular Ca(2+) stores. ADP and a specific P2Y(1) agonist caused inhibition of Kv7 channels, and this was prevented by a respective antagonist. In neurons not treated with pertussis toxin, (3) H overflow was also enhanced by a specific P2Y(1) agonist and by ADP, but only when the P2Y(12) receptors were blocked. ADP also enhanced K(+) -evoked (3) H overflow from PC12 cells treated with pertussis toxin, but only in a clone expressing recombinant P2Y(1) receptors., Conclusions and Implications: These results demonstrate that presynaptic P2Y(1) receptors mediate facilitation of transmitter release from sympathetic neurons most likely through inhibition of Kv7 channels., (© 2011 The Authors. British Journal of Pharmacology © 2011 The British Pharmacological Society.)