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Gao S, Yao X, Chen J, Huang G, Fan X, Xue L, Li Z, Wu T, Zheng Y, Huang J, Jin X, Wang Y, Wang Z, Yu Y, Liu L, Pan X, Song C, Yan N. Structural basis for human Ca v1.2 inhibition by multiple drugs and the neurotoxin calciseptine. Cell 2023; 186:5363-5374.e16. [PMID: 37972591 DOI: 10.1016/j.cell.2023.10.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 03/16/2023] [Accepted: 10/04/2023] [Indexed: 11/19/2023]
Abstract
Cav1.2 channels play crucial roles in various neuronal and physiological processes. Here, we present cryo-EM structures of human Cav1.2, both in its apo form and in complex with several drugs, as well as the peptide neurotoxin calciseptine. Most structures, apo or bound to calciseptine, amlodipine, or a combination of amiodarone and sofosbuvir, exhibit a consistent inactivated conformation with a sealed gate, three up voltage-sensing domains (VSDs), and a down VSDII. Calciseptine sits on the shoulder of the pore domain, away from the permeation path. In contrast, when pinaverium bromide, an antispasmodic drug, is inserted into a cavity reminiscent of the IFM-binding site in Nav channels, a series of structural changes occur, including upward movement of VSDII coupled with dilation of the selectivity filter and its surrounding segments in repeat III. Meanwhile, S4-5III merges with S5III to become a single helix, resulting in a widened but still non-conductive intracellular gate.
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Affiliation(s)
- Shuai Gao
- Department of Urology, Zhongnan Hospital of Wuhan University, TaiKang Center for Life and Medical Sciences, School of Pharmaceutical Sciences, Wuhan University, Wuhan 430071, China; Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
| | - Xia Yao
- Department of Urology, Zhongnan Hospital of Wuhan University, TaiKang Center for Life and Medical Sciences, School of Pharmaceutical Sciences, Wuhan University, Wuhan 430071, China; Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Jiaofeng Chen
- Beijing Frontier Research Center for Biological Structures, Tsinghua-Peking Center for Life Sciences, State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Gaoxingyu Huang
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Institute of Biology, Westlake Institute for Advanced Study, Zhejiang Provincial Laboratory of Life Sciences and Biomedicine, Hangzhou, Zhejiang 310024, China
| | - Xiao Fan
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Lingfeng Xue
- Center for Quantitative Biology, Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
| | - Zhangqiang Li
- Beijing Frontier Research Center for Biological Structures, Tsinghua-Peking Center for Life Sciences, State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Tong Wu
- Beijing Frontier Research Center for Biological Structures, Tsinghua-Peking Center for Life Sciences, State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yupeng Zheng
- Tsinghua-Peking Center for Life Sciences, Ministry of Education Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Center for Synthetic and Systems Biology, Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Jian Huang
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
| | - Xueqin Jin
- Beijing Frontier Research Center for Biological Structures, Tsinghua-Peking Center for Life Sciences, State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yan Wang
- Department of Biological Sciences, St. John's University, Queens, NY 11439, USA
| | - Zhifei Wang
- Department of Biological Sciences, St. John's University, Queens, NY 11439, USA
| | - Yong Yu
- Department of Biological Sciences, St. John's University, Queens, NY 11439, USA
| | - Lei Liu
- Tsinghua-Peking Center for Life Sciences, Ministry of Education Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Center for Synthetic and Systems Biology, Department of Chemistry, Tsinghua University, Beijing 100084, China
| | - Xiaojing Pan
- Beijing Frontier Research Center for Biological Structures, Tsinghua-Peking Center for Life Sciences, State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Shenzhen Medical Academy of Research and Translation, Shenzhen, Guangdong 518107, China
| | - Chen Song
- Center for Quantitative Biology, Peking-Tsinghua Center for Life Sciences, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China.
| | - Nieng Yan
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA; Beijing Frontier Research Center for Biological Structures, Tsinghua-Peking Center for Life Sciences, State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Shenzhen Medical Academy of Research and Translation, Shenzhen, Guangdong 518107, China.
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Zhang Y, Li D, Darwish Y, Fu X, Trussell LO, Huang H. KCNQ Channels Enable Reliable Presynaptic Spiking and Synaptic Transmission at High Frequency. J Neurosci 2022; 42:3305-3315. [PMID: 35256530 PMCID: PMC9034779 DOI: 10.1523/jneurosci.0363-20.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2020] [Revised: 02/06/2022] [Accepted: 02/26/2022] [Indexed: 11/21/2022] Open
Abstract
The presynaptic action potential (AP) is required to drive calcium influx into nerve terminals, resulting in neurotransmitter release. Accordingly, the AP waveform is crucial in determining the timing and strength of synaptic transmission. The calyx of Held nerve terminals of rats of either sex showed minimum changes in AP waveform during high-frequency AP firing. We found that the stability of the calyceal AP waveform requires KCNQ (KV7) K+ channel activation during high-frequency spiking activity. High-frequency presynaptic spikes gradually led to accumulation of KCNQ channels in open states which kept interspike membrane potential sufficiently negative to maintain Na+ channel availability. Blocking KCNQ channels during stimulus trains led to inactivation of presynaptic Na+, and to a lesser extent KV1 channels, thereby reducing the AP amplitude and broadening AP duration. Moreover, blocking KCNQ channels disrupted the stable calcium influx and glutamate release required for reliable synaptic transmission at high frequency. Thus, while KCNQ channels are generally thought to prevent hyperactivity of neurons, we find that in axon terminals these channels function to facilitate reliable high-frequency synaptic signaling needed for sensory information processing.SIGNIFICANCE STATEMENT The presynaptic spike results in calcium influx required for neurotransmitter release. For this reason, the spike waveform is crucial in determining the timing and strength of synaptic transmission. Auditory information is encoded by spikes phase locked to sound frequency at high rates. The calyx of Held nerve terminals in the auditory brainstem show minimum changes in spike waveform during high-frequency spike firing. We found that activation of KCNQ K+ channel builds up during high-frequency firing and its activation helps to maintain a stable spike waveform and reliable synaptic transmission. While KCNQ channels are generally thought to prevent hyperexcitability of neurons, we find that in axon terminals these channels function to facilitate high-frequency synaptic signaling during auditory information processing.
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Affiliation(s)
- Yihui Zhang
- Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118
| | - Dainan Li
- Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118
| | - Youad Darwish
- Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118
| | - Xin Fu
- Brain Institute, Tulane University, New Orleans, LA 70118
| | - Laurence O Trussell
- Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, OR 97239
| | - Hai Huang
- Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118
- Brain Institute, Tulane University, New Orleans, LA 70118
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Zhang Y, Zhang X, Liu C, Hu C. Regulation of K + Conductance by a Hydrogen Bond in Kv2.1, Kv2.2, and Kv1.2 Channels. Membranes (Basel) 2021; 11:190. [PMID: 33803465 PMCID: PMC8001480 DOI: 10.3390/membranes11030190] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 03/01/2021] [Accepted: 03/05/2021] [Indexed: 11/17/2022]
Abstract
The slow inactivation of voltage-gated potassium (Kv) channels plays an important role in controlling cellular excitability. Recently, the two hydrogen bonds (H-bonds) formed by W434-D447 and T439-Y445 have been reported to control the slow inactivation in Shaker potassium channels. The four residues are highly conserved among Kv channels. Our objective was to find the roles of the two H-bonds in controlling the slow inactivation of mammalian Kv2.1, Kv2.2, and Kv1.2 channels by point mutation and patch-clamp recording studies. We found that mutations of the residues equivalent to W434 and T439 in Shaker did not change the slow inactivation of the Kv2.1, Kv2.2, and Kv1.2 channels. Surprisingly, breaking of the inter-subunit H-bond formed by W366 and Y376 (Kv2.1 numbering) by various mutations resulted in the complete loss of K+ conductance of the three Kv channels. In conclusion, we found differences in the H-bonds controlling the slow inactivation of the mammalian Kv channels and Shaker channels. Our data provided the first evidence, to our knowledge, that the inter-subunit H-bond formed by W366 and Y376 plays an important role in regulating the K+ conductance of mammalian Kv2.1, Kv2.2, and Kv1.2 channels.
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Affiliation(s)
| | | | | | - Changlong Hu
- Department of Physiology and Biophysics, Institutes of Brain Science, School of Life Sciences, Fudan University, Shanghai 200032, China; (Y.Z.); (X.Z.); (C.L.)
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Zhang XY, Bi RY, Zhang P, Gan YH. Veratridine modifies the gating of human voltage-gated sodium channel Nav1.7. Acta Pharmacol Sin 2018; 39:1716-1724. [PMID: 29950616 DOI: 10.1038/s41401-018-0065-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 06/05/2018] [Indexed: 01/22/2023] Open
Abstract
Veratridine is a lipid-soluble neurotoxin derived from plants in the family Liliaceae. It has been broadly investigated for its action as a sodium channel agonist. However, the effects of veratridine on subtypes of sodium channels, especially Nav1.7, remain to be studied. Here, we investigated the effects of veratridine on human Nav1.7 ectopically expressed in HEK293A cells and recorded Nav1.7 currents from the cells using whole-cell patch clamp technique. We found that veratridine exerted a dose-dependent inhibitory effect on the peak current of Nav1.7, with the half-maximal inhibition concentration (IC50) of 18.39 µM. Meanwhile, veratridine also elicited tail current (linearly) and sustained current [half-maximal concentration (EC50): 9.53 µM], also in a dose-dependent manner. Veratridine (75 µM) shifted the half-maximal activation voltage of the Nav1.7 activation curve in the hyperpolarized direction, from -21.64 ± 0.75 mV to -28.14 ± 0.66 mV, and shifted the half-inactivation voltage of the steady-state inactivation curve from -59.39 ± 0.39 mV to -73.78 ± 0.5 mV. An increased frequency of stimulation decreased the peak and tail currents of Nav1.7 for each pulse along with pulse number, and increased the accumulated tail current at the end of train stimulation. These findings reveal the different modulatory effects of veratridine on the Nav1.7 peak current and tail current.
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Burel S, Coyan FC, Lorenzini M, Meyer MR, Lichti CF, Brown JH, Loussouarn G, Charpentier F, Nerbonne JM, Townsend RR, Maier LS, Marionneau C. C-terminal phosphorylation of Na V1.5 impairs FGF13-dependent regulation of channel inactivation. J Biol Chem 2017; 292:17431-17448. [PMID: 28882890 DOI: 10.1074/jbc.m117.787788] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Revised: 08/23/2017] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated Na+ (NaV) channels are key regulators of myocardial excitability, and Ca2+/calmodulin-dependent protein kinase II (CaMKII)-dependent alterations in NaV1.5 channel inactivation are emerging as a critical determinant of arrhythmias in heart failure. However, the global native phosphorylation pattern of NaV1.5 subunits associated with these arrhythmogenic disorders and the associated channel regulatory defects remain unknown. Here, we undertook phosphoproteomic analyses to identify and quantify in situ the phosphorylation sites in the NaV1.5 proteins purified from adult WT and failing CaMKIIδc-overexpressing (CaMKIIδc-Tg) mouse ventricles. Of 19 native NaV1.5 phosphorylation sites identified, two C-terminal phosphoserines at positions 1938 and 1989 showed increased phosphorylation in the CaMKIIδc-Tg compared with the WT ventricles. We then tested the hypothesis that phosphorylation at these two sites impairs fibroblast growth factor 13 (FGF13)-dependent regulation of NaV1.5 channel inactivation. Whole-cell voltage-clamp analyses in HEK293 cells demonstrated that FGF13 increases NaV1.5 channel availability and decreases late Na+ current, two effects that were abrogated with NaV1.5 mutants mimicking phosphorylation at both sites. Additional co-immunoprecipitation experiments revealed that FGF13 potentiates the binding of calmodulin to NaV1.5 and that phosphomimetic mutations at both sites decrease the interaction of FGF13 and, consequently, of calmodulin with NaV1.5. Together, we have identified two novel native phosphorylation sites in the C terminus of NaV1.5 that impair FGF13-dependent regulation of channel inactivation and may contribute to CaMKIIδc-dependent arrhythmogenic disorders in failing hearts.
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Affiliation(s)
- Sophie Burel
- From the l'Institut du Thorax, INSERM, CNRS, UNIV Nantes, Nantes 44007, France
| | - Fabien C Coyan
- From the l'Institut du Thorax, INSERM, CNRS, UNIV Nantes, Nantes 44007, France
| | - Maxime Lorenzini
- From the l'Institut du Thorax, INSERM, CNRS, UNIV Nantes, Nantes 44007, France
| | | | - Cheryl F Lichti
- the Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, Texas 77555
| | - Joan H Brown
- the Department of Pharmacology, University of California at San Diego, La Jolla, California 92093-0636, and
| | - Gildas Loussouarn
- From the l'Institut du Thorax, INSERM, CNRS, UNIV Nantes, Nantes 44007, France
| | - Flavien Charpentier
- From the l'Institut du Thorax, INSERM, CNRS, UNIV Nantes, Nantes 44007, France
| | | | - R Reid Townsend
- Internal Medicine, and.,Cell Biology and Physiology, Washington University Medical School, St. Louis, Missouri 63110
| | - Lars S Maier
- the Department of Internal Medicine II, University Heart Center, University Hospital Regensburg, D-93042 Regensburg, Germany
| | - Céline Marionneau
- From the l'Institut du Thorax, INSERM, CNRS, UNIV Nantes, Nantes 44007, France,
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Bosch MK, Carrasquillo Y, Ransdell JL, Kanakamedala A, Ornitz DM, Nerbonne JM. Intracellular FGF14 (iFGF14) Is Required for Spontaneous and Evoked Firing in Cerebellar Purkinje Neurons and for Motor Coordination and Balance. J Neurosci 2015; 35:6752-69. [PMID: 25926453 DOI: 10.1523/JNEUROSCI.2663-14.2015] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Mutations in FGF14, which encodes intracellular fibroblast growth factor 14 (iFGF14), have been linked to spinocerebellar ataxia (SCA27). In addition, mice lacking Fgf14 (Fgf14(-/-)) exhibit an ataxia phenotype resembling SCA27, accompanied by marked changes in the excitability of cerebellar granule and Purkinje neurons. It is not known, however, whether these phenotypes result from defects in neuronal development or if they reflect a physiological requirement for iFGF14 in the adult cerebellum. Here, we demonstrate that the acute and selective Fgf14-targeted short hairpin RNA (shRNA)-mediated in vivo "knock-down" of iFGF14 in adult Purkinje neurons attenuates spontaneous and evoked action potential firing without measurably affecting the expression or localization of voltage-gated Na(+) (Nav) channels at Purkinje neuron axon initial segments. The selective shRNA-mediated in vivo "knock-down" of iFGF14 in adult Purkinje neurons also impairs motor coordination and balance. Repetitive firing can be restored in Fgf14-targeted shRNA-expressing Purkinje neurons, as well as in Fgf14(-/-) Purkinje neurons, by prior membrane hyperpolarization, suggesting that the iFGF14-mediated regulation of the excitability of mature Purkinje neurons depends on membrane potential. Further experiments revealed that the loss of iFGF14 results in a marked hyperpolarizing shift in the voltage dependence of steady-state inactivation of the Nav currents in adult Purkinje neurons. We also show here that expressing iFGF14 selectively in adult Fgf14(-/-) Purkinje neurons rescues spontaneous firing and improves motor performance. Together, these results demonstrate that iFGF14 is required for spontaneous and evoked action potential firing in adult Purkinje neurons, thereby controlling the output of these cells and the regulation of motor coordination and balance.
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Abstract
Voltage-gated potassium (Kv) channels enable potassium efflux and membrane repolarization in excitable tissues. Many Kv channels undergo a progressive loss of ion conductance in the presence of a prolonged voltage stimulus, termed slow inactivation, but the atomic determinants that regulate the kinetics of this process remain obscure. Using a combination of synthetic amino acid analogs and concatenated channel subunits we establish two H-bonds near the extracellular surface of the channel that endow Kv channels with a mechanism to time the entry into slow inactivation: an intra-subunit H-bond between Asp447 and Trp434 and an inter-subunit H-bond connecting Tyr445 to Thr439. Breaking of either interaction triggers slow inactivation by means of a local disruption in the selectivity filter, while severing the Tyr445–Thr439 H-bond is likely to communicate this conformational change to the adjacent subunit(s). DOI:http://dx.doi.org/10.7554/eLife.01289.001 Proteins are made from long chains of smaller molecules, called amino acids. These chains twist and bend into complex three-dimensional shapes, and sometimes two or more chains, or ‘subunits’, are packed into a protein. These shapes are often held together by hydrogen bonds between some of the amino acids. Moreover, since the shape of a protein defines its function, some proteins must be able to switch between different shapes to function properly. Ion channels are proteins that form pores through cell membranes, allowing ions to flow in and out of the cell. Potassium ion channels, which are found in neurons and heart muscle cells, have four subunits that move to open or close the central pore in response to various signals. The closing of the channels can be ‘fast’ or ‘slow’. When the channels are closed quickly (called fast inactivation), a small part of the protein ‘plugs’ the pore from the inside of the cell. However, the mechanism behind slow inactivation remained obscure. It was thought to involve hydrogen bonds between some of the bulky amino acids that are found at the edge the pore. However, testing this hypothesis—by replacing these amino acids with alternatives that cannot form hydrogen bonds—was tricky because none of the 20 naturally occurring amino acids were alike enough to be suitable replacements. Now, Pless et al. have overcome this limitation by using synthetic amino acids that form hydrogen bonds that are stronger or weaker than those formed by the amino acids they are replacing. The results suggest that two types of hydrogen bond keep the pore open: one is a bond between two amino acids in the same subunit, and the other is an inter-subunit bond between amino acids in neighbouring subunits. Pless et al. suggest that opening the channel causes small movements that gradually weaken, and eventually break, these bonds in one of the four subunits. Specific amino acids within the pore are then free to twist and—via a cascade of similar movements in the other three subunits—block the pore and halt the flow of ions. As such, these networks of hydrogen bonds act as pre-set breaking points allowing channels to close, even in response to continued stimulation. Since regulated potassium channel activity underpins healthy neurons and heart muscles; understanding what controls their inactivation rate may lead to new approaches to tune their activity and treatments for important diseases. DOI:http://dx.doi.org/10.7554/eLife.01289.002
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Affiliation(s)
- Stephan A Pless
- Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada
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Abstract
1. RP58866 possesses a unique electrophysiological property: highly effective against various types of arrhythmias including ventricular fibrillation in animal models, noticeably those occurring during ischaemia with depolarized membrane due to elevated extracellular K+ concentrations. To understand the potential ionic mechanisms, we performed detailed studies on the effects of RP58866 on the HERG channels expressed in Xenopus oocytes, which are believed to be important compositions of the rapid component of delayed rectifier K+ current in the hearts. 2. RP58866 significantly inhibited the HERG channels in a concentration-dependent manner, with approximately 50% decrease in the current amplitude at a concentration of 1 microM. RP58866 produced more pronounced inhibition with voltage protocols which favoured inactivation of the HERG channels. It caused substantial negative shift of the inactivation curves but did not alter the activation properties. The inhibition was considerably relieved by elevating [K+]o from 5 - 20 mM, which weakened the channel inactivation. More importantly, the potency was reduced by approximately 100 fold on the mutated HERG channels (S631A) in which the C-type inactivation was substantially weakened. 4. We conclude that blockade of the HERG channels by RP58866 is mainly associated with the binding of the drugs to the inactivated channels. This unique property of HERG blockade might explain some previously reported but unexplained observations: RP58866 maintains its efficacy in APD prolongation with depolarized membrane potential and in arrhythmias during ischaemia with manifested membrane depolarization.
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Affiliation(s)
- Huizhen Wang
- Research Center, Montreal Heart Institute, 5000 Belanger East, Montreal, Quebec H1T 1C8, Canada
| | - Hong Shi
- Research Center, Montreal Heart Institute, 5000 Belanger East, Montreal, Quebec H1T 1C8, Canada
| | - Zhiguo Wang
- Research Center, Montreal Heart Institute, 5000 Belanger East, Montreal, Quebec H1T 1C8, Canada
- Department of Medicine, University of Montreal, Montreal, Quebec H3C 3J7, Canada
- Author for correspondence:
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Abstract
C-type inactivation in Shaker potassium channels inhibits K+ permeation. The associated structural changes appear to involve the outer region of the pore. Recently, we have shown that C-type inactivation involves a change in the selectivity of the Shaker channel, such that C-type inactivated channels show maintained voltage-sensitive activation and deactivation of Na+ and Li+ currents in K+-free solutions, although they show no measurable ionic currents in physiological solutions. In addition, it appears that the effective block of ion conduction produced by the mutation W434F in the pore region may be associated with permanent C-type inactivation of W434F channels. These conclusions predict that permanently C-type inactivated W434F channels would also show Na+ and Li+ currents (in K+-free solutions) with kinetics similar to those seen in C-type-inactivated Shaker channels. This paper confirms that prediction and demonstrates that activation and deactivation parameters for this mutant can be obtained from macroscopic ionic current measurements. We also show that the prolonged Na+ tail currents typical of C-type inactivated channels involve an equivalent prolongation of the return of gating charge, thus demonstrating that the kinetics of gating charge return in W434F channels can be markedly altered by changes in ionic conditions.
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Affiliation(s)
- J G Starkus
- Max-Planck Society, Research Unit Molecular and Cellular Biophysics, D-07747 Jena, Germany
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10
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Abstract
C-type inactivation of Shaker potassium channels involves entry into a state (or states) in which the inactivated channels appear nonconducting in physiological solutions. However, when Shaker channels, from which fast N-type inactivation has been removed by NH2-terminal deletions, are expressed in Xenopus oocytes and evaluated in inside-out patches, complete removal of K+ ions from the internal solution exposes conduction of Na+ and Li+ in C-type inactivated conformational states. The present paper uses this observation to investigate the properties of ion conduction through C-type inactivated channel states, and demonstrates that both activation and deactivation can occur in C-type states, although with slower than normal kinetics. Channels in the C-type states appear "inactivated" (i.e., nonconducting) in physiological solutions due to the summation of two separate effects: first, internal K+ ions prevent Na+ ions from permeating through the channel; second, C-type inactivation greatly reduces the permeability of K+ relative to the permeability of Na+, thus altering the ion selectivity of the channel.
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Affiliation(s)
- J G Starkus
- Research Unit Molecular and Cellular Biophysics, Max Planck Society, D-07747 Jena, Germany
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