101
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Elmedyb P, Calloe K, Schmitt N, Hansen RS, Grunnet M, Olesen SP. Modulation of ERG Channels by XE991. Basic Clin Pharmacol Toxicol 2007; 100:316-22. [PMID: 17448117 DOI: 10.1111/j.1742-7843.2007.00048.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In neuronal tissue, KCNQ2-5 channels conduct the physiologically important M-current. In some neurones, the M-current may in addition be conducted partly by ERG potassium channels, which have widely overlapping expression with the KCNQ channel subunits. XE991 and linopiridine are known to be standard KCNQ potassium channel blockers. These compounds have been used in many different tissues as specific pharmacological tools to discern native currents conducted by KCNQ channels from other potassium currents. In this article, we demonstrate that ERG1-2 channels are also reversibly inhibited by XE991 in the micromolar range (EC(50) 107 microM for ERG1). The effect has been characterized in Xenopus laevis oocytes expressing ERG1-2 and in the mammalian HEK293 cell line stably expressing ERG1 channels. The IC(50) values for block of KCNQ channels by XE991 range 1-65 microM. In conclusion, great care should be taken when choosing the concentration of XE991 to use for experiments on native potassium channels or animal studies in order to be able to conclude on selective KCNQ channel-mediated effects.
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Affiliation(s)
- Pernille Elmedyb
- Department of Medical Physiology, The Panum Institute, The University of Copenhagen, Denmark
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102
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Xiong Q, Sun H, Li M. Zinc pyrithione-mediated activation of voltage-gated KCNQ potassium channels rescues epileptogenic mutants. Nat Chem Biol 2007; 3:287-96. [PMID: 17435769 DOI: 10.1038/nchembio874] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Accepted: 03/20/2007] [Indexed: 11/09/2022]
Abstract
KCNQ potassium channels are activated by changes in transmembrane voltage and play an important role in controlling electrical excitability. Human mutations of KCNQ2 and KCNQ3 potassium channel genes result in reduction or loss of channel activity and cause benign familial neonatal convulsions (BFNCs). Thus, small molecules capable of augmenting KCNQ currents are essential both for understanding the mechanism of channel activity and for developing therapeutics. We performed a high-throughput screen in search for agonistic compounds potentiating KCNQ potassium channels. Here we report identification of a new opener, zinc pyrithione (1), which activates both recombinant and native KCNQ M currents. Interactions with the channel protein cause an increase of single-channel open probability that could fully account for the overall conductance increase. Separate point mutations have been identified that either shift the concentration dependence or affect potentiation efficacy, thereby providing evidence for residues influencing ligand binding and downstream events. Furthermore, zinc pyrithione is capable of rescuing the mutant channels causal to BFNCs.
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Affiliation(s)
- Qiaojie Xiong
- Department of Neuroscience, High Throughput Biology Center, School of Medicine, Johns Hopkins University, 733 North Broadway, Baltimore, Maryland 21205, USA
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103
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Jensen HS, Grunnet M, Olesen SP. Inactivation as a new regulatory mechanism for neuronal Kv7 channels. Biophys J 2007; 92:2747-56. [PMID: 17237198 PMCID: PMC1831682 DOI: 10.1529/biophysj.106.101287] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated K(+) channels of the Kv7 (KCNQ) family have important physiological functions in both excitable and nonexcitable tissue. The family encompasses five genes encoding the channel subunits Kv7.1-5. Kv7.1 is found in epithelial and cardiac tissue. Kv7.2-5 channels are predominantly neuronal channels and are important for controlling excitability. Kv7.1 channels have been considered the only Kv7 channels to undergo inactivation upon depolarization. However, here we demonstrate that inactivation is also an intrinsic property of Kv7.4 and Kv7.5 channels, which inactivate to a larger extent than Kv7.1 channels at all potentials. We demonstrate that at least 30% of these channels are inactivated at physiologically relevant potentials. The onset of inactivation is voltage dependent and occurs on the order of seconds. Both time- and voltage-dependent recovery from inactivation was investigated for Kv7.4 channels. A time constant of 1.47 +/- 0.21 s and a voltage constant of 54.9 +/- 3.4 mV were determined. It was further demonstrated that heteromeric Kv7.3/Kv7.4 channels had inactivation properties different from homomeric Kv7.4 channels. Finally, the Kv7 channel activator BMS-204352 was in contrast to retigabine found to abolish inactivation of Kv7.4. In conclusion, this work demonstrates that inactivation is a key regulatory mechanism of Kv7.4 and Kv7.5 channels.
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Affiliation(s)
- Henrik Sindal Jensen
- The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Medical Physiology, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark.
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104
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Kullmann PHM, Horn JP. Excitatory muscarinic modulation strengthens virtual nicotinic synapses on sympathetic neurons and thereby enhances synaptic gain. J Neurophysiol 2006; 96:3104-13. [PMID: 17005615 PMCID: PMC1839880 DOI: 10.1152/jn.00589.2006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acetylcholine excites many neuronal types by binding to postsynaptic m1-muscarinic receptors that signal to ion channels through the G(q/11) protein. To investigate the functional significance of this metabotropic pathway in sympathetic ganglia, we studied how muscarinic excitation modulated the integration of virtual nicotinic excitatory postsynaptic potentials (EPSPs) created in dissociated bullfrog B-type sympathetic neurons with the dynamic-clamp technique. Muscarine (1 muM) strengthened the impact of virtual synapses by reducing the artificial nicotinic conductance required to reach the postsynaptic firing threshold from 20.9 +/- 5.4 to 13.1 +/- 3.1 nS. Consequently, postganglionic action potential output increased by 4-215% when driven by different patterns of virtual presynaptic activity that were chosen to reflect the range of physiological firing rates and convergence levels seen in amphibian and mammalian sympathetic ganglia. In addition to inhibiting the M-type K(+) conductance, muscarine activated a leak conductance in three of 37 cells. When this leak conductance was reproduced with the dynamic clamp, it also acted to strengthen virtual nicotinic synapses and enhance postganglionic spike output. Combining pharmacological M-conductance suppression with virtual leak activation, at resting potentials between -50 and -55 mV, produced synergistic strengthening of nicotinic synapses and an increase in the integrated postganglionic spike output. Together, these results reveal how muscarinic activation of a branched metabotropic pathway can enhance integration of fast EPSPs by modulating their effective strength. The results also support the hypothesis that muscarinic synapses permit faster and more accurate feedback control of autonomic behaviors by generating gain through synaptic amplification in sympathetic ganglia.
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Affiliation(s)
- Paul H M Kullmann
- Department of Neurobiology, University of Pittsburgh School of Medicine, E 1440 Biomedical Science Tower, Pittsburgh, PA 15261, USA.
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105
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Koyama S, Brodie MS, Appel SB. Ethanol inhibition of m-current and ethanol-induced direct excitation of ventral tegmental area dopamine neurons. J Neurophysiol 2006; 97:1977-85. [PMID: 16956995 PMCID: PMC2372163 DOI: 10.1152/jn.00270.2006] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ethanol-induced excitation of ventral tegmental area dopamine (DA VTA) neurons is thought to be critical for the reinforcing effects of ethanol. Although ligand-gated ion channels are known to be the targets of ethanol, ethanol modulation of voltage-dependent ion channels of central neurons has not been well studied. We have demonstrated that ethanol excites DA VTA neurons by the reduction of sustained K(+) currents and recently reported that M-current (I(M)) regulates action potential generation through fast and slow afterhyperpolarization phases. In the present study we thus examined whether ethanol inhibition of I(M) contributes to the excitation of DA VTA neurons using nystatin-perforated patch current- and voltage-clamp recordings. Ethanol (20-120 mM) reduced I(M) in a concentration-dependent manner and increased the spontaneous firing frequency of DA VTA neurons. Ethanol-induced increase in spontaneous firing frequency correlated positively with ethanol inhibition of I(M) with a slope value of 1.3. Specific I(M) inhibition by XE991 (0.3-10 microM) increased spontaneous firing frequency which correlated positively with I(M) inhibition with a slope value of 0.5. In the presence of 10 muM XE991, a concentration that produced maximal inhibition of I(M), ethanol still increased the spontaneous firing frequency of DA VTA neurons in a concentration-dependent manner. Thus we conclude that, although ethanol causes inhibition of I(M) and this results in some increase in the firing frequency of DA VTA neurons, another effect of ethanol is primarily responsible for the ethanol-induced increase in firing rate in these neurons.
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Affiliation(s)
- Susumu Koyama
- Department of Physiology and Biophysics (M/C 901 University of Illinois at Chicago, 835 S. Wolcott Avenue, Chicago, IL 60612-7342, USA
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106
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Zaika O, Lara LS, Gamper N, Hilgemann DW, Jaffe DB, Shapiro MS. Angiotensin II regulates neuronal excitability via phosphatidylinositol 4,5-bisphosphate-dependent modulation of Kv7 (M-type) K+ channels. J Physiol 2006; 575:49-67. [PMID: 16777936 PMCID: PMC1819424 DOI: 10.1113/jphysiol.2006.114074] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Voltage-gated Kv7 (KCNQ) channels underlie important K+ currents in many different types of cells, including the neuronal M current, which is thought to be modulated by muscarinic stimulation via depletion of membrane phosphatidylinositol 4,5-bisphosphate (PIP2). We studied the role of modulation by angiotensin II (angioII) of M current in controlling discharge properties of superior cervical ganglion (SCG) sympathetic neurons and the mechanism of action of angioII on cloned Kv7 channels in a heterologous expression system. In SCG neurons, which endogenously express angioII AT1 receptors, application of angioII for 2 min produced an increase in neuronal excitability and a decrease in spike-frequency adaptation that partially returned to control values after 10 min of angioII exposure. The increase in excitability could be simulated in a computational model by varying only the amount of M current. Using Chinese hamster ovary (CHO) cells expressing cloned Kv7.2 + 7.3 heteromultimers and AT1 receptors studied under perforated patch clamp, angioII induced a strong suppression of the Kv7.2/7.3 current that returned to near baseline within 10 min of stimulation. The suppression was blocked by the phospholipase C inhibitor edelfosine. Under whole-cell clamp, angioII moderately suppressed the Kv7.2/7.3 current whether or not intracellular Ca2+ was clamped or Ca2+ stores depleted. Co-expression of PI(4)5-kinase in these cells sharply reduced angioII inhibition, but did not augment current amplitudes, whereas co-expression of a PIP2 5'-phosphatase sharply reduced current amplitudes, and also blunted the inhibition. The rebound of the current seen in perforated-patch recordings was blocked by the PI4-kinase inhibitor, wortmannin (50 microM), suggesting that PIP2 re-synthesis is required for current recovery. High-performance liquid chromatographic analysis of anionic phospholipids in CHO cells stably expressing AT1 receptors revealed that PIP2 and phosphatidylinositol 4-phosphate levels are to be strongly depleted after 2 min of stimulation with angioII, with a partial rebound after 10 min. The results of this study establish how angioII modulates M channels, which in turn affects the integrative properties of SCG neurons.
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Affiliation(s)
- Oleg Zaika
- Department of Physiology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA
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107
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Wladyka CL, Kunze DL. KCNQ/M-currents contribute to the resting membrane potential in rat visceral sensory neurons. J Physiol 2006; 575:175-89. [PMID: 16777937 PMCID: PMC1819429 DOI: 10.1113/jphysiol.2006.113308] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The M-current is a slowly activating, non-inactivating potassium current that has been shown to be present in numerous cell types. In this study, KCNQ2, Q3 and Q5, the molecular correlates of M-current in neurons, were identified in the visceral sensory neurons of the nodose ganglia from rats through immunocytochemical studies. All neurons showed expression of each of the three proteins. In voltage clamp studies, the cognition-enhancing drug linopirdine (1-50 microM) and its analogue, XE991 (10 microM), quickly and irreversibly blocked a small, slowly activating current that had kinetic properties similar to KCNQ/M-currents. This current activated between -60 and -55 mV, had a voltage-dependent activation time constant of 208 +/- 12 ms at -20 mV, a deactivation time constant of 165 +/- 24 ms at -50 mV and V1/2 of -24 +/- 2 mV, values which are consistent with previous reports for endogenous M-currents. In current clamp studies, these drugs also led to a depolarization of the resting membrane potential at values as negative as -60 mV. Flupirtine (10-20 microM), an M-current activator, caused a 3-14 mV leftward shift in the current-voltage relationship and also led to a hyperpolarization of resting membrane potential. These data indicate that the M-current is present in nodose neurons, is activated at resting membrane potential and that it is physiologically important in regulating excitability by maintaining cells at negative voltages.
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Affiliation(s)
- Cynthia L Wladyka
- Rammelkamp Centre for Research and Education R326 MetroHealth Medical Centre, 2500 MetroHealth Drive, Cleveland, OH 44109-1998, USA
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108
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Koyama S, Appel SB. Characterization of M-current in ventral tegmental area dopamine neurons. J Neurophysiol 2006; 96:535-43. [PMID: 16394077 DOI: 10.1152/jn.00574.2005] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
M-current (I(M)) is a voltage-gated potassium current (KCNQ type) that affects neuronal excitability and is modulated by some drugs of abuse. Ventral tegmental area (VTA) dopamine (DA) neurons are important for the reinforcing effects of drugs of abuse. Therefore we studied I(M) in acutely dissociated rat DA VTA neurons with nystatin-perforated patch recording. The standard deactivation protocol was used to measure I(M) during voltage-clamp recording with hyperpolarizing voltage steps to -65 mV (in 10-mV increments) from a holding potential of -25 mV. I(M) amplitude was voltage dependent and maximal current amplitude was detected at -45 mV. The deactivation time constant of I(M) was voltage dependent and became shorter at more negative voltages. The I(M)/KCNQ antagonist XE991 (0.3-30 microM) caused a concentration-dependent reduction in I(M) amplitude with an IC(50) of 0.71 microM. Tetraethylammonium (TEA, 0.3-10 mM) caused a concentration-dependent inhibition of I(M) with an IC(50) of 1.56 mM. In current-clamp recordings, all DA VTA neurons were spontaneously active. Analysis of evoked action potential shape indicated that XE991 (1-10 microM) reduced the fast and slow components of the spike afterhyperpolarization (AHP) without affecting the middle component of the AHP. Action potential amplitude, duration, and threshold were not affected by XE991. In addition, 10 microM XE991 significantly shortened the interspike intervals in evoked spike trains. In conclusion, I(M) is active near threshold in DA VTA neurons, is blocked by XE991 (10 microM) and TEA (10 mM), may contribute to the shape of the AHP, and may decrease excitability of these neurons.
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Affiliation(s)
- Susumu Koyama
- Department of Physiology and Biophysics, University of Illinois at Chicago, College of Medicine, Chicago, Illinois 60612-7342, USA
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109
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Abstract
K(+) channels play a crucial role in regulating the excitability of neurons. Many K(+) channels are, in turn, regulated by neurotransmitters. One of the first neurotransmitter-regulated channels to be identified, some 25 years ago, was the M channel. This was categorized as such because its activity was inhibited through stimulation of muscarinic acetylcholine receptors. M channels are now known to be composed of subunits of the Kv7 (KCNQ) K(+) channel family. However, until recently, the link between the receptors and the channels has remained elusive. Here, we summarize recent developments that have begun to clarify this link and discuss their implications for physiology and medicine.
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Affiliation(s)
- Patrick Delmas
- Laboratoire de Neurophysiologie Cellulaire, UMR 6150 CNRS, Faculté de Médecine, IFR Jean Roche, Bd. Pierre Dramard, 13916 Marseille Cedex 20, France.
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110
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Nakajo K, Kubo Y. Protein kinase C shifts the voltage dependence of KCNQ/M channels expressed in Xenopus oocytes. J Physiol 2005; 569:59-74. [PMID: 16179364 PMCID: PMC1464213 DOI: 10.1113/jphysiol.2005.094995] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
It is well established that stimulation of G(q)-coupled receptors such as the M1 muscarinic acetylcholine receptor inhibits KCNQ/M currents. While it is generally accepted that this muscarinic inhibition is mainly caused by the breakdown of PIP(2), the role of the subsequent activation of protein kinase C (PKC) is not well understood. By reconstituting M currents in Xenopus oocytes, we observed that stimulation of coexpressed M1 receptors with 10 microm oxotremorine M (oxo-M) induces a positive shift (4-30 mV, depending on which KCNQ channels are expressed) in the conductance-voltage relationship (G-V) of KCNQ channels. When we applied phorbol 12-myristate 13-acetate (PMA), a potent PKC activator, we observed a large positive shift (17.8 +/- 1.6 mV) in the G-V curve for KCNQ2, while chelerythrine, a PKC inhibitor, attenuated the shift caused by the stimulation of M1 receptors. By contrast, reducing PIP(2) had little effect on the G-V curve for KCNQ2 channels; although pretreating cells with 10 mum wortmannin for 30 min reduced KCNQ2 current amplitude by 80%, the G-V curve was shifted only slightly (5 mV). Apparently, the shift induced by muscarinic stimulation in Xenopus oocytes was mainly caused by PKC activation. When KCNQ2/3 channels were expressed in HEK 293T cells, the G-V curve seemed already to be shifted in a positive direction, even before activation of PKC, and PMA failed to shift the curve any further. That alkaline phosphatase in the patch pipette shifted the G-V curve in a negative direction suggests KCNQ2/3 channels are constitutively phosphorylated in HEK 293T cells.
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Affiliation(s)
- Koichi Nakajo
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi, Japan.
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111
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Horowitz LF, Hirdes W, Suh BC, Hilgemann DW, Mackie K, Hille B. Phospholipase C in living cells: activation, inhibition, Ca2+ requirement, and regulation of M current. J Gen Physiol 2005; 126:243-62. [PMID: 16129772 PMCID: PMC2266577 DOI: 10.1085/jgp.200509309] [Citation(s) in RCA: 250] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2005] [Accepted: 07/19/2005] [Indexed: 01/22/2023] Open
Abstract
We have further tested the hypothesis that receptor-mediated modulation of KCNQ channels involves depletion of phosphatidylinositol 4,5-bisphosphate (PIP2) by phosphoinositide-specific phospholipase C (PLC). We used four parallel assays to characterize the agonist-induced PLC response of cells (tsA or CHO cells) expressing M1 muscarinic receptors: translocation of two fluorescent probes for membrane lipids, release of calcium from intracellular stores, and chemical measurement of acidic lipids. Occupation of M1 receptors activates PLC and consumes cellular PIP2 in less than a minute and also partially depletes mono- and unphosphorylated phosphoinositides. KCNQ current is simultaneously suppressed. Two inhibitors of PLC, U73122 and edelfosine (ET-18-OCH3), can block the muscarinic actions completely, including suppression of KCNQ current. However, U73122 also had many side effects that were attributable to alkylation of various proteins. These were mimicked or occluded by prior reaction with the alkylating agent N-ethylmaleimide and included block of pertussis toxin-sensitive G proteins and effects that resembled a weak activation of PLC or an inhibition of lipid kinases. By our functional criteria, the putative PLC activator m-3M3FBS did stimulate PLC, but with a delay and an irregular time course. It also suppressed KCNQ current. The M1 receptor-mediated activation of PLC and suppression of KCNQ current were stopped by lowering intracellular calcium well below resting levels and were slowed by not allowing intracellular calcium to rise in response to PLC activation. Thus calcium release induced by PLC activation feeds back immediately on PLC, accelerating it during muscarinic stimulation in strong positive feedback. These experiments clarify important properties of receptor-coupled PLC responses and their inhibition in the context of the living cell. In each test, the suppression of KCNQ current closely paralleled the expected fall of PIP2. The results are described by a kinetic model.
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Affiliation(s)
- Lisa F Horowitz
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle 98195, USA
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112
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Berg RW, Friedman B, Schroeder LF, Kleinfeld D. Activation of Nucleus Basalis Facilitates Cortical Control of a Brain Stem Motor Program. J Neurophysiol 2005; 94:699-711. [PMID: 15728764 DOI: 10.1152/jn.01125.2004] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
We tested the hypothesis that activation of nucleus basalis magnocellularis (NBM), which provides cholinergic input to cortex, facilitates motor control. Our measures of facilitation were changes in the direction and time-course of vibrissa movements that are elicited by microstimulation of vibrissa motor (M1) cortex. In particular, microstimulation led solely to a transient retraction of the vibrissae in the sessile animal but to a full motion sequence of protraction followed by retraction in the aroused animal. We observed that activation of NBM, as assayed by cortical desynchronization, induced a transition from microstimulation-evoked retraction to full sweep sequences. This dramatic change in the vibrissa response to microstimulation was blocked by systemic delivery of atropine and, in anesthetized animals, an analogous change was blocked by the topical administration of atropine to M1 cortex. We conclude that NBM significantly facilitates the ability of M1 cortex to control movements. Our results bear on the importance of cholinergic activation in schemes for neuroprosthetic control of movement.
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Affiliation(s)
- Rune W Berg
- Department of Physics 0374, University of California at San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA
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113
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Gamper N, Li Y, Shapiro MS. Structural requirements for differential sensitivity of KCNQ K+ channels to modulation by Ca2+/calmodulin. Mol Biol Cell 2005; 16:3538-51. [PMID: 15901836 PMCID: PMC1182296 DOI: 10.1091/mbc.e04-09-0849] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Calmodulin modulation of ion channels has emerged as a prominent theme in biology. The sensitivity of KCNQ1-5 K+ channels to modulation by Ca2+/calmodulin (CaM) was studied using patch-clamp, Ca2+ imaging, and biochemical and pharmacological approaches. Coexpression of CaM in Chinese hamster ovary (CHO) cells strongly reduced currents of KCNQ2, KCNQ4, and KCNQ5, but not KCNQ1 or KCNQ3. In simultaneous current recording/Ca2+ imaging experiments, CaM conferred Ca2+ sensitivity to KCNQ4 and KCNQ5, but not to KCNQ1, KCNQ3, or KCNQ1/KCNE1 channels. A chimera constructed from the carboxy terminus of KCNQ4 and the rest KCNQ1 displayed Ca2+ sensitivity similar to KCNQ4. Chimeras constructed from different lengths of the KCNQ4 carboxy terminal and the rest KCNQ3 localized a region that confers sensitivity to Ca2+/CaM. Lobe-specific mutations of CaM revealed that its amino-terminal lobe mediates the Ca2+ sensitivity of the KCNQ/CaM complex. The site of CaM action within the channel carboxy terminus overlaps with that of the KCNQ opener N-ethylmaleimide (NEM). We found that CaM overexpression reduced NEM augmentation of KCNQ2, KCNQ4, and KCNQ5, and NEM pretreatment reduced Ca2+/CaM-mediated suppression of M current in sympathetic neurons by bradykinin. We propose that two functionally distinct types of carboxy termini underlie the observed differences among this channel family.
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Affiliation(s)
- Nikita Gamper
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
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114
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Gamper N, Stockand JD, Shapiro MS. The use of Chinese hamster ovary (CHO) cells in the study of ion channels. J Pharmacol Toxicol Methods 2005; 51:177-85. [PMID: 15862463 DOI: 10.1016/j.vascn.2004.08.008] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/25/2004] [Indexed: 11/27/2022]
Abstract
The line of epithelial-like Chinese hamster ovary (CHO) cells was initiated by T.T. Puck in 1957. Since then, CHO cells have become a widely used mammalian expression system in industry and science. This paper discusses the different features of CHO cell physiology as well as the specific aspects of using these cells for ion channel studies; among the discussed features are the culturing and transfection of CHO cells, details of electrophysiological recordings from them and applications for the study of ion channel physiology and pharmacology. Examples of successful reconstitution of mammalian ion channels in CHO cells discussed in the paper include reconstitution of KCNQ channel regulation by muscarinic acetylcholine receptors and the study of the amiloride-sensitivity of epithelial sodium channels (ENaC).
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Affiliation(s)
- Nikita Gamper
- Department of Physiology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio TX 78229, USA
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115
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Affiliation(s)
- Mark S Shapiro
- Department of Physiology, University of Texas Health Science Center at San Antonio, TX 78229, USA
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116
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Suh BC, Horowitz LF, Hirdes W, Mackie K, Hille B. Regulation of KCNQ2/KCNQ3 current by G protein cycling: the kinetics of receptor-mediated signaling by Gq. ACTA ACUST UNITED AC 2005; 123:663-83. [PMID: 15173220 PMCID: PMC2234571 DOI: 10.1085/jgp.200409029] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Receptor-mediated modulation of KCNQ channels regulates neuronal excitability. This study concerns the kinetics and mechanism of M1 muscarinic receptor–mediated regulation of the cloned neuronal M channel, KCNQ2/KCNQ3 (Kv7.2/Kv7.3). Receptors, channels, various mutated G-protein subunits, and an optical probe for phosphatidylinositol 4,5-bisphosphate (PIP2) were coexpressed by transfection in tsA-201 cells, and the cells were studied by whole-cell patch clamp and by confocal microscopy. Constitutively active forms of Gαq and Gα11, but not Gα13, caused a loss of the plasma membrane PIP2 and a total tonic inhibition of the KCNQ current. There were no further changes upon addition of the muscarinic agonist oxotremorine-M (oxo-M). Expression of the regulator of G-protein signaling, RGS2, blocked PIP2 hydrolysis and current suppression by muscarinic stimulation, confirming that the Gq family of G-proteins is necessary. Dialysis with the competitive inhibitor GDPβS (1 mM) lengthened the time constant of inhibition sixfold, decreased the suppression of current, and decreased agonist sensitivity. Removal of intracellular Mg2+ slowed both the development and the recovery from muscarinic suppression. When combined with GDPβS, low intracellular Mg2+ nearly eliminated muscarinic inhibition. With nonhydrolyzable GTP analogs, current suppression developed spontaneously and muscarinic inhibition was enhanced. Such spontaneous suppression was antagonized by GDPβS or GTP or by expression of RGS2. These observations were successfully described by a kinetic model representing biochemical steps of the signaling cascade using published rate constants where available. The model supports the following sequence of events for this Gq-coupled signaling: A classical G-protein cycle, including competition for nucleotide-free G-protein by all nucleotide forms and an activation step requiring Mg2+, followed by G-protein–stimulated phospholipase C and hydrolysis of PIP2, and finally PIP2 dissociation from binding sites for inositol lipid on the channels so that KCNQ current was suppressed. Further experiments will be needed to refine some untested assumptions.
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Affiliation(s)
- Byung-Chang Suh
- Department of Physiology and Biophysics, University of Washington School of Medicine, G-424 Health Sciences Building, Box 357290, Seattle, WA 98195-7290, USA
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117
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Higashida H, Hoshi N, Zhang JS, Yokoyama S, Hashii M, Jin D, Noda M, Robbins J. Protein kinase C bound with A-kinase anchoring protein is involved in muscarinic receptor-activated modulation of M-type KCNQ potassium channels. Neurosci Res 2005; 51:231-4. [PMID: 15710486 DOI: 10.1016/j.neures.2004.11.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2004] [Accepted: 11/22/2004] [Indexed: 10/25/2022]
Abstract
The second messenger for closure of M/KCNQ potassium channels in post-ganglionic neurons and central neurons had remained as a 'mystery in the neuroscience field' for over 25 years. However, recently the details of the pathway leading from muscarinic acetylcholine receptor (mAChR)-stimulation to suppression of the M/KCNQ-current were discovered. A key molecule is A-kinase anchoring protein (AKAP; AKAP79 in human, or its rat homolog, AKAP150) which forms a trimeric complex with protein kinase C (PKC) and KCNQ channels. AKAP79 or 150 serves as an adapter that brings the anchored C-kinase to the substrate KCNQ channel to permit the rapid and 'definitive' phosphorylation of serine residues, resulting in avoidance of signal dispersion. Thus, these findings suggest that mAChR-induced short-term modulation (or memory) does occur within the already well-integrated molecular complex, without accompanying Hebbian synapse plasticity. However, before this identity is confirmed, many other modulators which affect M-currents remain to be addressed as intriguing issues.
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Affiliation(s)
- Haruhiro Higashida
- Department of Biophysical Genetics, Kanazawa University Graduate School of Medicine, 13-1 Takara-machi, Kanazawa 920-8640, Japan.
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118
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Prole DL, Marrion NV. Ionic permeation and conduction properties of neuronal KCNQ2/KCNQ3 potassium channels. Biophys J 2004; 86:1454-69. [PMID: 14990473 PMCID: PMC1303981 DOI: 10.1016/s0006-3495(04)74214-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Heteromeric KCNQ2/3 potassium channels are thought to underlie the M-current, a subthreshold potassium current involved in the regulation of neuronal excitability. KCNQ channel subunits are structurally unique, but it is unknown whether these structural differences result in unique conduction properties. Heterologously expressed KCNQ2/3 channels showed a permeation sequence of while showing a conduction sequence of A differential contribution of component subunits to the properties of heteromeric KCNQ2/3 channels was demonstrated by studying homomeric KCNQ2 and KCNQ3 channels, which displayed contrasting ionic selectivities. KCNQ2/3 channels did not exhibit an anomalous mole-fraction effect in mixtures of K(+) and Rb(+). However, extreme voltage-dependence of block by external Cs(+) was indicative of multi-ion pore behavior. Block of KCNQ2/3 channels by external Ba(2+) ions was voltage-independent, demonstrating unusual ionic occupation of the outer pore. Selectivity properties and block of KCNQ2 were altered by mutation of outer pore residues in a manner consistent with the presence of multiple ion-binding sites. KCNQ2/3 channel deactivation kinetics were slowed exclusively by Rb(+), whereas activation of KCNQ2/3 channels was altered by a variety of external permeant ions. These data indicate that KCNQ2/3 channels are multi-ion pores which exhibit distinctive mechanisms of ion conduction and gating.
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Affiliation(s)
- David L Prole
- Department of Pharmacology and MRC Centre for Synaptic Plasticity, University of Bristol, Bristol, United Kingdom
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119
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Li Y, Langlais P, Gamper N, Liu F, Shapiro MS. Dual phosphorylations underlie modulation of unitary KCNQ K(+) channels by Src tyrosine kinase. J Biol Chem 2004; 279:45399-407. [PMID: 15304482 DOI: 10.1074/jbc.m408410200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Src tyrosine kinase suppresses KCNQ (M-type) K(+) channels in a subunit-specific manner representing a mode of modulation distinct from that involving G protein-coupled receptors. We probed the molecular and biophysical mechanisms of this modulation using mutagenesis, biochemistry, and both whole-cell and single channel modes of patch clamp recording. Immunoprecipitation assays showed that Src associates with KCNQ2-5 subunits but phosphorylates only KCNQ3-5. Using KCNQ3 as a background, we found that mutation of a tyrosine in the amino terminus (Tyr-67) or one in the carboxyl terminus (Tyr-349) abolished Src-dependent modulation of heterologously expressed KCNQ2/3 heteromultimers. The tyrosine phosphorylation was much weaker for either the KCNQ3-Y67F or KCNQ3-Y349F mutants and wholly absent in the KCNQ3-Y67F/Y349F double mutant. Biotinylation assays showed that Src activity does not alter the membrane abundance of channels in the plasma membrane. In recordings from cell-attached patches containing a single KCNQ2/3 channel, we found that Src inhibits the open probability of the channels. Kinetic analysis was consistent with the channels having two discrete open times and three closed times. Src activity reduced the durations of the longest open time and lengthened the longest closed time of the channels. The implications for the mechanisms of channel regulation by the dual phosphorylations on both channel termini are discussed.
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Affiliation(s)
- Yang Li
- Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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120
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Romero M, Reboreda A, Sánchez E, Lamas JA. Newly developed blockers of the M-current do not reduce spike frequency adaptation in cultured mouse sympathetic neurons. Eur J Neurosci 2004; 19:2693-702. [PMID: 15147303 DOI: 10.1111/j.1460-9568.2004.03363.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The M-current (I(K(M))) is believed to modulate neuronal excitability by producing spike frequency adaptation (SFA). Inhibitors of M-channels, such as linopirdine and 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone (XE991), enhance depolarization-induced transmitter release and improve learning performance in animal models. As such, they are currently being tested for their therapeutic potential for treating Alzheimer's disease. The activity of these blockers has been associated with the reduction of SFA and the depolarization of the membrane observed when I(K(M)) is inhibited. To test whether this is the case, the perforated patch technique was used to investigate the capacity of I(K(M)) inhibitors to alter the resting membrane potential and to reduce SFA in mouse superior cervical ganglion neurons in culture. Linopirdine and XE991 both proved to be potent blockers of I(K(M)) when the membrane potential was held at -30 mV (IC(50) 2.56 and 0.26 microM, respectively). However, their potency gradually declined upon membrane hyperpolarization and was almost null when the membrane potential was kept at -70 mV, indicating that their blocking activity was voltage dependent. Nevertheless, I(K(M)) could be inhibited at these hyperpolarized voltages by other inhibitors such as oxotremorine-methiodide and barium. Under current-clamp conditions, neither linopirdine (10 microM) nor XE991 (3 microM) was effective in reducing the SFA and both provoked only a small slowly developed depolarization of the membrane (2.27 and 3.0 mV, respectively). In contrast, both barium (1 mM) and oxotremorine-methiodide (10 microM) depolarized mouse superior cervical ganglion neurons by about 10 mV and reduced the SFA. In contrast to classical I(K(M)) inhibitors, the activity of linopirdine and XE991 on the I(K(M)) is voltage dependent and, thus, these newly developed I(K(M)) blockers do not reduce the SFA. These results may shed light on the mode of action of these putative cognition enhancers in vivo.
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Affiliation(s)
- M Romero
- Physiology Section, Department of Functional Biology, Faculty of Sciences, University of Vigo, Lagoas-Marcosende, 36200 Vigo, Spain
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121
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Abstract
We studied modulation of current in human embryonic kidney tsA-201 cells coexpressing rat erg1 channels with M(1) muscarinic receptors. Maximal current was inhibited 30% during muscarinic receptor stimulation, with a small positive shift of the midpoint of activation. Inhibition was attenuated by coexpression of the regulator of G-protein signalling RGS2 or of a dominant-negative protein, G(q), but not by N-ethylmaleimide or C3 toxin. Overexpression of a constitutively active form of G(q) (but not of G(13) or of G(s)) abolished the erg current. Hence it is likely that G(q/11), and not G(i/o) or G(13), mediates muscarinic inhibition. Muscarinic suppression of erg was attenuated by chelating intracellular Ca(2+) to < 1 nm free Ca(2+) with 20 mm BAPTA in the pipette, but suppression was normal if internal Ca(2+) was strongly clamped to a 129 nm free Ca(2+) level with a BAPTA buffer and this was combined with numerous other measures to prevent intracellular Ca(2+) transients (pentosan polysulphate, preincubation with thapsigargin, and removal of extracellular Ca(2+)). Hence a minimum amount of Ca(2+) was necessary for the inhibition, but a Ca(2+) elevation was not. The ATP analogue AMP-PCP did not prevent inhibition. The protein kinase C (PKC) blockers staurosporine and bisindolylmaleimide I did not prevent inhibition, and the PKC-activating phorbol ester PMA did not mimic it. Neither the tyrosine kinase inhibitor genistein nor the tyrosine phosphatase inhibitor dephostatin prevented inhibition by oxotremorine-M. Hence protein kinases are not needed. Experiments with a high concentration of wortmannin were consistent with recovery being partially dependent on PIP(2) resynthesis. Wortmannin did not prevent muscarinic inhibition. Our studies of muscarinic inhibition of erg current suggest a role for phospholipase C, but not the classical downstream messengers, such as PKC or a calcium transient.
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Affiliation(s)
- Wiebke Hirdes
- Department of Physiology and Biophysics, University of Washington School of Medicine, G-424 Health Sciences Building, Box 357290, Seattle, WA 98195-7290, USA
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122
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Synaptic mechanisms modulated by acetylcholine in cerebral cortex. PROGRESS IN BRAIN RESEARCH 2004. [DOI: 10.1016/s0079-6123(03)45005-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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123
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Scott CW, Wilkins DE, Trivedi S, Crankshaw DJ. A medium-throughput functional assay of KCNQ2 potassium channels using rubidium efflux and atomic absorption spectrometry. Anal Biochem 2003; 319:251-7. [PMID: 12871719 DOI: 10.1016/s0003-2697(03)00328-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Heterologous expression of KCNQ2 (Kv7.2) results in the formation of a slowly activating, noninactivating, voltage-gated potassium channel. Using a cell line that stably expresses KCNQ2, we developed a rubidium flux assay to measure the functional activity and pharmacological modulation of this ion channel. Rubidium flux was performed in a 96-well microtiter plate format; rubidium was quantified using an automated atomic absorption spectrometer to enable screening of 1000 data points/day. Cells accumulated rubidium at 37 degrees C in a monoexponential manner with t(1/2)=40min. Treating cells with elevated extracellular potassium caused membrane depolarization and stimulation of rubidium efflux through KCNQ2. The rate of rubidium efflux increased with increasing extracellular potassium: the t(1/2) at 50mM potassium was 5.1 min. Potassium-stimulated efflux was potentiated by the anticonvulsant drug retigabine (EC(50)=0.5 microM). Both potassium-induced and retigabine-facilitated efflux were blocked by TEA (IC(50)s=0.4 and 0.3mM, respectively) and the neurotransmitter release enhancers and putative cognition enhancers linopirdine (IC(50)s=2.3 and 7.1 microM, respectively) and XE991 (IC(50)s=0.3 and 0.9 microM, respectively). Screening a collection of ion channel modulators revealed additional inhibitors including clofilium (IC(50) = 27 microM). These studies extend the pharmacological profile of KCNQ2 and demonstrate the feasibility of using this assay system to rapidly screen for compounds that modulate the function of KCNQ2.
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Affiliation(s)
- Clay W Scott
- Lead Discovery Department, AstraZeneca Pharmaceuticals LP, Wilmington, DE 19810, USA.
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124
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Passmore GM, Selyanko AA, Mistry M, Al-Qatari M, Marsh SJ, Matthews EA, Dickenson AH, Brown TA, Burbidge SA, Main M, Brown DA. KCNQ/M currents in sensory neurons: significance for pain therapy. J Neurosci 2003; 23:7227-36. [PMID: 12904483 PMCID: PMC6740665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/04/2023] Open
Abstract
Neuronal hyperexcitability is a feature of epilepsy and both inflammatory and neuropathic pain. M currents [IK(M)] play a key role in regulating neuronal excitability, and mutations in neuronal KCNQ2/3 subunits, the molecular correlates of IK(M), have previously been linked to benign familial neonatal epilepsy. Here, we demonstrate that KCNQ/M channels are also present in nociceptive sensory systems. IK(M) was identified, on the basis of biophysical and pharmacological properties, in cultured neurons isolated from dorsal root ganglia (DRGs) from 17-d-old rats. Currents were inhibited by the M-channel blockers linopirdine (IC50, 2.1 microm) and XE991 (IC50, 0.26 microm) and enhanced by retigabine (10 microm). The expression of neuronal KCNQ subunits in DRG neurons was confirmed using reverse transcription-PCR and single-cell PCR analysis and by immunofluorescence. Retigabine, applied to the dorsal spinal cord, inhibited C and Adelta fiber-mediated responses of dorsal horn neurons evoked by natural or electrical afferent stimulation and the progressive "windup" discharge with repetitive stimulation in normal rats and in rats subjected to spinal nerve ligation. Retigabine also inhibited responses to intrapaw application of carrageenan in a rat model of chronic pain; this was reversed by XE991. It is suggested that IK(M) plays a key role in controlling the excitability of nociceptors and may represent a novel analgesic target.
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Affiliation(s)
- Gayle M Passmore
- Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom
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125
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Abstract
To quantify the modulation of KCNQ2/3 current by [Ca2+]i and to test if calmodulin (CaM) mediates this action, simultaneous whole-cell recording and Ca2+ imaging was performed on CHO cells expressing KCNQ2/3 channels, either alone, or together with wild-type (wt) CaM, or dominant-negative (DN) CaM. We varied [Ca2+]i from <10 to >400 nM with ionomycin (5 microM) added to either a 2 mM Ca2+, or EGTA-buffered Ca2+-free, solution. Coexpression of wt CaM made KCNQ2/3 currents highly sensitive to [Ca2+]i (IC50 70 +/- 20 nM, max inhibition 73%, n = 10). However, coexpression of DN CaM rendered KCNQ2/3 currents largely [Ca2+]i insensitive (max inhibition 8 +/- 3%, n = 10). In cells without cotransfected CaM, the Ca2+ sensitivity was variable but generally weak. [Ca2+]i modulation of M current in superior cervical ganglion (SCG) neurons followed the same pattern as in CHO cells expressed with KCNQ2/3 and wt CaM, suggesting that endogenous M current is also highly sensitive to [Ca2+]i. Coimmunoprecipitations showed binding of CaM to KCNQ2-5 that was similar in the presence of 5 mM Ca2+ or 5 mM EGTA. Gel-shift analyses suggested Ca2+-dependent CaM binding to an "IQ-like" motif present in the carboxy terminus of KCNQ2-5. We tested whether bradykinin modulation of M current in SCG neurons uses CaM. Wt or DN CaM was exogenously expressed in SCG cells using pseudovirions or the biolistic "gene gun." Using both methods, expression of both wt CaM and DN CaM strongly reduced bradykinin inhibition of M current, but for all groups muscarinic inhibition was unaffected. Cells expressed with wt CaM had strongly reduced tonic current amplitudes as well. We observed similar [Ca2+]i rises by bradykinin in all the groups of cells, indicating that CaM did not affect Ca2+ release from stores. We conclude that M-type currents are highly sensitive to [Ca2+]i and that calmodulin acts as their Ca2+ sensor.
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Affiliation(s)
- Nikita Gamper
- Department of Physiology, MS 7756, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA
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126
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Hadley JK, Passmore GM, Tatulian L, Al-Qatari M, Ye F, Wickenden AD, Brown DA. Stoichiometry of expressed KCNQ2/KCNQ3 potassium channels and subunit composition of native ganglionic M channels deduced from block by tetraethylammonium. J Neurosci 2003; 23:5012-9. [PMID: 12832524 PMCID: PMC6741196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2003] [Revised: 03/17/2003] [Accepted: 03/25/2003] [Indexed: 03/03/2023] Open
Abstract
KCNQ2 and KCNQ3 potassium-channel subunits can form both homomeric and heteromeric channels; the latter are thought to constitute native ganglionic M channels. We have tried to deduce the stoichiometric contributions of KCNQ2 and KCNQ3 subunits to currents generated by the coexpression of KCNQ2 and KCNQ3 cDNA plasmids in Chinese hamster ovary (CHO) cells, and to native M currents in dissociated rat superior cervical ganglion (SCG) neurons, by comparing the block of these currents produced by tetraethylammonium (TEA) with the block of currents generated by a tandem KCNQ3/2 construct. TEA concentration-inhibition curves against coexpressed KCNQ2 plus KCNQ3 currents, and against native M currents in SCG neurons from 6-week-old [postnatal day 45 (P45)] rats, were indistinguishable from those for the expressed tandem construct, and fully accorded with a 1:1 stoichiometry. Inhibition curves in neurons from younger (P17) rats could be better fitted assuming an additional small proportion of current carried by KCNQ2 homomultimers. Single-cell PCR yielded signals for KCNQ2, KCNQ3, and KCNQ5 mRNAs in all SCG neurons tested from both P17 and P45 rats. Quantitative PCR of whole-ganglion mRNA revealed stable levels of KCNQ2 and KCNQ5 mRNA between P7 and P45, but excess and incrementing levels of KCNQ3 mRNA. Increasing levels of KCNQ3 protein between P17 and P45 were confirmed by immunocytochemistry. We conclude that coexpressed KCNQ2 plus KCNQ3 cDNAs generate channels with 1:1 (KCNQ2:KCNQ3) stoichiometry in CHO cells and that native M channels in SCG neurons adopt the same conformation during development, assisted by the increased expression of KCNQ3 mRNA and protein.
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Affiliation(s)
- Jennifer K Hadley
- Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom
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127
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Hoshi N, Zhang JS, Omaki M, Takeuchi T, Yokoyama S, Wanaverbecq N, Langeberg LK, Yoneda Y, Scott JD, Brown DA, Higashida H. AKAP150 signaling complex promotes suppression of the M-current by muscarinic agonists. Nat Neurosci 2003; 6:564-71. [PMID: 12754513 PMCID: PMC3941299 DOI: 10.1038/nn1062] [Citation(s) in RCA: 197] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2003] [Accepted: 03/21/2003] [Indexed: 12/12/2022]
Abstract
M-type (KCNQ2/3) potassium channels are suppressed by activation of G(q/11)-coupled receptors, thereby increasing neuronal excitability. We show here that rat KCNQ2 can bind directly to the multivalent A-kinase-anchoring protein AKAP150. Peptides that block AKAP150 binding to the KCNQ2 channel complex antagonize the muscarinic inhibition of the currents. A mutant form of AKAP150, AKAP(DeltaA), which is unable to bind protein kinase C (PKC), also attenuates the agonist-induced current suppression. Analysis of recombinant KCNQ2 channels suggests that targeting of PKC through association with AKAP150 is important for the inhibition. Phosphorylation of KCNQ2 channels was increased by muscarinic stimulation; this was prevented either by coexpression with AKAP(DeltaA) or pretreatment with PKC inhibitors that compete with diacylglycerol. These inhibitors also reduced muscarinic inhibition of M-current. Our data indicate that AKAP150-bound PKC participates in receptor-induced inhibition of the M-current.
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Affiliation(s)
- Naoto Hoshi
- Department of Biophysical Genetics, Kanazawa University Graduate School of Medicine, 13-1 Takara-machi, Kanazawa, Ishikawa 920-8640, Japan.
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128
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Zhang H, Craciun LC, Mirshahi T, Rohács T, Lopes CMB, Jin T, Logothetis DE. PIP(2) activates KCNQ channels, and its hydrolysis underlies receptor-mediated inhibition of M currents. Neuron 2003; 37:963-75. [PMID: 12670425 DOI: 10.1016/s0896-6273(03)00125-9] [Citation(s) in RCA: 433] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
KCNQ channels belong to a family of potassium ion channels with crucial roles in physiology and disease. Heteromers of KCNQ2/3 subunits constitute the neuronal M channels. Inhibition of M currents, by pathways that stimulate phospholipase C activity, controls excitability throughout the nervous system. Here we show that a common feature of all KCNQ channels is their activation by the signaling membrane phospholipid phosphatidylinositol-bis-phosphate (PIP(2)). We show that wortmannin, at concentrations that prevent recovery from receptor-mediated inhibition of M currents, blocks PIP(2) replenishment to the cell surface. Moreover, we identify a C-terminal histidine residue, immediately proximal to the plasma membrane, mutation of which renders M channels less sensitive to PIP(2) and more sensitive to receptor-mediated inhibition. Finally, native or recombinant channels inhibited by muscarinic agonists can be activated by PIP(2). Our data strongly suggest that PIP(2) acts as a membrane-diffusible second messenger to regulate directly the activity of KCNQ currents.
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Affiliation(s)
- Hailin Zhang
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York University, New York, NY 10029, USA
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129
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Guo J, Schofield GG. Activation of muscarinic m5 receptors inhibits recombinant KCNQ2/KCNQ3 K+ channels expressed in HEK293T cells. Eur J Pharmacol 2003; 462:25-32. [PMID: 12591092 DOI: 10.1016/s0014-2999(03)01323-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A variety of G-protein-coupled receptors regulate membrane excitability via M-type K(+) current (M-current) modulation. Muscarinic m1 and m3 acetylcholine receptors have both been implicated in the modulation of M-current. The muscarinic m5 receptor, like muscarinic m1 and m3 receptors, couples to phospholipase C via a pertussis toxin-insensitive G protein. Since a number of other receptors which activate phospholipase C also modulate M-current, we investigated if muscarinic m5 receptors could modulate recombinant M-type (KCNQ2/KCNQ3) K(+) channels after heterologous expression in human embryonic kidney (HEK) 293T cells. Application of Oxo-tremorine M to HEK293T cells expressing muscarinic m1, m3, or m5 receptors produced a similar robust inhibition of M-current, whereas muscarinic m2 and m4 receptor stimulation was without effect. Muscarinic m1, m3, or m5 receptor stimulation decreased the deactivation time constants of M-current at -50 mV. The inhibition of M-current by stimulation of muscarinic m1, m3, or m5 receptors was insensitive to overnight treatment with pertussis toxin or cholera toxin, which interfere with G(i/o) and G(s) G-protein signaling. These data suggest that muscarinic m1, m3, and m5 receptors inhibit M-channels via the activation of a common G protein.
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Affiliation(s)
- Juan Guo
- Department of Physiology SL-39, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA
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130
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Gamper N, Stockand JD, Shapiro MS. Subunit-specific modulation of KCNQ potassium channels by Src tyrosine kinase. J Neurosci 2003; 23:84-95. [PMID: 12514204 PMCID: PMC6742119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2023] Open
Abstract
We studied regulation by c-Src tyrosine kinase (Src) of KCNQ1-5 channels heterologously expressed in Chinese hamster ovary (CHO) cells and of native M current in rat sympathetic neurons. Using whole-cell patch clamp, we found that Src modulates currents from KCNQ3, KCNQ4, and KCNQ5 homomultimers, KCNQ2/3 heteromultimers and native M current, but not currents from KCNQ1 or KCNQ2 homomultimers. Src overexpression had two effects: a decrease of current amplitude (4- to 15-fold for cloned channels and approximately 3-fold for M current) and a slowing of activation kinetics by 2-fold. Both Src actions were mostly reversed by bath application of the Src inhibitors erbstatin (20 microm) and PP2 (200 nm), and mimicked by the tyrosine phosphatase inhibitor sodium vanadate (100 microm). Immunoprecipitation and immunoblot analysis showed Src-dependent phosphotyrosine signals associated with KCNQ3, KCNQ4, and KCNQ5 but not with KCNQ1 or KCNQ2 that may be tyrosine phosphorylation of the channel subunits. Expression of a dominant negative Src that cannot phosphorylate substrates had no effect on the current and did not induce phosphotyrosine signals associated with KCNQ3-5 subunits, further indicating that Src actions on KCNQ currents are mediated by tyrosine phosphorylation. Immunostaining and confocal analysis showed no effect of Src overexpression on the abundance of KCNQ3 protein in CHO cells. Finally, experiments using cloned KCNQ2/3 channels, Src and M(1) muscarinic receptors, and sympathetic neurons demonstrated that the actions on KCNQ channels by Src and by muscarinic agonists use distinct mechanisms.
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Affiliation(s)
- Nikita Gamper
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA
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131
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Guo J, Schofield GG. Activation of a PTX-insensitive G protein is involved in histamine-induced recombinant M-channel modulation. J Physiol 2002; 545:767-81. [PMID: 12482885 PMCID: PMC2290715 DOI: 10.1113/jphysiol.2002.026583] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The M-type potassium current (I(M)) plays a dominant role in regulating membrane excitability and is modulated by many neurotransmitters. However, except in the case of bradykinin, the signal transduction pathways involved in M-channel modulation have not been fully elucidated. The channels underlying I(M) are produced by the coassembly of KCNQ2 and KCNQ3 channel subunits and can be expressed in heterologous systems where they can be modulated by several neurotransmitter receptors including histamine H(1) receptors. In HEK293T cells, histamine acting via transiently expressed H(1)R produced a strong inhibition of recombinant M-channels but had no overt effects on the voltage dependence or voltage range of I(M) activation. In addition, the modulation of I(M) by histamine was not voltage sensitive, whereas channel gating, particularly deactivation, was accelerated by histamine. Non-hydrolysable guanine nucleotide analogues (GDP-beta-S and GTP-gamma-S) and pertussis toxin (PTX) treatment demonstrated the involvement of a PTX-insensitive G protein in the signal transduction pathway mediating histamine-induced I(M) modulation. Abrogation of the histamine-induced modulation of I(M) by expression of a C-terminal construct of phospholipase C (PLC-beta1-ct), which buffers activated Galpha(q/11) subunits, implicates this G protein alpha subunit in the modulatory pathway. On the other hand, abrogation of the histamine-induced modulation of I(M) by expression of two constructs which buffer free betagamma subunits, transducin (Galphat) and a C-terminal construct of a G protein receptor kinase (MAS-GRK2-ct), implicates betagamma dimers in the modulatory pathway. These findings demonstrate that histamine modulates recombinant M-channels in HEK293T cells via a PTX-insensitive G protein, probably Galpha(q/11), in a similar manner to a number of other G protein-coupled receptors. However, histamine-induced I(M) modulation in HEK293T cells is novel in that betagamma subunits in addition to Galpha(q/11) subunits appear to be involved in the modulation of KCNQ2/3 channel currents.
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Affiliation(s)
- Juan Guo
- Department of Physiology, Tulane University Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, USA
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132
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Roche JP, Westenbroek R, Sorom AJ, Hille B, Mackie K, Shapiro MS. Antibodies and a cysteine-modifying reagent show correspondence of M current in neurons to KCNQ2 and KCNQ3 K+ channels. Br J Pharmacol 2002; 137:1173-86. [PMID: 12466226 PMCID: PMC1573614 DOI: 10.1038/sj.bjp.0704989] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. KCNQ K(+) channels are thought to underlie the M current of neurons. To probe if the KCNQ2 and KCNQ3 subtypes underlie the M current of rat superior cervical ganglia (SCG) neurons and of hippocampus, we raised specific antibodies against them and also used the cysteine-alkylating agent N-ethylmaleimide (NEM) as an additional probe of subunit composition. 2. Tested on tsA-201 (tsA) cells transfected with cloned KCNQ1-5 subunits, our antibodies showed high affinity and selectivity for the appropriate subtype. The antibodies immunostained SCG neurons and hippocampal sections at levels similar to those for channels expressed in tsA cells, indicating that KCNQ2 and KCNQ3 are present in SCG and hippocampal neurons. Some hippocampal regions contained only KCNQ2 or KCNQ3 subunits, suggesting the presence of M currents produced by channels other than KCNQ2/3 heteromultimers. 3. We found that NEM augmented M currents in SCG neurons and KCNQ2/3 currents in tsA cells via strong voltage-independent and modest voltage-dependent actions. Expression of individual KCNQ subunits in tsA cells revealed voltage-independent augmentation of KCNQ2, but not KCNQ1 nor KCNQ3, currents by NEM indicating that this action on SCG M currents likely localizes to KCNQ2. Much of the voltage-independent action is lost after the C242T mutation in KCNQ2. 4. The correspondence of NEM effects on expressed KCNQ2/3 and SCG M currents, along with the antibody labelling, provide further evidence that KCNQ2 and KCNQ3 subunits strongly contribute to the M current of neurons. The site of NEM action may be important for treatment of diseases caused by under-expression of these channels.
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Affiliation(s)
- John P Roche
- Department of Physiology and Biophysics, University of Washington School of Medicine, Box 356540, Seattle, Washington, WA 98195-6540, U.S.A
| | - Ruth Westenbroek
- Department of Pharmacology, University of Washington School of Medicine, Box 356540, Washington, Seattle, WA 98195-6540, U.S.A
| | - Abraham J Sorom
- Department of Anesthesiology, University of Washington School of Medicine, Box 356540, Washington, Seattle, WA 98195-6540, U.S.A
| | - Bertil Hille
- Department of Physiology and Biophysics, University of Washington School of Medicine, Box 356540, Seattle, Washington, WA 98195-6540, U.S.A
| | - Ken Mackie
- Department of Anesthesiology, University of Washington School of Medicine, Box 356540, Washington, Seattle, WA 98195-6540, U.S.A
| | - Mark S Shapiro
- Department of Physiology, University of Texas Health Science Center San Antonio, MS 7756, 7703 Floyd Curl Drive, San Antonio, Texas, TX 78229, U.S.A
- Author for correspondence:
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133
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Bannister RA, Melliti K, Adams BA. Reconstituted slow muscarinic inhibition of neuronal (Ca(v)1.2c) L-type Ca2+ channels. Biophys J 2002; 83:3256-67. [PMID: 12496094 PMCID: PMC1302402 DOI: 10.1016/s0006-3495(02)75327-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Ca(2+) influx through L-type channels is critical for numerous physiological functions. Relatively little is known about modulation of neuronal L-type Ca(2+) channels. We studied modulation of neuronal Ca(V)1.2c channels heterologously expressed in HEK293 cells with each of the known muscarinic acetylcholine receptor subtypes. Galphaq/11-coupled M1, M3, and M5 receptors each produced robust inhibition of Ca(V)1.2c, whereas Galphai/o-coupled M2 and M4 receptors were ineffective. Channel inhibition through M1 receptors was studied in detail and was found to be kinetically slow, voltage-independent, and pertussis toxin-insensitive. Slow inhibition of Ca(V)1.2c was blocked by coexpressing RGS2 or RGS3T or by intracellular dialysis with antibodies directed against Galphaq/11. In contrast, inhibition was not reduced by coexpressing betaARK1ct or Galphat. These results indicate that slow inhibition required signaling by Galphaq/11, but not Gbetagamma, subunits. Slow inhibition did not require Ca(2+) transients or Ca(2+) influx through Ca(V)1.2c channels. Additionally, slow inhibition was insensitive to pharmacological inhibitors of phospholipases, protein kinases, and protein phosphatases. Intracellular BAPTA prevented slow inhibition via a mechanism other than Ca(2+) chelation. The cardiac splice-variant of Ca(V)1.2 (Ca(V)1.2a) and a splice-variant of the neuronal/neuroendocrine Ca(V)1.3 channel also appeared to undergo slow muscarinic inhibition. Thus, slow muscarinic inhibition may be a general characteristic of L-type channels having widespread physiological significance.
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Affiliation(s)
- Roger A Bannister
- Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322, USA
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134
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Shah MM, Mistry M, Marsh SJ, Brown DA, Delmas P. Molecular correlates of the M-current in cultured rat hippocampal neurons. J Physiol 2002; 544:29-37. [PMID: 12356878 PMCID: PMC2290582 DOI: 10.1113/jphysiol.2002.028571] [Citation(s) in RCA: 174] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2002] [Accepted: 08/20/2002] [Indexed: 11/08/2022] Open
Abstract
M-type K(+) currents (I(K(M))) play a key role in regulating neuronal excitability. In sympathetic neurons, M-channels are thought to be composed of a heteromeric assembly of KCNQ2 and KCNQ3 K(+) channel subunits. Here, we have tried to identify the KCNQ subunits that are involved in the generation of I(K(M)) in hippocampal pyramidal neurons cultured from 5- to 7-day-old rats. RT-PCR of either CA1 or CA3 regions revealed the presence of KCNQ2, KCNQ3, KCNQ4 and KCNQ5 subunits. Single-cell PCR of dissociated hippocampal pyramidal neurons gave detectable signals for only KCNQ2, KCNQ3 and KCNQ5; where tested, most also expressed mRNA for the vesicular glutamate transporter VGLUT1. Staining for KCNQ2 and KCNQ5 protein showed punctate fluorescence on both the somata and dendrites of hippocampal neurons. Staining for KCNQ3 was diffusely distributed whereas KCNQ4 was undetectable. In perforated patch recordings, linopirdine, a specific M-channel blocker, fully inhibited I(K(M)) with an IC(50) of 3.6 +/- 1.5 microM. In 70 % of these cells, TEA fully suppressed I(K(M)) with an IC(50) of 0.7 +/- 0.1 mM. In the remaining cells, TEA maximally reduced I(K(M)) by only 59.7 +/- 5.2 % with an IC(50) of 1.4 +/- 0.3 mM; residual I(K(M)) was abolished by linopirdine. Our data suggest that KCNQ2, KCNQ3 and KCNQ5 subunits contribute to I(K(M)) in these neurons and that the variations in TEA sensitivity may reflect differential expression of KCNQ2, KCNQ3 and KCNQ5 subunits.
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Affiliation(s)
- M M Shah
- Wellcome Laboratory for Molecular Pharmacology, Department of Pharmacology, University College London, Gower Street, UK
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135
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Wen H, Levitan IB. Calmodulin is an auxiliary subunit of KCNQ2/3 potassium channels. J Neurosci 2002; 22:7991-8001. [PMID: 12223552 PMCID: PMC6758071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023] Open
Abstract
Calmodulin (CaM) was identified as a KCNQ2 and KCNQ3 potassium channel-binding protein, using a yeast two-hybrid screen. CaM is tethered constitutively to the channel, in the absence or presence of Ca2+, in transfected cells and also coimmunoprecipitates with KCNQ2/3 from mouse brain. The structural elements critical for CaM binding to KCNQ2 lie in two conserved motifs in the proximal half of the channel C-terminal domain. Truncations and point mutations in these two motifs disrupt the interaction. The first CaM-binding motif has a sequence that conforms partially to the consensus IQ motif, but both wild-type CaM and a Ca2+-insensitive CaM mutant bind to KCNQ2. The voltage-dependent activation of the KCNQ2/3 channel also shows no Ca2+ sensitivity, nor is it affected by overexpression of the Ca2+-insensitive CaM mutant. On the other hand, KCNQ2 mutants deficient in CaM binding are unable to generate detectable currents when coexpressed with KCNQ3 in CHO cells, although they are expressed and targeted to the cell membrane and retain the ability to assemble with KCNQ3. A fusion protein containing both of the KCNQ2 CaM-binding motifs competes with the full-length KCNQ2 channel for CaM binding and decreases KCNQ2/3 current density in CHO cells. The correlation of CaM binding with channel function suggests that CaM is an auxiliary subunit of the KCNQ2/3 channel.
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Affiliation(s)
- Hua Wen
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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136
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Guo J, Schofield GG. Histamine inhibits KCNQ2/KCNQ3 channel current via recombinant histamine H(1) receptors. Neurosci Lett 2002; 328:285-8. [PMID: 12147327 DOI: 10.1016/s0304-3940(02)00484-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A variety of agonists are capable of inhibiting M-type K(+) channels via the activation of G-protein coupled receptors which converge on phospholipase-C (PLC) via the activation of G(q/11). Histamine acting via H(1) receptors also activates PLC but to date has not been shown to produce M-current (I(M)) modulation. We postulated that histamine would modulate recombinant M-channels after expressing histamine H(1) receptors in heterologous systems. Expression of KCNQ2 and KCNQ3 K(+) channel subunits by transient transfection in HEK 293T and HeLa cells caused the induction of a slow time-dependent outward current characteristic of I(M). Application of histamine (10 microM) to cells transfected with KCNQ2 and KCNQ3 K(+) channel subunits and H(1) histamine receptors produced a rapid and reversible inhibition. I(M) modulation by histamine was concentration-dependent, half maximal inhibition occurring at 399 nM with a Hill coefficient of 1.09 and was completely abolished by the H(1) receptor selective antagonist, astemizole. Studies of the modulatory effects of histamine on I(M) may aid in elucidating the signal transduction pathway(s) involved in I(M) modulation.
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Affiliation(s)
- Juan Guo
- Department of Physiology SL-39, Tulane University Health Sciences Center, 1430 Tulane Avenue, 70112, New Orleans, LA, USA
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137
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Suh BC, Hille B. Recovery from muscarinic modulation of M current channels requires phosphatidylinositol 4,5-bisphosphate synthesis. Neuron 2002; 35:507-20. [PMID: 12165472 DOI: 10.1016/s0896-6273(02)00790-0] [Citation(s) in RCA: 385] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Suppression of M current channels by muscarinic receptors enhances neuronal excitability. Little is known about the molecular mechanism of this inhibition except the requirement for a specific G protein and the involvement of an unidentified diffusible second messenger. We demonstrate here that intracellular ATP is required for recovery of KCNQ2/KCNQ3 current from muscarinic suppression, with an EC(50) of approximately 0.5 mM. Substitution of nonhydrolyzable ATP analogs for ATP slowed or prevented recovery. ADPbetaS but not ADP also prevented the recovery. Receptor-mediated inhibition was irreversible when recycling of agonist-sensitive pools of phosphatidylinositol-4,5-bisphosphate (PIP(2)) was blocked by lipid kinase inhibitors. Lipid phosphorylation by PI 4-kinase is required for recovery from muscarinic modulation of M current.
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Affiliation(s)
- Byung-Chang Suh
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, WA 98195, USA
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138
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Stemkowski PL, Tse FW, Peuckmann V, Ford CP, Colmers WF, Smith PA. ATP-inhibition of M current in frog sympathetic neurons involves phospholipase C but not Ins P(3), Ca(2+), PKC, or Ras. J Neurophysiol 2002; 88:277-88. [PMID: 12091553 DOI: 10.1152/jn.2002.88.1.277] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Suppression of the voltage-activated, noninactivating K(+) conductance (M conductance; g(M)) by muscarinic agonists, P(2Y) agonists or bradykinin increases neuronal excitability. All agonist effects are mediated, at least in part, via the Gq/(11) class of G protein. We found, using whole cell or perforated patch recording from bullfrog sympathetic B neurons that ATP-induced suppression of g(M) was attenuated by the phospholipase C (PLC) inhibitor, U73122 (IC(50) approximately 0.14 microM) but not by the inactive isomer, U73343. The ability of extracellularly applied U73122 to inhibit PLC was confirmed by its antagonism of ATP-induced elevation of intracellular Ca(2+) as measured by fura-2 photometry. ATP-induced g(M) suppression was not antagonized by the protein kinase C (PKC) inhibitor, chelerythrine (5 microM extracellular +10 microM intracellular), by the Ca(2+)-ATPase inhibitor, thapsigargin (5 microM), or by inositol trisphosphate (InsP(3)) receptor antagonists, heparin (approximaterly 300 microM) or xestospongin C (1.8 microM). The effect of ATP on g(M) was thus dependent on PLC yet independent of PKC and of InsP(3)-induced release of intracellular Ca(2+). We therefore tested the involvement of a PKC-independent action of diacylglycerol (DAG) that could occur via activation of Ras. This low-molecular-weight G protein is activated following DAG binding to Ras-GRP, a neuronal Ras-GTP exchange factor. However, impairment of Ras function by culturing neurons with isoprenylation inhibitors (perillic acid, 0.1 mM, or alpha-hydroxyfarnesyl-phosphonic acid, 10 microM) failed to affect ATP-induced g(M) suppression. Inhibition of MEK (mitogen-activated protein kinase), a downstream target of Ras, by using PD 98059 (10 microM) was also ineffective. The transduction mechanism used by ATP to suppress g(M) in frog sympathetic neurons therefore differs from the PLC-independent mechanism used by muscarine and from the PLC and Ca(2+)-dependent mechanism used by bradykinin and UTP in mammalian ganglia. The possibility remains that "lipid-signaling" mechanisms, perhaps involving PLC-induced depletion of phosphatidylinositol bisphosphate, are involved in PLC-mediated inhibition of g(M) by ATP in amphibian sympathetic neurons.
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Affiliation(s)
- Patrick L Stemkowski
- Department of Pharmacology and University Centre for Neuroscience, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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139
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Abstract
This review addresses the molecular and cellular mechanisms of diseases caused by inherited mutations of ion channels in neurones. Among important recent advances is the elucidation of several dominantly inherited epilepsies caused by mutations of both voltage-gated and ligand-gated ion channels. The neuronal channelopathies show evidence of phenotypic convergence; notably, episodic ataxia can be caused by mutations of either calcium or potassium channels. The channelopathies also show evidence of phenotypic divergence; for instance, different mutations of the same calcium channel gene are associated with familial hemiplegic migraine, episodic or progressive ataxia, coma and epilepsy. Future developments are likely to include the discovery of other ion channel genes associated with inherited and sporadic CNS disorders. The full range of manifestations of inherited ion channel mutations remains to be established.
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Affiliation(s)
- Dimitri M Kullmann
- Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
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140
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Alaburda A, Perrier JF, Hounsgaard J. An M-like outward current regulates the excitability of spinal motoneurones in the adult turtle. J Physiol 2002; 540:875-81. [PMID: 11986376 PMCID: PMC2290271 DOI: 10.1113/jphysiol.2001.015982] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2001] [Accepted: 03/11/2002] [Indexed: 11/08/2022] Open
Abstract
The excitatory action of muscarine on spinal motoneurones was investigated with intracellular recordings in a slice preparation from adult turtles. In these cells muscarine is known to facilitate a persistent inward current mediated by L-type Ca(2+) channels. When this effect was blocked by nifedipine, muscarine still increased the excitability. In voltage clamp, a slowly activating outward current, generated during depolarizing voltage commands and deactivating as a tail current on return to the holding voltage, was reduced by muscarine. This outward current was activated when the voltage was stepped to potentials positive to -60 mV, was voltage sensitive and had a deactivation time constant of approximately 80 ms. These findings are compatible with an M-current. This possibility was also supported by the finding that the current was reduced by XE-991 - a selective blocker of the KCNQ potassium channels underlying M-currents in other cell types. Our findings suggest that an M-like current, mediated by a KCNQ channel, contributes to the intrinsic response properties of motoneurones in the adult spinal cord by increasing adaptation of repetitive firing and decreasing the slope of the frequency-current relation.
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Affiliation(s)
- Aidas Alaburda
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Copenhagen N. DK 2200, Denmark
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141
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Otto JF, Kimball MM, Wilcox KS. Effects of the anticonvulsant retigabine on cultured cortical neurons: changes in electroresponsive properties and synaptic transmission. Mol Pharmacol 2002; 61:921-7. [PMID: 11901232 DOI: 10.1124/mol.61.4.921] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The whole-cell patch-clamp technique was used to examine the effects of retigabine, a novel anticonvulsant drug, on the electroresponsive properties of individual neurons as well as on neurotransmission between monosynaptically connected pairs of cultured mouse cortical neurons. Consistent with its known action on potassium channels, retigabine significantly hyperpolarized the resting membrane potentials of the neurons, decreased input resistance, and decreased the number of action potentials generated by direct current injection. In addition, retigabine potentiated inhibitory postsynaptic currents (IPSCs) mediated by activation of gamma-aminobutyric acid(A) (GABA(A)) receptors. IPSC peak amplitude, 90-to-10% decay time, weighted decay time constant, slow decay time constant, and, consequently, the total charge transfer were all significantly enhanced by retigabine in a dose-dependent manner. This effect was limited to IPSCs; retigabine had no significant effect on excitatory postsynaptic currents (EPSCs) mediated by activation of non-N-methyl-D-aspartate ionotropic glutamate receptors. A form of short-term presynaptic plasticity, paired-pulse depression, was not altered by retigabine, suggesting that its effect on IPSCs is primarily postsynaptic. Consistent with the hypothesis that retigabine increases inhibitory neurotransmission via a direct action on the GABA(A) receptor, the peak amplitudes, 90-to-10% decay times, and total charge transfer of spontaneous miniature IPSCs were also significantly increased. Therefore, retigabine potently reduces excitability in neural circuits via a synergistic combination of mechanisms.
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Affiliation(s)
- James F Otto
- Anticonvulsant Drug Development Program, Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah 84112, USA
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142
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Dupuis DS, Schrøder RL, Jespersen T, Christensen JK, Christophersen P, Jensen BS, Olesen SP. Activation of KCNQ5 channels stably expressed in HEK293 cells by BMS-204352. Eur J Pharmacol 2002; 437:129-37. [PMID: 11890900 DOI: 10.1016/s0014-2999(02)01287-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The novel anti-ischemic compound, BMS-204352 ((3S)-(+)-(5-chloro-2-methoxyphenyl)-1,3-dihydro-3-fluoro-6-(trifluoromethyl)-2H-indol-2-one)), strongly activates the voltage-gated K+ channel KCNQ5 in a concentration-dependent manner with an EC50 of 2.4 microM. At 10 microM, BMS-204352 increased the steady state current at -30 mV by 12-fold, in contrast to the 2-fold increase observed for the other KCNQ channels [Schrøder et al., 2001]. Retigabine ((D-23129; N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester) induced a smaller, yet qualitatively similar effect on KCNQ5. Furthermore, BMS-204352 (10 microM) did not significantly shift the KCNQ5 activation curves (threshold and potential for half-activation, V1/2), as observed for the other KCNQ channels. In the presence of BMS-204352, the activation and deactivation kinetics of the KCNQ5 currents were slowed as the slow activation time constant increased up to 10-fold. The M-current blockers, linopirdine (DuP 996; 3,3-bis(4-pyridinylmethyl)-1-phenylindolin-2-one) and XE991 (10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone), inhibited the activation of the KCNQ5 channel induced by the BMS-204352. Thus, BMS-204352 appears to be an efficacious KCNQ channels activator, and the pharmacological properties of the compound on the KCNQ5 channel seems to be different from what has been obtained on the other KCNQ channels.
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Affiliation(s)
- Delphine S Dupuis
- Department of Medical Physiology, University of Copenhagen, The Panum Institute, 3 Blegdamsvej, DK 2200 Copenhagen N, Denmark.
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143
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Lerche H, Jurkat-Rott K, Lehmann-Horn F. Ion channels and epilepsy. AMERICAN JOURNAL OF MEDICAL GENETICS 2002; 106:146-59. [PMID: 11579435 DOI: 10.1002/ajmg.1582] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Ion channels provide the basis for the regulation of excitability in the central nervous system and in other excitable tissues such as skeletal and heart muscle. Consequently, mutations in ion channel encoding genes are found in a variety of inherited diseases associated with hyper- or hypoexcitability of the affected tissue, the so-called 'channelopathies.' An increasing number of epileptic syndromes belongs to this group of rare disorders: Autosomal dominant nocturnal frontal lobe epilepsy is caused by mutations in a neuronal nicotinic acetylcholine receptor (affected genes: CHRNA4, CHRNB2), benign familial neonatal convulsions by mutations in potassium channels constituting the M-current (KCNQ2, KCNQ3), generalized epilepsy with febrile seizures plus by mutations in subunits of the voltage-gated sodium channel or the GABA(A) receptor (SCN1B, SCN1A, GABRG2), and episodic ataxia type 1-which is associated with epilepsy in a few patients--by mutations within another voltage-gated potassium channel (KCNA1). These rare disorders provide interesting models to study the etiology and pathophysiology of disturbed excitability in molecular detail. On the basis of genetic and electrophysiologic studies of the channelopathies, novel therapeutic strategies can be developed, as has been shown recently for the antiepileptic drug retigabine activating neuronal KCNQ potassium channels.
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MESH Headings
- Ataxia/genetics
- Ataxia/metabolism
- Epilepsies, Myoclonic/genetics
- Epilepsies, Myoclonic/metabolism
- Epilepsies, Partial/genetics
- Epilepsies, Partial/metabolism
- Epilepsy/genetics
- Epilepsy/metabolism
- Epilepsy/therapy
- Epilepsy, Benign Neonatal/genetics
- Epilepsy, Benign Neonatal/metabolism
- Epilepsy, Frontal Lobe/genetics
- Epilepsy, Frontal Lobe/metabolism
- Epilepsy, Generalized/genetics
- Epilepsy, Generalized/metabolism
- Genes, Dominant
- Humans
- Ion Channel Gating
- Ion Channels/chemistry
- Ion Channels/genetics
- Ion Channels/metabolism
- Mutation
- Myokymia/genetics
- Myokymia/metabolism
- Seizures, Febrile/genetics
- Seizures, Febrile/metabolism
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Affiliation(s)
- H Lerche
- Department of Applied Physiology, Univeristy of Ulm, Germany
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144
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Tatulian L, Delmas P, Abogadie FC, Brown DA. Activation of expressed KCNQ potassium currents and native neuronal M-type potassium currents by the anti-convulsant drug retigabine. J Neurosci 2001; 21:5535-45. [PMID: 11466425 PMCID: PMC6762632] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2001] [Revised: 05/11/2001] [Accepted: 05/14/2001] [Indexed: 02/20/2023] Open
Abstract
Retigabine [D-23129; N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester] is a novel anticonvulsant compound that is now in clinical phase II development. It has previously been shown to enhance currents generated by KCNQ2/3 K(+) channels when expressed in Chinese hamster ovary (CHO) cells (Main et al., 2000; Wickenden et al., 2000). In the present study, we have compared the actions of retigabine on KCNQ2/3 currents with those on currents generated by other members of the KCNQ family (homomeric KCNQ1, KCNQ2, KCNQ3, and KCNQ4 channels) expressed in CHO cells and on the native M current in rat sympathetic neurons [thought to be generated by KCNQ2/3 channels (Wang et al., 1998)]. Retigabine produced a hyperpolarizing shift of the activation curves for KCNQ2/3, KCNQ2, KCNQ3, and KCNQ4 currents with differential potencies in the following order: KCNQ3 > KCNQ2/3 > KCNQ2 > KCNQ4, as measured either by the maximum hyperpolarizing shift in the activation curves or by the EC(50) values. In contrast, retigabine did not enhance cardiac KCNQ1 currents. Retigabine also produced a hyperpolarizing shift in the activation curve for native M channels in rat sympathetic neurons. The retigabine-induced current was inhibited by muscarinic receptor stimulation, with similar agonist potency but 25% reduced maximum effect. In unclamped neurons, retigabine produced a hyperpolarization and reduced the number of action potentials produced by depolarizing current injections, without change in action potential configuration.
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Affiliation(s)
- L Tatulian
- Department of Pharmacology and Wellcome Laboratory for Molecular Pharmacology, University College London, London WC1E 6BT, United Kingdom
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145
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Selyanko AA, Hadley JK, Brown DA. Properties of single M-type KCNQ2/KCNQ3 potassium channels expressed in mammalian cells. J Physiol 2001; 534:15-24. [PMID: 11432988 PMCID: PMC2278691 DOI: 10.1111/j.1469-7793.2001.00015.x] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. The single channel properties of KCNQ2/KCNQ3 channels underlying neuronal voltage-dependent M-type potassium currents were studied in cell-attached patches from transfected Chinese hamster ovary (CHO) cells. Macroscopic currents produced by homo- and heteromeric KCNQ2/KCNQ3 channels were measured using the perforated-patch whole-cell technique. 2. Compared with heteromeric KCNQ2 + KCNQ3 channels, homomeric KCNQ2 channels had lower slope conductance (9.0 +/- 0.3 and 5.8 +/- 0.3 pS, respectively) and open probability at 0 mV (0.30 +/- 0.07 and 0.15 +/- 0.03, respectively), consistent with their 3.8-fold smaller macroscopic currents. By contrast, homomeric KCNQ3 channels had the same slope conductance (9.0 +/- 1.1 pS) as KCNQ2 + KCNQ3 channels, and higher open probability (0.59 +/- 0.11), inconsistent with their 12.7-fold smaller macroscopic currents. Thus, KCNQ2 and KCNQ3 subunits may play different roles in the expression of M-type currents, with KCNQ2 ensuring surface expression of underlying channels and KCNQ3 modifying their function. 3. Both in homo- and heteromeric KCNQ2/KCNQ3 channels the shut time distributions were fitted with three, and the open time distributions with two, exponential components. By measuring these and other parameters (e.g. conductance and open probability) KCNQ2/ KCNQ3 channels can be shown to resemble previously characterised neuronal M-type channels.
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Affiliation(s)
- A A Selyanko
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
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146
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Coghlan MJ, Carroll WA, Gopalakrishnan M. Recent developments in the biology and medicinal chemistry of potassium channel modulators: update from a decade of progress. J Med Chem 2001; 44:1627-53. [PMID: 11356099 DOI: 10.1021/jm000484+] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M J Coghlan
- Neurological and Urological Diseases Research, Pharmaceutical Products Division, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, Illinois 60064, USA.
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147
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Raza M, Pal S, Rafiq A, DeLorenzo RJ. Long-term alteration of calcium homeostatic mechanisms in the pilocarpine model of temporal lobe epilepsy. Brain Res 2001; 903:1-12. [PMID: 11382382 DOI: 10.1016/s0006-8993(01)02127-8] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The pilocarpine model of temporal lobe epilepsy is an animal model that shares many of the clinical and pathophysiological characteristics of temporal lobe or limbic epilepsy in humans. This model of acquired epilepsy produces spontaneous recurrent seizure discharges following an initial brain injury produced by pilocarpine-induced status epilepticus. Understanding the molecular mechanisms mediating these long lasting changes in neuronal excitability would provide an important insight into developing new strategies for the treatment and possible prevention of this condition. Our laboratory has been studying the role of alterations in calcium and calcium-dependent systems in mediating some of the long-term neuroplasticity changes associated with epileptogenesis. In this study, [Ca(2+)](i) imaging fluorescence microscopy was performed on CA1 hippocampal neurons acutely isolated from control and chronically epileptic animals at 1 year after the induction of epileptogenesis with two different fluorescent dyes (Fura-2 and Fura-FF) having high and low affinities for [Ca(2+)](i). The high affinity Ca(2+) indicator Fura-2 was utilized to evaluate [Ca(2+)](i) levels up to 900 nM and the low affinity indicator Fura-FF was employed for evaluating [Ca(2+)](i) levels above this range. Baseline [Ca(2+)](i) levels and the ability to restore resting [Ca(2+)](i) levels after a brief exposure to several glutamate concentrations in control and epileptic neurons were evaluated. Epileptic neurons demonstrated a statistically significantly higher baseline [Ca(2+)](i) level in comparison to age-matched control animals. This alteration in basal [Ca(2+)](i) levels persisted up to 1 year after the induction of epileptogenesis. In addition, the epileptic neurons were unable to rapidly restore [Ca(2+)](i) levels to baseline following the glutamate-induced [Ca(2+)](i) loads. These changes in Ca(2+) regulation were not produced by a single seizure and were not normalized by controlling the seizures in the epileptic animals with anticonvulsant treatment. Peak [Ca(2+)](i) levels in response to different concentrations of glutamate were the same in both epileptic and control neurons. Thus, glutamate produced the same initial [Ca(2+)](i) load in both epileptic and control neurons. Characterization of the viability of acutely isolated neurons from control and epileptic animals utilizing standard techniques to identify apoptotic or necrotic neurons demonstrated that epileptic neurons had no statistically significant difference in viability compared to age-matched controls. These results provide the first direct measurement of [Ca(2+)](i) levels in an intact model of epilepsy and indicate that epileptogenesis in this model produced long-lasting alterations in [Ca(2+)](i) homeostatic mechanisms that persist for up to 1 year after induction of epileptogenesis. These observations suggest that altered [Ca(2+)](i) homeostatic mechanisms may underlie some aspects of the epileptic phenotype and contribute to the persistent neuroplasticity changes associated with epilepsy.
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Affiliation(s)
- M Raza
- Department of Neurology, Medical College of Virginia, Virginia Commonwealth University, P.O. Box 980599, Richmond, VA 23298-0599, USA
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148
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Melliti K, Meza U, Adams BA. RGS2 blocks slow muscarinic inhibition of N-type Ca(2+) channels reconstituted in a human cell line. J Physiol 2001; 532:337-47. [PMID: 11306654 PMCID: PMC2278552 DOI: 10.1111/j.1469-7793.2001.0337f.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
1. Native N-type Ca(2+) channels undergo sustained inhibition through a slowly activating pathway linked to M1 muscarinic acetylcholine receptors and Galphaq/11 proteins. Little is known concerning the regulation of this slow inhibitory pathway. We have reconstituted slow muscarinic inhibition of N-type channels in HEK293 cells (a human embryonic kidney cell line) by coexpressing cloned alpha1B (Ca(V)2.2) Ca(2+) channel subunits and M1 receptors. Expressed Ca(2+) currents were recorded using standard whole-cell, ruptured-patch techniques. 2. Rapid application of carbachol produced two kinetically distinct components of Ca(2+) channel inhibition. The fast component of inhibition had a time constant of < 1 s, whereas the slow component had a time constant of 5-40 s. Neither component of inhibition was reduced by pertussis toxin (PTX) or staurosporine. 3. The fast component of inhibition was selectively blocked by the Gbetagamma-binding region of beta-adrenergic receptor kinase 1, suggesting that fast inhibition is mediated by Gbetagamma released from Galphaq/11. 4. The slow component of inhibition was selectively blocked by regulator of G protein signalling 2 (RGS2), which preferentially interacts with Galphaq/11 proteins. RGS2 also attenuated channel inhibition produced by intracellular dialysis with non-hydrolysable GTPgammaS. Together these results suggest that RGS2 selectively blocked slow inhibition by functioning as an effector antagonist, rather than as a GTPase-accelerating protein (GAP). 5. These experiments demonstrate that slow muscarinic inhibition of N-type Ca(2+) channels can be reconstituted in non-neuronal cells, and that RGS2 can selectively block slow muscarinic inhibition while leaving fast muscarinic inhibition intact. These results identify RGS2 as a potential physiological regulator of the slow muscarinic pathway.
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Affiliation(s)
- K Melliti
- Department of Biology, Utah State University, Logan 84322-5305, USA
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149
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Abstract
KCNQ genes encode a growing family of six transmembrane domains, single pore-loop, K(+) channel alpha-subunits that have a wide range of physiological correlates. KCNQ1 (KvLTQ1) is co-assembled with the product of the KCNE1 (minimal K(+)-channel protein) gene in the heart to form a cardiac-delayed rectifier-like K(+) current. Mutations in this channel can cause one form of inherited long QT syndrome (LQT1), as well as being associated with a form of deafness. KCNQ1 can also co-assemble with KCNE3, and may be the molecular correlate of the cyclic AMP-regulated K(+) current present in colonic crypt cells. KCNQ2 and KCNQ3 heteromultimers are thought to underlie the M-current; mutations in these genes may cause an inherited form of juvenile epilepsy. The KCNQ4 gene is thought to encode the molecular correlate of the I(K,n) in outer hair cells of the cochlea and I(K,L) in Type I hair cells of the vestibular apparatus, mutations in which lead to a form of inherited deafness. The recently identified KCNQ5 gene is expressed in brain and skeletal muscle, and can co-assemble with KCNQ3, suggesting it may also play a role in the M-current heterogeneity. This review will set this family of K(+) channels amongst the other known families. It will highlight the genes, physiology, pharmacology, and pathophysiology of this recently discovered, but important, family of K(+) channels.
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Affiliation(s)
- J Robbins
- Sensory Function Group, Centre for Neuroscience Research, King's College, Guy's Campus, London SE1 1UL, UK.
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150
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Brown BS, Yu SP. Modulation and genetic identification of the M channel. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2001; 73:135-66. [PMID: 10958929 DOI: 10.1016/s0079-6107(00)00004-3] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Potassium channels constitute a superfamily of the most diversified ion channels, acting in delicate and accurate ways to control or modify many physiological and pathological functions including membrane excitability, transmitter release, cell proliferation and cell degeneration. The M-type channel is a unique ligand-regulated and voltage-gated K(+) channel showing distinct physiological and pharmacological characteristics. This review will cover some important progress in the study of M channel modulation, particularly focusing on membrane transduction mechanisms. The K(+) channel genes corresponding to the M channel have been identified and will be reviewed in detail. It has been a long journey since the discovery of M current in 1980 to our present understanding of the mysterious mechanisms for M channel modulation; a journey which exemplifies tremendous achievements in ion channel research and exciting discoveries of elaborate modulatory systems linked to these channels. While substantial evidence has accumulated, challenging questions remain to be answered.
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Affiliation(s)
- B S Brown
- General Pharmacology Department, DuPont Pharmaceuticals Company, Wilmington, DE 19880-0400, USA
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