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Pumroy RA, De Jesús-Pérez JJ, Protopopova AD, Rocereta JA, Fluck EC, Fricke T, Lee BH, Rohacs T, Leffler A, Moiseenkova-Bell V. Molecular details of ruthenium red pore block in TRPV channels. EMBO Rep 2024; 25:506-523. [PMID: 38225355 PMCID: PMC10897480 DOI: 10.1038/s44319-023-00050-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Revised: 12/19/2023] [Accepted: 12/21/2023] [Indexed: 01/17/2024] Open
Abstract
Transient receptor potential vanilloid (TRPV) channels play a critical role in calcium homeostasis, pain sensation, immunological response, and cancer progression. TRPV channels are blocked by ruthenium red (RR), a universal pore blocker for a wide array of cation channels. Here we use cryo-electron microscopy to reveal the molecular details of RR block in TRPV2 and TRPV5, members of the two TRPV subfamilies. In TRPV2 activated by 2-aminoethoxydiphenyl borate, RR is tightly coordinated in the open selectivity filter, blocking ion flow and preventing channel inactivation. In TRPV5 activated by phosphatidylinositol 4,5-bisphosphate, RR blocks the selectivity filter and closes the lower gate through an interaction with polar residues in the pore vestibule. Together, our results provide a detailed understanding of TRPV subfamily pore block, the dynamic nature of the selectivity filter and allosteric communication between the selectivity filter and lower gate.
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Affiliation(s)
- Ruth A Pumroy
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - José J De Jesús-Pérez
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Anna D Protopopova
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Julia A Rocereta
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Edwin C Fluck
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Tabea Fricke
- Institute for Neurophysiology, Hannover Medical School, 30625, Hannover, Germany
| | - Bo-Hyun Lee
- Department of Physiology and Convergence Medical Science, Institute of Health Sciences, Gyeongsang National University Medical School, Jinju, Korea
- Department of Pharmacology, Physiology and Neuroscience, New Jersey Medical School, Rutgers University, Newark, NJ, 07103, USA
| | - Tibor Rohacs
- Department of Pharmacology, Physiology and Neuroscience, New Jersey Medical School, Rutgers University, Newark, NJ, 07103, USA
| | - Andreas Leffler
- Institute for Neurophysiology, Hannover Medical School, 30625, Hannover, Germany
| | - Vera Moiseenkova-Bell
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
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Li Y, Chang C, Zhu Z, Sun L, Fan C. Terahertz Wave Enhances Permeability of the Voltage-Gated Calcium Channel. J Am Chem Soc 2021; 143:4311-4318. [PMID: 33625851 DOI: 10.1021/jacs.0c09401] [Citation(s) in RCA: 47] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A deficiency of Ca2+ fluxes arising from dysfunctional voltage-gated calcium channels has been associated with a list of calcium channelopathies such as epilepsy, hypokalemic periodic paralysis, episodic ataxia, etc. Apart from analyzing the pathogenic channel mutations, understanding how the channel regulates the ion conduction would be instructive to the treatment as well. In the present work, in relating the free energetics of Ca2+ transport to the calcium channel, we demonstrate the importance of bridging Ca2+ hydration waters, which form hydrogen bonds with channel -COO- and -C═O groups and enable a long-distance effect on the Ca2+ permeation. By firing a terahertz wave which resonates with the stretching mode of either the -COO- or the -C═O group, we obtain significantly enhanced selectivity and conductance of Ca2+. The Ca2+ free energy negatively grows nearly 5-fold. The direct evidence is the reinforced hydrogen bonds. In addition, thanks to forced vibrations, -COO- contributes to raised permeation as well even under a field in resonance with -C═O, and vice versa. Since the resonant terahertz field could manipulate the conduction of calcium channels, it has potential applications in therapeutic intervention such as rectifying a Ca2+ deficiency in degraded calcium channels, inducing apoptosis of tumor cells with overloaded calcium etc.
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Affiliation(s)
- Yangmei Li
- Innovation Laboratory of Terahertz Biophysics, National Innovation Institute of Defense Technology, Beijing 100071, People's Republic of China
| | - Chao Chang
- Innovation Laboratory of Terahertz Biophysics, National Innovation Institute of Defense Technology, Beijing 100071, People's Republic of China.,Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
| | - Zhi Zhu
- School of Optical-Electrical Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, People's Republic of China
| | - Lan Sun
- Innovation Laboratory of Terahertz Biophysics, National Innovation Institute of Defense Technology, Beijing 100071, People's Republic of China
| | - Chunhai Fan
- School of Chemistry and Chemical Engineering, and Institute of Molecular Medicine, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
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3
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Guardiani C, Fedorenko OA, Khovanov IA, Roberts SK. Different roles for aspartates and glutamates for cation permeation in bacterial sodium channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1861:495-503. [PMID: 30529079 DOI: 10.1016/j.bbamem.2018.11.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Revised: 11/16/2018] [Accepted: 11/30/2018] [Indexed: 12/21/2022]
Abstract
A key driving force for ion channel selectivity is represented by the negative charge of the Selectivity Filter carried by aspartate (D) and glutamate (E) residues. However, the structural effects and specific properties of D and E residues have not been extensively studied. In order to investigate this issue we studied the mutants of NaChBac channel with all possible combinations of D and E in the charged rings in position 191 and 192. Electrophysiological measurements showed significant Ca2+ currents only when position 191 was occupied by E. Equilibrium Molecular Dynamics simulations revealed the existence of two binding sites, corresponding to the charged rings and another one, more internal, at the level of L190. The simulations showed that the ion in the innermost site can interact with the residue in position 191 only when this is glutamate. Based on the MD simulations, we suggest that a D in position 191 leads to a high affinity Ca2+ block site resulting from a significant drop in the free energy of binding for an ion moving between the binding sites; in contrast, the free energy change is more gradual when an E residue occupies position 191, resulting in Ca2+ permeability. This scenario is consistent with the model of ion channel selectivity through stepwise changes in binding affinity proposed by Dang and McCleskey. Our study also highlights the importance of the structure of the selectivity filter which should contribute to the development of more detailed physical models for ion channel selectivity.
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Affiliation(s)
- Carlo Guardiani
- School of Engineering, University of Warwick, Coventry CV4 7AL, United Kingdom; Department of Physics, University of Lancaster, Lancaster LA1 4YB, United Kingdom.
| | - Olena A Fedorenko
- Division of Biomedical and Life Sciences, Lancaster University, Lancaster, United Kingdom; School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, United Kingdom
| | - Igor A Khovanov
- School of Engineering, University of Warwick, Coventry CV4 7AL, United Kingdom; Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Stephen K Roberts
- Division of Biomedical and Life Sciences, Lancaster University, Lancaster, United Kingdom.
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4
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Thévenod F, Wolff NA. Iron transport in the kidney: implications for physiology and cadmium nephrotoxicity. Metallomics 2016; 8:17-42. [PMID: 26485516 DOI: 10.1039/c5mt00215j] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The kidney has recently emerged as an organ with a significant role in systemic iron (Fe) homeostasis. Substantial amounts of Fe are filtered by the kidney, which have to be reabsorbed to prevent Fe deficiency. Accordingly Fe transporters and receptors for protein-bound Fe are expressed in the nephron that may also function as entry pathways for toxic metals, such as cadmium (Cd), by way of "ionic and molecular mimicry". Similarities, but also differences in handling of Cd by these transport routes offer rationales for the propensity of the kidney to develop Cd toxicity. This critical review provides a comprehensive update on Fe transport by the kidney and its relevance for physiology and Cd nephrotoxicity. Based on quantitative considerations, we have also estimated the in vivo relevance of the described transport pathways for physiology and toxicology. Under physiological conditions all segments of the kidney tubules are likely to utilize Fe for cellular Fe requiring processes for metabolic purposes and also to contribute to reabsorption of free and bound forms of Fe into the circulation. But Cd entering tubule cells disrupts metabolic pathways and is unable to exit. Furthermore, our quantitative analyses contest established models linking chronic Cd nephrotoxicity to proximal tubular uptake of metallothionein-bound Cd. Hence, Fe transport by the kidney may be beneficial by preventing losses from the body. But increased uptake of Fe or Cd that cannot exit tubule cells may lead to kidney injury, and Fe deficiency may facilitate renal Cd uptake.
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Affiliation(s)
- Frank Thévenod
- Institute of Physiology, Pathophysiology & Toxicology, Center for Biomedical Training and Research (ZBAF), University of Witten/Herdecke, Stockumer Str. 12, 58453 Witten, Germany.
| | - Natascha A Wolff
- Institute of Physiology, Pathophysiology & Toxicology, Center for Biomedical Training and Research (ZBAF), University of Witten/Herdecke, Stockumer Str. 12, 58453 Witten, Germany.
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Voltage-gated calcium channels: Determinants of channel function and modulation by inorganic cations. Prog Neurobiol 2015; 129:1-36. [PMID: 25817891 DOI: 10.1016/j.pneurobio.2014.12.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Revised: 12/15/2014] [Accepted: 12/27/2014] [Indexed: 11/20/2022]
Abstract
Voltage-gated calcium channels (VGCCs) represent a key link between electrical signals and non-electrical processes, such as contraction, secretion and transcription. Evolved to achieve high rates of Ca(2+)-selective flux, they possess an elaborate mechanism for selection of Ca(2+) over foreign ions. It has been convincingly linked to competitive binding in the pore, but the fundamental question of how this is reconcilable with high rates of Ca(2+) transfer remains unanswered. By virtue of their similarity to Ca(2+), polyvalent cations can interfere with the function of VGCCs and have proven instrumental in probing the mechanisms underlying selective permeation. Recent emergence of crystallographic data on a set of Ca(2+)-selective model channels provides a structural framework for permeation in VGCCs, and warrants a reconsideration of their diverse modulation by polyvalent cations, which can be roughly separated into three general mechanisms: (I) long-range interactions with charged regions on the surface, affecting the local potential sensed by the channel or influencing voltage-sensor movement by repulsive forces (electrostatic effects), (II) short-range interactions with sites in the ion-conducting pathway, leading to physical obstruction of the channel (pore block), and in some cases (III) short-range interactions with extracellular binding sites, leading to non-electrostatic modifications of channel gating (allosteric effects). These effects, together with the underlying molecular modifications, provide valuable insights into the function of VGCCs, and have important physiological and pathophysiological implications. Allosteric suppression of some of the pore-forming Cavα1-subunits (Cav2.3, Cav3.2) by Zn(2+) and Cu(2+) may play a major role for the regulation of excitability by endogenous transition metal ions. The fact that these ions can often traverse VGCCs can contribute to the detrimental intracellular accumulation of metal ions following excessive release of endogenous Cu(2+) and Zn(2+) or exposure to non-physiological toxic metal ions.
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Buraei Z, Lee HK, Elmslie KS. Single channel measurements demonstrate the voltage dependence of permeation through N-type and L-type CaV channels. Channels (Austin) 2015; 9:50-5. [PMID: 25664681 DOI: 10.4161/19336950.2014.991606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The delivery of Ca2+ into cells by CaV channels provides the trigger for many cellular actions, such as cardiac muscle contraction and neurotransmitter release. Thus, a full understanding of Ca2+ permeation through these channels is critical. Using whole-cell voltage-clamp recordings, we recently demonstrated that voltage modulates the apparent affinity of N-type (CaV2.2) channels for permeating Ca2+ and Ba2+ ions. While we took many steps to ensure the high fidelity of our recordings, problems can occur when CaV currents become large and fast, or when currents run down. Thus, we use here single channel recordings to further test the hypothesis that permeating ions interact with N-type channels in a voltage-dependent manner. We also examined L-type (CaV1.2) channels to determine if these channels also exhibit voltage-dependent permeation. Like our whole-cell data, we find that voltage modulates N-channel affinity for Ba2+ at voltages>0 mV, but has little or no effect at voltages<0 mV. Furthermore, we demonstrate that permeation through L-channel is also modulated by voltage. Thus, voltage-dependence may be a common feature of divalent cation permeation through CaV1 and CaV2 channels (i.e. high-voltage activated CaV channels). The voltage dependence of CaV1 channel permeation is likely a mechanism mediating sustained Ca2+ influx during the plateau phase of the cardiac action potential.
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Affiliation(s)
- Zafir Buraei
- a Department of Biology ; Pace University ; New York , NY USA
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Buraei Z, Liang H, Elmslie KS. Voltage control of Ca²⁺ permeation through N-type calcium (Ca(V)2.2) channels. ACTA ACUST UNITED AC 2014; 144:207-20. [PMID: 25114024 PMCID: PMC4144670 DOI: 10.1085/jgp.201411201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Voltage dependence of permeation enhances Ca2+ influx through CaV2.2 channels relative to that of other ions at depolarized voltages. Voltage-gated calcium (CaV) channels deliver Ca2+ to trigger cellular functions ranging from cardiac muscle contraction to neurotransmitter release. The mechanism by which these channels select for Ca2+ over other cations is thought to involve multiple Ca2+-binding sites within the pore. Although the Ca2+ affinity and cation preference of these sites have been extensively investigated, the effect of voltage on these sites has not received the same attention. We used a neuronal preparation enriched for N-type calcium (CaV2.2) channels to investigate the effect of voltage on Ca2+ flux. We found that the EC50 for Ca2+ permeation increases from 13 mM at 0 mV to 240 mM at 60 mV, indicating that, during permeation, Ca2+ ions sense the electric field. These data were nicely reproduced using a three-binding-site step model. Using roscovitine to slow CaV2.2 channel deactivation, we extended these measurements to voltages <0 mV. Permeation was minimally affected at these hyperpolarized voltages, as was predicted by the model. As an independent test of voltage effects on permeation, we examined the Ca2+-Ba2+ anomalous mole fraction (MF) effect, which was both concentration and voltage dependent. However, the Ca2+-Ba2+ anomalous MF data could not be reproduced unless we added a fourth site to our model. Thus, Ca2+ permeation through CaV2.2 channels may require at least four Ca2+-binding sites. Finally, our results suggest that the high affinity of Ca2+ for the channel helps to enhance Ca2+ influx at depolarized voltages relative to other ions (e.g., Ba2+ or Na+), whereas the absence of voltage effects at negative potentials prevents Ca2+ from becoming a channel blocker. Both effects are needed to maximize Ca2+ influx over the voltages spanned by action potentials.
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Affiliation(s)
- Zafir Buraei
- Department of Biology and Health Sciences, Pace University, New York, NY 10038 Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA 70112
| | - Haoya Liang
- Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA 70112
| | - Keith S Elmslie
- Department of Physiology, Tulane University Health Sciences Center, New Orleans, LA 70112 The Baker Laboratory of Pharmacology, Department of Pharmacology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, Kirksville, MO 63501
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8
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Models of calcium permeation through T-type channels. Pflugers Arch 2014; 466:635-44. [DOI: 10.1007/s00424-013-1437-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Revised: 12/27/2013] [Accepted: 12/28/2013] [Indexed: 12/19/2022]
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9
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Contribution of different Ca2+ channels to the acrosome reaction-mediated initiation of sperm motility in the newt Cynops pyrrhogaster. ZYGOTE 2013; 23:342-51. [DOI: 10.1017/s0967199413000609] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
SummaryInitiation of sperm motility in urodeles, which is induced by a sperm motility-initiating substance (SMIS) in the sequestered granules on the surface of egg jelly, is mediated by the acrosome reaction (AR), which is triggered by an AR-inducing substance (ARIS) on a sheet-like structure. Details of the unique process of the interaction between egg jelly and sperm in these species is still unclear. The current study showed the fine structure of egg jelly in the newt Cynops pyrrhogaster, a urodele species, revealing that its outer surface was covered by a sheet-like structure of approximately 0.29 μm in thickness. Granules of approximately 2 μm in diameter with small particles of approximately 54 nm were attached to its surface and distributed inhomogeneously just beneath the sheet-like structure. Emission spectrometry revealed that the Ca2+ concentration was maintained at a high level compared with that of the blood plasma and the vas deferens fluid, suggesting that egg jelly is a reliable source of Ca2+ for the sperm–egg interaction. Blockers of the T-type voltage-dependent Ca2+ channel (VDCC), but not the L-type VDCC, inhibited both AR and initiation of sperm motility. Conversely, Ni+, which affects the α1 H subunit of T-type VDCC, only inhibited the initiation of sperm motility. These data suggest that, in response to ARIS and SMIS, sequential gating of distinct Ca2+ channels occurs in the AR, followed by the initiation of sperm motility on the surface of the egg jelly in C. pyrrhogaster at fertilization.
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Tang L, Gamal El-Din TM, Payandeh J, Martinez GQ, Heard TM, Scheuer T, Zheng N, Catterall WA. Structural basis for Ca2+ selectivity of a voltage-gated calcium channel. Nature 2013; 505:56-61. [PMID: 24270805 PMCID: PMC3877713 DOI: 10.1038/nature12775] [Citation(s) in RCA: 230] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Accepted: 10/09/2013] [Indexed: 12/12/2022]
Abstract
Voltage-gated calcium (CaV) channels catalyze rapid, highly selective influx of Ca2+ into cells despite 70-fold higher extracellular concentration of Na+. How CaV channels solve this fundamental biophysical problem remains unclear. Here we report physiological and crystallographic analyses of a calcium selectivity filter constructed in the homotetrameric bacterial NaV channel NaVAb. Our results reveal interactions of hydrated Ca2+ with two high-affinity Ca2+-binding sites followed by a third lower-affinity site that would coordinate Ca2+ as it moves inward. At the selectivity filter entry, Site 1 is formed by four carboxyl side-chains, which play a critical role in determining Ca2+ selectivity. Four carboxyls plus four backbone carbonyls form Site 2, which is targeted by the blocking cations, Cd2+ and Mn2+, with single occupancy. The lower-affinity Site 3 is formed by four backbone carbonyls alone, which mediate exit into the central cavity. This pore architecture suggests a conduction pathway involving transitions between two main states with one or two hydrated Ca2+ ions bound in the selectivity filter and supports a “knock-off” mechanism of ion permeation through a stepwise-binding process. The multi-ion selectivity filter of our CaVAb model establishes a structural framework for understanding mechanisms of ion selectivity and conductance by vertebrate CaV channels.
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Affiliation(s)
- Lin Tang
- 1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2] Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, USA [3]
| | - Tamer M Gamal El-Din
- 1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2]
| | - Jian Payandeh
- 1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2] Department of Structural Biology, Genentech Inc., South San Francisco, California 94080, USA
| | - Gilbert Q Martinez
- Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA
| | - Teresa M Heard
- Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA
| | - Todd Scheuer
- Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA
| | - Ning Zheng
- 1] Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA [2] Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, USA
| | - William A Catterall
- Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA
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11
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Lopin KV, Gray IP, Obejero-Paz CA, Thévenod F, Jones SW. Fe²⁺ block and permeation of CaV3.1 (α1G) T-type calcium channels: candidate mechanism for non-transferrin-mediated Fe²⁺ influx. Mol Pharmacol 2012; 82:1194-204. [PMID: 22973060 DOI: 10.1124/mol.112.080184] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Iron is a biologically essential metal, but excess iron can cause damage to the cardiovascular and nervous systems. We examined the effects of extracellular Fe²⁺ on permeation and gating of Ca(V)3.1 channels stably transfected in HEK293 cells, by using whole-cell recording. Precautions were taken to maintain iron in the Fe²⁺ state (e.g., use of extracellular ascorbate). With the use of instantaneous I-V currents (measured after strong depolarization) to isolate the effects on permeation, extracellular Fe²⁺ rapidly blocked currents with 2 mM extracellular Ca²⁺ in a voltage-dependent manner, as described by a Woodhull model with K(D) = 2.5 mM at 0 mV and apparent electrical distance δ = 0.17. Extracellular Fe²⁺ also shifted activation to more-depolarized voltages (by ∼10 mV with 1.8 mM extracellular Fe²⁺) somewhat more strongly than did extracellular Ca²⁺ or Mg²⁺, which is consistent with a Gouy-Chapman-Stern model with surface charge density σ = 1 e(-)/98 Ų and K(Fe) = 4.5 M⁻¹ for extracellular Fe²⁺. In the absence of extracellular Ca²⁺ (and with extracellular Na⁺ replaced by TEA), Fe²⁺ carried detectable, whole-cell, inward currents at millimolar concentrations (73 ± 7 pA at -60 mV with 10 mM extracellular Fe²⁺). With a two-site/three-barrier Eyring model for permeation of Ca(V)3.1 channels, we estimated a transport rate for Fe²⁺ of ∼20 ions/s for each open channel at -60 mV and pH 7.2, with 1 μM extracellular Fe²⁺ (with 2 mM extracellular Ca²⁺). Because Ca(V)3.1 channels exhibit a significant "window current" at that voltage (open probability, ∼1%), Ca(V)3.1 channels represent a likely pathway for Fe²⁺ entry into cells with clinically relevant concentrations of extracellular Fe²⁺.
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Affiliation(s)
- Kyle V Lopin
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA
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12
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Lopin KV, Thévenod F, Page JC, Jones SW. Cd²⁺ block and permeation of CaV3.1 (α1G) T-type calcium channels: candidate mechanism for Cd²⁺ influx. Mol Pharmacol 2012; 82:1183-93. [PMID: 22973059 DOI: 10.1124/mol.112.080176] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Cd²⁺ is an industrial pollutant that can cause cytotoxicity in multiple organs. We examined the effects of extracellular Cd²⁺ on permeation and gating of Ca(v)3.1 (α1G) channels stably transfected in HEK293 cells, by using whole-cell recording. With the use of instantaneous I-V currents (measured after strong depolarization) to isolate the effects on permeation, Cd²⁺ rapidly blocked currents with 2 mM Ca²⁺ in a voltage-dependent manner. The block caused by Cd²⁺ was relieved at more-hyperpolarized potentials, which suggests that Cd²⁺ can permeate through the selectivity filter of the channel into the cytosol. In the absence of other permeant ions (Ca²⁺ and Na⁺ replaced by N-methyl-d-glucamine), Cd²⁺ carried sizable inward currents through Ca(v)3.1 channels (210 ± 20 pA at -60 mV with 2 mM Cd²⁺). Ca(v)3.1 channels have a significant "window current" at that voltage (open probability, ∼1%), which makes them a candidate pathway for Cd²⁺ entry into cells during Cd²⁺ exposure. Incubation with radiolabeled ¹⁰⁹Cd²⁺ confirmed uptake of Cd²⁺ into cells with Ca(v)3.1 channels.
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Affiliation(s)
- Kyle V Lopin
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA
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