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Hung TY, Wu SN, Huang CW. Safinamide, an inhibitor of monoamine oxidase, modulates the magnitude, gating, and hysteresis of sodium ion current. BMC Pharmacol Toxicol 2024; 25:17. [PMID: 38331833 PMCID: PMC10851555 DOI: 10.1186/s40360-024-00739-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Accepted: 01/30/2024] [Indexed: 02/10/2024] Open
Abstract
BACKGROUND Safinamide (SAF), an α-aminoamide derivative and a selective, reversible monoamine oxidase (MAO)-B inhibitor, has both dopaminergic and nondopaminergic (glutamatergic) properties. Several studies have explored the potential of SAF against various neurological disorders; however, to what extent SAF modulates the magnitude, gating, and voltage-dependent hysteresis [Hys(V)] of ionic currents remains unknown. METHODS With the aid of patch-clamp technology, we investigated the effects of SAF on voltage-gated sodium ion (NaV) channels in pituitary GH3 cells. RESULTS SAF concentration-dependently stimulated the transient (peak) and late (sustained) components of voltage-gated sodium ion current (INa) in pituitary GH3 cells. The conductance-voltage relationship of transient INa [INa(T)] was shifted to more negative potentials with the SAF presence; however, the steady-state inactivation curve of INa(T) was shifted in a rightward direction in its existence. SAF increased the decaying time constant of INa(T) induced by a train of depolarizing stimuli. Notably, subsequent addition of ranolazine or mirogabalin reversed the SAF-induced increase in the decaying time constant. SAF also increased the magnitude of window INa induced by an ascending ramp voltage Vramp. Furthermore, SAF enhanced the Hys(V) behavior of persistent INa induced by an upright isosceles-triangular Vramp. Single-channel cell-attached recordings indicated SAF effectively increased the open-state probability of NaV channels. Molecular docking revealed SAF interacts with both MAO and NaV channels. CONCLUSION SAF may interact directly with NaV channels in pituitary neuroendocrine cells, modulating membrane excitability.
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Affiliation(s)
- Te-Yu Hung
- Department of Pediatrics, Chi-Mei Medical Center, Tainan, Taiwan
| | - Sheng-Nan Wu
- Department of Physiology, National Cheng Kung University Medical College, Tainan, Taiwan.
- Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan, Taiwan.
- School of Medicine, National Sun Yat-sen University, Kaohsiung, Taiwan.
| | - Chin-Wei Huang
- Department of Neurology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
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Hung TY, Wu SN, Huang CW. Concerted suppressive effects of carisbamate, an anti-epileptic alkyl-carbamate drug, on voltage-gated Na + and hyperpolarization-activated cation currents. Front Cell Neurosci 2023; 17:1159067. [PMID: 37293624 PMCID: PMC10244622 DOI: 10.3389/fncel.2023.1159067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 05/02/2023] [Indexed: 06/10/2023] Open
Abstract
Carisbamate (CRS, RWJ-333369) is a new anti-seizure medication. It remains unclear whether and how CRS can perturb the magnitude and/or gating kinetics of membrane ionic currents, despite a few reports demonstrating its ability to suppress voltage-gated Na+ currents. In this study, we observed a set of whole-cell current recordings and found that CRS effectively suppressed the voltage-gated Na+ (INa) and hyperpolarization-activated cation currents (Ih) intrinsically in electrically excitable cells (GH3 cells). The effective IC50 values of CRS for the differential suppression of transient (INa(T)) and late INa (INa(L)) were 56.4 and 11.4 μM, respectively. However, CRS strongly decreased the strength (i.e., Δarea) of the nonlinear window component of INa (INa(W)), which was activated by a short ascending ramp voltage (Vramp); the subsequent addition of deltamethrin (DLT, 10 μM) counteracted the ability of CRS (100 μM, continuous exposure) to suppress INa(W). CRS strikingly decreased the decay time constant of INa(T) evoked during pulse train stimulation; however, the addition of telmisartan (10 μM) effectively attenuated the CRS (30 μM, continuous exposure)-mediated decrease in the decay time constant of the current. During continued exposure to deltamethrin (10 μM), known to be a pyrethroid insecticide, the addition of CRS resulted in differential suppression of the amplitudes of INa(T) and INa(L). The amplitude of Ih activated by a 2-s membrane hyperpolarization was diminished by CRS in a concentration-dependent manner, with an IC50 value of 38 μM. For Ih, CRS altered the steady-state I-V relationship and attenuated the strength of voltage-dependent hysteresis (Hys(V)) activated by an inverted isosceles-triangular Vramp. Moreover, the addition of oxaliplatin effectively reversed the CRS-mediated suppression of Hys(V). The predicted docking interaction between CRS and with a model of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel or between CRS and the hNaV1.7 channel reflects the ability of CRS to bind to amino acid residues in HCN or hNaV1.7 channel via hydrogen bonds and hydrophobic interactions. These findings reveal the propensity of CRS to modify INa(T) and INa(L) differentially and to effectively suppress the magnitude of Ih. INa and Ih are thus potential targets of the actions of CRS in terms of modulating cellular excitability.
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Affiliation(s)
- Te-Yu Hung
- Department of Pediatrics, Chi Mei Medical Center, Tainan, Taiwan
| | - Sheng-Nan Wu
- Department of Physiology, College of Medicine, National Cheng Kung University, Tainan, Taiwan
- College of Medicine, Institute of Basic Medical Sciences, National Cheng Kung University, Tainan, Taiwan
- School of Medicine, College of Medicine, National Sun Yat-sen University, Kaohsiung City, Taiwan
| | - Chin-Wei Huang
- Department of Neurology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan
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Inhibition of Voltage-Gated Na + Currents Exerted by KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea), an Inhibitor of Na +-Ca 2+ Exchanging Process. Int J Mol Sci 2023; 24:ijms24021805. [PMID: 36675319 PMCID: PMC9864174 DOI: 10.3390/ijms24021805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 12/21/2022] [Accepted: 01/13/2023] [Indexed: 01/18/2023] Open
Abstract
KB-R7943, an isothiourea derivative, has been recognized as an inhibitor in the reverse mode of the Na+-Ca2+ exchanging process. This compound was demonstrated to prevent intracellular Na+-dependent Ca2+ uptake in intact cells; however, it is much less effective at preventing extracellular Na+-dependent Ca2+ efflux. Therefore, whether or how this compound may produce any perturbations on other types of ionic currents, particularly on voltage-gated Na+ current (INa), needs to be further studied. In this study, the whole-cell current recordings demonstrated that upon abrupt depolarization in pituitary GH3 cells, the exposure to KB-R7943 concentration-dependently depressed the transient (INa(T)) or late component (INa(L)) of INa with an IC50 value of 11 or 0.9 μM, respectively. Likewise, the dissociation constant for the KB-R7943-mediated block of INa on the basis of a minimum reaction scheme was estimated to be 0.97 μM. The presence of benzamil or amiloride could suppress the INa(L) magnitude. The instantaneous window Na+ current (INa(W)) activated by abrupt ascending ramp voltage (Vramp) was suppressed by adding KB-R7943; however, subsequent addition of deltamethrin or tefluthrin (Tef) effectively reversed KB-R7943-inhibted INa(W). With prolonged duration of depolarizing pulses, the INa(L) amplitude became exponentially decreased; moreover, KB-R7943 diminished INa(L) magnitude. The resurgent Na+ current (INa(R)) evoked by a repolarizing Vramp was also suppressed by adding this compound; moreover, subsequent addition of ranolazine or Tef further diminished or reversed, respectively, its reduction in INa(R) magnitude. The persistent Na+ current (INa(P)) activated by sinusoidal voltage waveform became enhanced by Tef; however, subsequent application of KB-R7943 counteracted Tef-stimulated INa(P). The docking prediction reflected that there seem to be molecular interactions of this molecule with the hNaV1.2 or hNaV1.7 channels. Collectively, this study highlights evidence showing that KB-R7943 has the propensity to perturb the magnitude and gating kinetics of INa (e.g., INa(T), INa(L), INa(W), INa(R), and INa(P)) and that the NaV channels appear to be important targets for the in vivo actions of KB-R7943 or other relevant compounds.
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Ballarini E, Malacrida A, Rodriguez-Menendez V, Pozzi E, Canta A, Chiorazzi A, Monza L, Semperboni S, Meregalli C, Carozzi VA, Hashemi M, Nicolini G, Scuteri A, Housley SN, Cavaletti G, Alberti P. Sodium-Calcium Exchanger 2: A Pivotal Role in Oxaliplatin Induced Peripheral Neurotoxicity and Axonal Damage? Int J Mol Sci 2022; 23:10063. [PMID: 36077454 PMCID: PMC9456447 DOI: 10.3390/ijms231710063] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 08/26/2022] [Accepted: 08/29/2022] [Indexed: 12/14/2022] Open
Abstract
Oxaliplatin (OHP)-induced peripheral neurotoxicity (OIPN) is a frequent adverse event of colorectal cancer treatment. OIPN encompasses a chronic and an acute syndrome. The latter consists of transient axonal hyperexcitability, due to unbalance in Na+ voltage-operated channels (Na+VOC). This leads to sustained depolarisation which can activate the reverse mode of the Na+/Ca2+ exchanger 2 (NCX2), resulting in toxic Ca2+ accumulation and axonal damage (ADa). We explored the role of NCX2 in in vitro and in vivo settings. Embryonic rat Dorsal Root Ganglia (DRG) organotypic cultures treated with SEA0400 (SEA), a NCX inhibitor, were used to assess neuroprotection in a proof-of-concept and pilot study to exploit NCX modulation to prevent ADa. In vivo, OHP treated mice (7 mg/Kg, i.v., once a week for 8 weeks) were compared with a vehicle-treated group (n = 12 each). Neurophysiological and behavioural testing were performed to characterise acute and chronic OIPN, and morphological analyses were performed to detect ADa. Immunohistochemistry, immunofluorescence, and western blotting (WB) analyses were also performed to demonstrate changes in NCX2 immunoreactivity and protein expression. In vitro, NCX inhibition was matched by ADa mitigation. In the in vivo part, after verifyingboth acute and chronic OIPN had ensued, we confirmed via immunohistochemistry, immunofluorescence, and WB that a significant NCX2 alteration had ensued in the OHP group. Our data suggest NCX2 involvement in ADa development, paving the way to a new line of research to prevent OIPN.
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Affiliation(s)
- Elisa Ballarini
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Alessio Malacrida
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Virginia Rodriguez-Menendez
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Eleonora Pozzi
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Annalisa Canta
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Alessia Chiorazzi
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Laura Monza
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Sara Semperboni
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Cristina Meregalli
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Valentina Alda Carozzi
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Maryamsadat Hashemi
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Gabriella Nicolini
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Arianna Scuteri
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Stephen N. Housley
- Integrated Cancer Research Center, School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Guido Cavaletti
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
| | - Paola Alberti
- School of Medicine and Surgery, University of Milano-Bicocca, 20126 Milan, Italy
- NeuroMI (Milan Center for Neuroscience), 20126 Milan, Italy
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Characterization in Inhibitory Effectiveness of Carbamazepine in Voltage-Gated Na + and Erg-Mediated K + Currents in a Mouse Neural Crest-Derived (Neuro-2a) Cell Line. Int J Mol Sci 2022; 23:ijms23147892. [PMID: 35887240 PMCID: PMC9321339 DOI: 10.3390/ijms23147892] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 07/15/2022] [Accepted: 07/15/2022] [Indexed: 12/18/2022] Open
Abstract
Carbamazepine (CBZ, Tegretol®) is an anticonvulsant used in the treatment of epilepsy and neuropathic pain; however, several unwanted effects of this drug have been noticed. Therefore, the regulatory actions of CBZ on ionic currents in electrically excitable cells need to be reappraised, although its efficacy in suppressing voltage-gated Na+ current (INa) has been disclosed. This study was undertaken to explore the modifications produced by CBZ on ionic currents (e.g., INa and erg-mediated K+ current [IK(erg)]) measured from Neuro-2a (N2a) cells. In these cells, we found that this drug differentially suppressed the peak (transient, INa(T)) and sustained (late, INa(L)) components of INa in a concentration-dependent manner with effective IC50 of 56 and 18 μM, respectively. The overall current–voltage relationship of INa(T) with or without the addition of CBZ remained unchanged; however, the strength (i.e., ∆area) in the window component of INa (INa(W)) evoked by the short ascending ramp pulse (Vramp) was overly lessened in the CBZ presence. Tefluthrin (Tef), a synthetic pyrethroid, known to stimulate INa, augmented the strength of the voltage-dependent hysteresis (Hys(V)) of persistent INa (INa(P)) in response to the isosceles-triangular Vramp; moreover, further application of CBZ attenuated Tef-mediated accentuation of INa(P)’s Hys(V). With a two-step voltage protocol, the recovery of INa(T) inactivation seen in Neuro-2a cells became progressively slowed by adding CBZ; however, the cumulative inhibition of INa(T) evoked by pulse train stimulation was enhanced during exposure to this drug. Neuro-2a-cell exposure to CBZ (100 μM), the magnitude of erg-mediated K+ current measured throughout the entire voltage-clamp steps applied was mildly inhibited. The docking results regarding the interaction of CBZ and voltage-gate Na+ (NaV) channel predicted the ability of CBZ to bind to some amino-acid residues in NaV due to the existence of a hydrogen bond or hydrophobic contact. It is conceivable from the current investigations that the INa (INa(T), INa(L), INa(W), and INa(P)) residing in Neuro-2a cells are susceptible to being suppressed by CBZ, and that its block on INa(L) is larger than that on INa(T). Collectively, the magnitude and gating of NaV channels produced by the CBZ presence might have an impact on its anticonvulsant and analgesic effects occurring in vivo.
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The Evidence for Effective Inhibition of INa Produced by Mirogabalin ((1R,5S,6S)-6-(aminomethyl)-3-ethyl-bicyclo [3.2.0] hept-3-ene-6-acetic acid), a Known Blocker of Ca V Channels. Int J Mol Sci 2022; 23:ijms23073845. [PMID: 35409204 PMCID: PMC8998350 DOI: 10.3390/ijms23073845] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 03/28/2022] [Accepted: 03/29/2022] [Indexed: 01/27/2023] Open
Abstract
Mirogabalin (MGB, Tarlige®), an inhibitor of the α2δ-1 subunit of voltage-gated Ca2+ (CaV) channels, is used as a way to alleviate peripheral neuropathic pain and diabetic neuropathy. However, to what extent MGB modifies the magnitude, gating, and/or hysteresis of various types of plasmalemmal ionic currents remains largely unexplored. In pituitary tumor (GH3) cells, we found that MGB was effective at suppressing the peak (transient, INa(T)) and sustained (late, INa(L)) components of the voltage-gated Na+ current (INa) in a concentration-dependent manner, with an effective IC50 of 19.5 and 7.3 μM, respectively, while the KD value calculated on the basis of minimum reaction scheme was 8.2 μM. The recovery of INa(T) inactivation slowed in the presence of MGB, although the overall current-voltage relation of INa(T) was unaltered; however, there was a leftward shift in the inactivation curve of the current. The magnitude of the window (INa(W)) or resurgent INa (INa(R)) evoked by the respective ascending or descending ramp pulse (Vramp) was reduced during cell exposure to MGB. MGB-induced attenuation in INa(W) or INa(R) was reversed by the further addition of tefluthrin, a pyrethroid insecticide known to stimulate INa. MGB also effectively lessened the strength of voltage-dependent hysteresis of persistent INa in response to the isosceles triangular Vramp. The cumulative inhibition of INa(T), evoked by pulse train stimulation, was enhanced in its presence. Taken together, in addition to the inhibition of CaV channels, the NaV channel attenuation produced by MGB might have an impact in its analgesic effects occurring in vivo.
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Cho HY, Chen PC, Chuang TH, Yu MC, Wu SN. Activation of Voltage-Gated Na+ Current by GV-58, a Known Activator of CaV Channels. Biomedicines 2022; 10:biomedicines10030721. [PMID: 35327523 PMCID: PMC8945347 DOI: 10.3390/biomedicines10030721] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 03/10/2022] [Accepted: 03/17/2022] [Indexed: 02/04/2023] Open
Abstract
GV-58 ((2R)-2-[(6-{[(5-methylthiophen-2-yl)methyl]amino}-9-propyl-9H-purin-2-yl)amino]butan-1-ol) is recognized to be an activator of N- and P/Q-type Ca2+ currents. However, its modulatory actions on other types of ionic currents in electrically excitable cells remain largely unanswered. This study was undertaken to explore the possible modifications caused by GV-58 in ionic currents (e.g., voltage-gated Na+ current [INa], A-type K+ current [IK(A)], and erg-mediated K+ current [IK(erg)]) identified from pituitary GH3 lactotrophs. GH3 cell exposure to GV-58 enhanced the transient and late components of INa with varying potencies; consequently, the EC50 values of GV-58 required for its differential increase in peak and late INa in GH3 cells were estimated to be 8.9 and 2.6 μM, respectively. The INa in response to brief depolarizing pulse was respectively stimulated or suppressed by GV-58 or tetrodotoxin, but it failed to be altered by ω-conotoxin MVIID. Cell exposure to this compound increased the recovery of INa inactivation evoked by two-pulse protocol based on a geometrics progression; however, in its presence, there was a slowing in the inactivation rate of current decay evoked by a train of depolarizing pulses. The existence of GV-58 also resulted in an increase in the amplitude of ramp-induced resurgent and window INa. The presence of this compound inhibited IK(A) magnitude, accompanied by a shortening in inactivation time course of the current; however, it mildly decreased IK(erg). Under current-clamp conditions, GV-58 increased the frequency of spontaneous action potentials in GH3 cells. Moreover, in NSC-34 motor neuron-like cells, the presence of GV-58 not only raised INa amplitude but also reduced current inactivation. Taken together, the overall work provides a noticeable yet unidentified finding which implies that, in addition to its agonistic effect on Ca2+ currents, GV-58 may concertedly modify the amplitude and gating kinetics of INa in electrically excitable cells, hence modifiying functional activities in these cells.
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Affiliation(s)
- Hsin-Yen Cho
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
| | - Pei-Chun Chen
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
- Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan City 70101, Taiwan
| | - Tzu-Hsien Chuang
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
| | - Meng-Cheng Yu
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
| | - Sheng-Nan Wu
- Department of Physiology, National Cheng Kung University Medical College, Tainan City 70101, Taiwan; (H.-Y.C.); (P.-C.C.); (T.-H.C.); (M.-C.Y.)
- Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan City 70101, Taiwan
- Correspondence: ; Tel.: +886-6-2353535-5334; Fax: +886-6-2362780
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Morris CE, Wheeler JJ, Joos B. The Donnan-dominated resting state of skeletal muscle fibers contributes to resilience and longevity in dystrophic fibers. J Gen Physiol 2022; 154:212743. [PMID: 34731883 PMCID: PMC8570295 DOI: 10.1085/jgp.202112914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 09/30/2021] [Indexed: 11/28/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is an X-linked dystrophin-minus muscle-wasting disease. Ion homeostasis in skeletal muscle fibers underperforms as DMD progresses. But though DMD renders these excitable cells intolerant of exertion, sodium overloaded, depolarized, and spontaneously contractile, they can survive for several decades. We show computationally that underpinning this longevity is a strikingly frugal, robust Pump-Leak/Donnan (P-L/D) ion homeostatic process. Unlike neurons, which operate with a costly “Pump-Leak–dominated” ion homeostatic steady state, skeletal muscle fibers operate with a low-cost “Donnan-dominated” ion homeostatic steady state that combines a large chloride permeability with an exceptionally small sodium permeability. Simultaneously, this combination keeps fiber excitability low and minimizes pump expenditures. As mechanically active, long-lived multinucleate cells, skeletal muscle fibers have evolved to handle overexertion, sarcolemmal tears, ischemic bouts, etc.; the frugality of their Donnan dominated steady state lets them maintain the outsized pump reserves that make them resilient during these inevitable transient emergencies. Here, P-L/D model variants challenged with DMD-type insult/injury (low pump-strength, overstimulation, leaky Nav and cation channels) show how chronic “nonosmotic” sodium overload (observed in DMD patients) develops. Profoundly severe DMD ion homeostatic insult/injury causes spontaneous firing (and, consequently, unwanted excitation–contraction coupling) that elicits cytotoxic swelling. Therefore, boosting operational pump-strength and/or diminishing sodium and cation channel leaks should help extend DMD fiber longevity.
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Affiliation(s)
- Catherine E Morris
- Neuroscience, Ottawa Hospital Research Institute, Ottawa, Canada.,Center for Neural Dynamics, University of Ottawa, Ottawa, Canada
| | | | - Béla Joos
- Center for Neural Dynamics, University of Ottawa, Ottawa, Canada.,Department of Physics, University of Ottawa, Ottawa, Canada
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Somayaji MR, Przekwas AJ, Gupta RK. Combination Therapy for Multi-Target Manipulation of Secondary Brain Injury Mechanisms. Curr Neuropharmacol 2018; 16:484-504. [PMID: 28847295 PMCID: PMC6018188 DOI: 10.2174/1570159x15666170828165711] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 02/10/2017] [Accepted: 03/28/2017] [Indexed: 12/14/2022] Open
Abstract
Traumatic brain injury (TBI) is a major healthcare problem that affects millions of people worldwide. Despite advances in understanding and developing preventative and treatment strategies using preclinical animal models, clinical trials to date have failed, and a 'magic bullet' for effectively treating TBI-induced damage does not exist. Thus, novel pharmacological strategies to effectively manipulate the complex and heterogeneous pathophysiology of secondary injury mechanisms are needed. Given that goal, this paper discusses the relevance and advantages of combination therapies (COMTs) for 'multi-target manipulation' of the secondary injury cascade by administering multiple drugs to achieve an optimal therapeutic window of opportunity (e.g., temporally broad window) and compares these regimens to monotherapies that manipulate a single target with a single drug at a given time. Furthermore, we posit that integrated mechanistic multiscale models that combine primary injury biomechanics, secondary injury mechanobiology/neurobiology, physiology, pharmacology and mathematical programming techniques could account for vast differences in the biological space and time scales and help to accelerate drug development, to optimize pharmacological COMT protocols and to improve treatment outcomes.
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Affiliation(s)
| | | | - Raj K. Gupta
- Department of Defense Blast Injury Research Program Coordinating Office, U.S. Army Medical Research and Materiel Command, Fort Detrick, MD, USA
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Joos B, Barlow BM, Morris CE. Calculating the Consequences of Left-Shifted Nav Channel Activity in Sick Excitable Cells. Handb Exp Pharmacol 2017; 246:401-422. [PMID: 29030712 DOI: 10.1007/164_2017_63] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Two features common to diverse sick excitable cells are "leaky" Nav channels and bleb damage-damaged membranes. The bleb damage, we have argued, causes a channel kinetics based "leakiness." Recombinant (node of Ranvier type) Nav1.6 channels voltage-clamped in mechanically-blebbed cell-attached patches undergo a damage intensity dependent kinetic change. Specifically, they experience a coupled hyperpolarizing (left) shift of the activation and inactivation processes. The biophysical observations on Nav1.6 currents formed the basis of Nav-Coupled Left Shift (Nav-CLS) theory. Node of Ranvier excitability can be modeled with Nav-CLS imposed at varying LS intensities and with varying fractions of total nodal membrane affected. Mild damage from which sick excitable cells might recover is of most interest pathologically. Accordingly, Na+/K+ ATPase (pump) activity was included in the modeling. As we described more fully in our other recent reviews, Nav-CLS in nodes with pumps proves sufficient to predict many of the pathological excitability phenomena reported for sick excitable cells. This review explains how the model came about and outlines how we have used it. Briefly, we direct the reader to studies in which Nav-CLS is being implemented in larger scale models of damaged excitable tissue. For those who might find it useful for teaching or research purposes, we coded the Nav-CLS/node of Ranvier model (with pumps) in NEURON. We include, here, the resulting "Regimes" plot of classes of excitability dysfunction.
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Affiliation(s)
- Bela Joos
- Department of Physics, University of Ottawa, Ottawa, ON, Canada.
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Abstract
Sick excitable cells (ie, Nav channel-expressing cells injured by trauma, ischemia, inflammatory, and other conditions) typically exhibit "acquired sodium channelopathies" which, we argue, reflect bleb-damaged membranes rendering their Nav channels "leaky." The situation is excitotoxic because untreated Nav leak exacerbates bleb damage. Fast Nav inactivation (a voltage-independent process) is so tightly coupled, kinetically speaking, to the inherently voltage-dependent process of fast activation that when bleb damage accelerates and thus left-shifts macroscopic fast activation, fast inactivation accelerates to the same extent. The coupled g(V) and availability(V) processes and their window conductance regions consequently left-shift by the same number of millivolts. These damage-induced hyperpolarizing shifts, whose magnitude increases with damage intensity, are called coupled left shift (CLS). Based on past work and modeling, we discuss how to test for Nav-CLS, emphasizing the virtue of sawtooth ramp clamp. We explain that it is the inherent mechanosensitivity of Nav activation that underlies Nav-CLS. Using modeling of excitability, we show the known process of Nav-CLS is sufficient to predict a wide variety of "sick excitable cell" phenomena, from hyperexcitability through to depolarizing block. When living cells are mimicked by inclusion of pumps, mild Nav-CLS produces a wide array of burst phenomena and subthreshold oscillations. Dynamical analysis of mild damage scenarios shows how these phenomena reflect changes in spike thresholds as the pumps try to counteract the leaky Nav channels. Smart Nav inhibitors designed for sick excitable cells would target bleb-damaged membrane, buying time for cell-mediated removal or repair of Nav-bearing membrane that has become bleb-damaged (ie, detached from the cytoskeleton).
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Affiliation(s)
- C E Morris
- Ottawa Hospital Research Institute, Ottawa, ON, Canada
| | - B Joos
- University of Ottawa, Ottawa, ON, Canada
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Lazar A, Lenkey N, Pesti K, Fodor L, Mike A. Different pH-sensitivity patterns of 30 sodium channel inhibitors suggest chemically different pools along the access pathway. Front Pharmacol 2015; 6:210. [PMID: 26441665 PMCID: PMC4585259 DOI: 10.3389/fphar.2015.00210] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 09/08/2015] [Indexed: 11/28/2022] Open
Abstract
The major drug binding site of sodium channels is inaccessible from the extracellular side, drug molecules can only access it either from the membrane phase, or from the intracellular aqueous phase. For this reason, ligand-membrane interactions are as important determinants of inhibitor properties, as ligand-protein interactions. One-way to probe this is to modify the pH of the extracellular fluid, which alters the ratio of charged vs. uncharged forms of some compounds, thereby changing their interaction with the membrane. In this electrophysiology study we used three different pH values: 6.0, 7.3, and 8.6 to test the significance of the protonation-deprotonation equilibrium in drug access and affinity. We investigated drugs of several different indications: carbamazepine, lamotrigine, phenytoin, lidocaine, bupivacaine, mexiletine, flecainide, ranolazine, riluzole, memantine, ritanserin, tolperisone, silperisone, ambroxol, haloperidol, chlorpromazine, clozapine, fluoxetine, sertraline, paroxetine, amitriptyline, imipramine, desipramine, maprotiline, nisoxetine, mianserin, mirtazapine, venlafaxine, nefazodone, and trazodone. We recorded the pH-dependence of potency, reversibility, as well as onset/offset kinetics. As expected, we observed a strong correlation between the acidic dissociation constant (pKa) of drugs and the pH-dependence of their potency. Unexpectedly, however, the pH-dependence of reversibility or kinetics showed diverse patterns, not simple correlation. Our data are best explained by a model where drug molecules can be trapped in at least two chemically different environments: A hydrophilic trap (which may be the aqueous cavity within the inner vestibule), which favors polar and less lipophilic compounds, and a lipophilic trap (which may be the membrane phase itself, and/or lipophilic binding sites on the channel). Rescue from the hydrophilic and lipophilic traps can be promoted by alkalic and acidic extracellular pH, respectively.
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Affiliation(s)
- Alexandra Lazar
- Intensive Care Unit, University of Medicine and Pharmacy Tirgu Mures, Romania
| | - Nora Lenkey
- Lendület Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Hungarian Academy of Sciences Budapest, Hungary
| | - Krisztina Pesti
- Opto-Neuropharmacology Group, MTA-ELTE NAP B Budapest, Hungary ; János Szentágothai Doctoral School of Neurosciences, Semmelweis University Budapest, Hungary
| | - Laszlo Fodor
- Pharmacology and Drug Safety Research, Gedeon Richter Plc. Budapest, Hungary
| | - Arpad Mike
- Opto-Neuropharmacology Group, MTA-ELTE NAP B Budapest, Hungary
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Friedrich O, Reid MB, Van den Berghe G, Vanhorebeek I, Hermans G, Rich MM, Larsson L. The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill. Physiol Rev 2015; 95:1025-109. [PMID: 26133937 PMCID: PMC4491544 DOI: 10.1152/physrev.00028.2014] [Citation(s) in RCA: 228] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.
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Affiliation(s)
- O Friedrich
- Institute of Medical Biotechnology, Department of Chemical and Biological Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany; College of Health and Human Performance, University of Florida, Gainesville, Florida; Clinical Department and Laboratory of Intensive Care Medicine, Division of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium; Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio; and Department of Physiology and Pharmacology, Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, Stockholm, Sweden
| | - M B Reid
- Institute of Medical Biotechnology, Department of Chemical and Biological Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany; College of Health and Human Performance, University of Florida, Gainesville, Florida; Clinical Department and Laboratory of Intensive Care Medicine, Division of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium; Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio; and Department of Physiology and Pharmacology, Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, Stockholm, Sweden
| | - G Van den Berghe
- Institute of Medical Biotechnology, Department of Chemical and Biological Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany; College of Health and Human Performance, University of Florida, Gainesville, Florida; Clinical Department and Laboratory of Intensive Care Medicine, Division of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium; Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio; and Department of Physiology and Pharmacology, Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, Stockholm, Sweden
| | - I Vanhorebeek
- Institute of Medical Biotechnology, Department of Chemical and Biological Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany; College of Health and Human Performance, University of Florida, Gainesville, Florida; Clinical Department and Laboratory of Intensive Care Medicine, Division of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium; Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio; and Department of Physiology and Pharmacology, Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, Stockholm, Sweden
| | - G Hermans
- Institute of Medical Biotechnology, Department of Chemical and Biological Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany; College of Health and Human Performance, University of Florida, Gainesville, Florida; Clinical Department and Laboratory of Intensive Care Medicine, Division of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium; Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio; and Department of Physiology and Pharmacology, Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, Stockholm, Sweden
| | - M M Rich
- Institute of Medical Biotechnology, Department of Chemical and Biological Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany; College of Health and Human Performance, University of Florida, Gainesville, Florida; Clinical Department and Laboratory of Intensive Care Medicine, Division of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium; Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio; and Department of Physiology and Pharmacology, Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, Stockholm, Sweden
| | - L Larsson
- Institute of Medical Biotechnology, Department of Chemical and Biological Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany; College of Health and Human Performance, University of Florida, Gainesville, Florida; Clinical Department and Laboratory of Intensive Care Medicine, Division of Cellular and Molecular Medicine, KU Leuven, Leuven, Belgium; Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio; and Department of Physiology and Pharmacology, Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, Stockholm, Sweden
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Abstract
K-selective voltage-gated channels (Kv) are multi-conformation bilayer-embedded proteins whose mechanosensitive (MS) Popen(V) implies that at least one conformational transition requires the restructuring of the channel-bilayer interface. Unlike Morris and colleagues, who attributed MS-Kv responses to a cooperative V-dependent closed-closed expansion↔compaction transition near the open state, Mackinnon and colleagues invoke expansion during a V-independent closed↔open transition. With increasing membrane tension, they suggest, the closed↔open equilibrium constant, L, can increase >100-fold, thereby taking steady-state Popen from 0→1; "exquisite sensitivity to small…mechanical perturbations", they state, makes a Kv "as much a mechanosensitive…as…a voltage-dependent channel". Devised to explain successive gK(V) curves in excised patches where tension spontaneously increased until lysis, their L-based model falters in part because of an overlooked IK feature; with recovery from slow inactivation factored in, their g(V) datasets are fully explained by the earlier model (a MS V-dependent closed-closed transition, invariant L≥4). An L-based MS-Kv predicts neither known Kv time courses nor the distinctive MS responses of Kv-ILT. It predicts Kv densities (hence gating charge per V-sensor) several-fold different from established values. If opening depended on elevated tension (L-based model), standard gK(V) operation would be compromised by animal cells' membrane flaccidity. A MS V-dependent transition is, by contrast, unproblematic on all counts. Since these issues bear directly on recent findings that mechanically-modulated Kv channels subtly tune pain-related excitability in peripheral mechanoreceptor neurons we undertook excitability modeling (evoked action potentials). Kvs with MS V-dependent closed-closed transitions produce nuanced mechanically-modulated excitability whereas an L-based MS-Kv yields extreme, possibly excessive (physiologically-speaking) inhibition.
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Stimulation-induced ectopicity and propagation windows in model damaged axons. J Comput Neurosci 2014; 37:523-31. [PMID: 25110188 PMCID: PMC4224747 DOI: 10.1007/s10827-014-0521-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Revised: 07/21/2014] [Accepted: 07/23/2014] [Indexed: 12/04/2022]
Abstract
Neural tissue injuries render voltage-gated Na+ channels (Nav) leaky, thereby altering excitability, disrupting propagation and causing neuropathic pain related ectopic activity. In both recombinant systems and native excitable membranes, membrane damage causes the kinetically-coupled activation and inactivation processes of Nav channels to undergo hyperpolarizing shifts. This damage-intensity dependent change, called coupled left-shift (CLS), yields a persistent or “subthreshold” Nav window conductance. Nodes of Ranvier simulations involving various degrees of mild CLS showed that, as the system’s channel/pump fluxes attempt to re-establish ion homeostasis, the CLS elicits hyperexcitability, subthreshold oscillations and neuropathic type action potential (AP) bursts. CLS-induced intermittent propagation failure was studied in simulations of stimulated axons, but pump contributions were ignored, leaving open an important question: does mild-injury (small CLS values, pumps functioning well) render propagation-competent but still quiescent axons vulnerable to further impairments as the system attempts to cope with its normal excitatory inputs? We probe this incipient diffuse axonal injury scenario using a 10-node myelinated axon model. Fully restabilized nodes with mild damage can, we show, become ectopic signal generators (“ectopic nodes”) because incoming APs stress Na+/K+ gradients, thereby altering spike thresholds. Comparable changes could contribute to acquired sodium channelopathies as diverse as epileptic phenomena and to the neuropathic amplification of normally benign sensory inputs. Input spike patterns, we found, propagate with good fidelity through an ectopically firing site only when their frequencies exceed the ectopic frequency. This “propagation window” is a robust phenomenon, occurring despite Gaussian noise, large jitter and the presence of several consecutive ectopic nodes.
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Lachance M, Longtin A, Morris CE, Yu N, Joós B. Stimulation-induced ectopicity and propagation windows in model damaged axons. BMC Neurosci 2014. [PMCID: PMC4125029 DOI: 10.1186/1471-2202-15-s1-p134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Koesters A, Engisch KL, Rich MM. Decreased cardiac excitability secondary to reduction of sodium current may be a significant contributor to reduced contractility in a rat model of sepsis. CRITICAL CARE : THE OFFICIAL JOURNAL OF THE CRITICAL CARE FORUM 2014; 18:R54. [PMID: 24669759 PMCID: PMC4057164 DOI: 10.1186/cc13800] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Accepted: 03/03/2014] [Indexed: 01/07/2023]
Abstract
Introduction Multisystem organ failure remains a poorly understood complication of sepsis. During sepsis, reduced excitability contributes to organ failure of skeletal muscle, nerves and the spinal cord. The goal of this study was to determine whether reduced excitability might also contribute to cardiac failure during sepsis. Methods Wistar rats were made septic by cecal ligation and puncture. One day later, action potentials were recorded from beating left ventricular papillary muscle ex vivo by impaling myocytes with sharp microelectrodes. Results In cardiac papillary muscle from septic rats, action potential amplitude and rate of rise were reduced, while threshold was elevated. These changes in action potential properties suggest sepsis selectively reduces sodium current. To determine the effects of selective reduction in sodium current, we applied tetrodotoxin to papillary muscle from healthy rats and found reduction in action potential amplitude and rate of rise, as well as elevation of threshold. The changes were similar to those triggered by sepsis. Blocking calcium current using nifedipine did not mimic action potential changes induced by sepsis. Contractility of healthy papillary muscle was reduced to 40% of normal following partial block of sodium current by tetrodotoxin, close to the low contractility of septic papillary muscle, which was 30% of normal. Conclusions Our data suggest cardiac excitability is reduced during sepsis in rats. The reduction in excitability appears to be primarily due to reduction of sodium current. The reduction in sodium current may be sufficient to explain most of the reduction in cardiac contractility during sepsis.
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Force spectroscopy measurements show that cortical neurons exposed to excitotoxic agonists stiffen before showing evidence of bleb damage. PLoS One 2013; 8:e73499. [PMID: 24023686 PMCID: PMC3758302 DOI: 10.1371/journal.pone.0073499] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Accepted: 07/22/2013] [Indexed: 12/12/2022] Open
Abstract
In ischemic and traumatic brain injury, hyperactivated glutamate (N-methyl-D-aspartic acid, NMDA) and sodium (Nav) channels trigger excitotoxic neuron death. Na+, Ca++ and H2O influx into affected neurons elicits swelling (increased cell volume) and pathological blebbing (disassociation of the plasma membrane’s bilayer from its spectrin-actomyosin matrix). Though usually conflated in injured tissue, cell swelling and blebbing are distinct processes. Around an injury core, salvageable neurons could be mildly swollen without yet having suffered the bleb-type membrane damage that, by rendering channels leaky and pumps dysfunctional, exacerbates the excitotoxic positive feedback spiral. Recognizing when neuronal inflation signifies non-lethal osmotic swelling versus blebbing should further efforts to salvage injury-penumbra neurons. To assess whether the mechanical properties of osmotically-swollen versus excitotoxically-blebbing neurons might be cytomechanically distinguishable, we measured cortical neuron elasticity (gauged via atomic force microscopy (AFM)-based force spectroscopy) upon brief exposure to hypotonicity or to excitotoxic agonists (glutamate and Nav channel activators, NMDA and veratridine). Though unperturbed by solution exchange per se, elasticity increased abruptly with hypotonicity, with NMDA and with veratridine. Neurons then invariably softened towards or below the pre-treatment level, sometimes starting before the washout. The initial channel-mediated stiffening bespeaks an abrupt elevation of hydrostatic pressure linked to NMDA or Nav channel-mediated ion/H2O fluxes, together with increased [Ca++]int-mediated submembrane actomyosin contractility. The subsequent softening to below-control levels is consistent with the onset of a lethal level of bleb damage. These findings indicate that dissection/identification of molecular events during the excitotoxic transition from stiff/swollen to soft/blebbing is warranted and should be feasible.
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Desaphy JF, Chahine M. Recent advances in voltage-gated sodium channels, their pharmacology, and related diseases. Front Pharmacol 2013; 4:52. [PMID: 23616770 PMCID: PMC3629309 DOI: 10.3389/fphar.2013.00052] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Accepted: 04/04/2013] [Indexed: 12/02/2022] Open
Affiliation(s)
- Jean-François Desaphy
- Section of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari - Aldo Moro Bari, Italy
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Yu N, Morris CE, Joós B, Longtin A. Spontaneous excitation patterns computed for axons with injury-like impairments of sodium channels and Na/K pumps. PLoS Comput Biol 2012; 8:e1002664. [PMID: 23028273 PMCID: PMC3441427 DOI: 10.1371/journal.pcbi.1002664] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 07/13/2012] [Indexed: 11/28/2022] Open
Abstract
In injured neurons, “leaky” voltage-gated sodium channels (Nav) underlie dysfunctional excitability that ranges from spontaneous subthreshold oscillations (STO), to ectopic (sometimes paroxysmal) excitation, to depolarizing block. In recombinant systems, mechanical injury to Nav1.6-rich membranes causes cytoplasmic Na+-loading and “Nav-CLS”, i.e., coupled left-(hyperpolarizing)-shift of Nav activation and availability. Metabolic injury of hippocampal neurons (epileptic discharge) results in comparable impairment: left-shifted activation and availability and hence left-shifted INa-window. A recent computation study revealed that CLS-based INa-window left-shift dissipates ion gradients and impairs excitability. Here, via dynamical analyses, we focus on sustained excitability patterns in mildly damaged nodes, in particular with more realistic Gaussian-distributed Nav-CLS to mimic “smeared” injury intensity. Since our interest is axons that might survive injury, pumps (sine qua non for live axons) are included. In some simulations, pump efficacy and system volumes are varied. Impacts of current noise inputs are also characterized. The diverse modes of spontaneous rhythmic activity evident in these scenarios are studied using bifurcation analysis. For “mild CLS injury”, a prominent feature is slow pump/leak-mediated EIon oscillations. These slow oscillations yield dynamic firing thresholds that underlie complex voltage STO and bursting behaviors. Thus, Nav-CLS, a biophysically justified mode of injury, in parallel with functioning pumps, robustly engenders an emergent slow process that triggers a plethora of pathological excitability patterns. This minimalist “device” could have physiological analogs. At first nodes of Ranvier and at nociceptors, e.g., localized lipid-tuning that modulated Nav midpoints could produce Nav-CLS, as could co-expression of appropriately differing Nav isoforms. Nerve cells damaged by trauma, stroke, epilepsy, inflammatory conditions etc, have chronically leaky sodium channels that eventually kill. The usual job of sodium channels is to make brief voltage signals –action potentials– for long distance propagation. After sodium channels open to generate action potentials, sodium pumps work harder to re-establish the intracellular/extracellular sodium imbalance that is, literally, the neuron's battery for firing action potentials. Wherever tissue damage renders membranes overly fluid, we hypothesize, sodium channels become chronically leaky. Our experimental findings justify this. In fluidized membranes, sodium channel voltage sensors respond too easily, letting channels spend too much time open. Channels leak, pumps respond. By mathematical modeling, we show that in damaged channel-rich membranes the continual pump/leak counterplay would trigger the kinds of bizarre intermittent action potential bursts typical of injured neurons. Arising ectopically from injury regions, such neuropathic firing is unrelated to events in the external world. Drugs that can silence these deleterious electrical barrages without blocking healthy action potentials are needed. If fluidized membranes house the problematic leaky sodium channels, then drug side effects could be diminished by using drugs that accumulate most avidly into fluidized membranes, and that bind their targets with highest affinity there.
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Affiliation(s)
- Na Yu
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
| | | | - Béla Joós
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
- * E-mail:
| | - André Longtin
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
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Morris CE, Juranka PF, Joós B. Perturbed voltage-gated channel activity in perturbed bilayers: implications for ectopic arrhythmias arising from damaged membrane. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2012; 110:245-56. [PMID: 22846437 DOI: 10.1016/j.pbiomolbio.2012.07.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 07/11/2012] [Indexed: 12/31/2022]
Abstract
The ceaseless opening and closing of the voltage-gated channels (VGCs) underlying cardiac rhythmicity is controlled, in each VGC, by four mobile voltage sensors embedded in bilayer. Every action potential necessitates extensive packing/repacking of voltage sensor domains with adjacent interacting lipid molecules. This renders VGC activity mechanosensitive (MS), i.e., energetically sensitive to the bilayer's mechanical state. Irreversible perturbations of sarcolemmal bilayer such as those associated with ischemia, reperfusion, inflammation, cortical-cytoskeleton abnormalities, bilayer-disrupting toxins, diet aberrations, etc, should therefore perturb VGC activity. Disordered/fluidized bilayer states that facilitate voltage sensor repacking, and thus make VGC opening too easy could, therefore, explain VGC-leakiness in these conditions. To study this in membrane patches we impose mechanical blebbing injury during pipette aspiration-induced membrane stretch, a process that modulates VGC activity irreversibly (plastic regime) and then, eventually, reversibly (elastic regime). Because of differences in sensor-to-gate coupling among different VGCs, their responses to stretch fall into two major categories, MS-Speed, MS-Number, exemplified by Nav and Cav channels. For particular VGCs in perturbed bilayers, leak mechanisms depend on whether or not the rate-limiting voltage-dependent step is MS. Mode-switch transitions might also be mechanosensitive and thus play a role. Incorporated mathematically in axon models, plastic-regime Nav responses elicit ectopic firing behaviors typical of peripheral neuropathies. In cardiomyocytes with mild bleb damage, Nav and/or Cav leaks from irreversible MS modulation (MS-Speed, MS-Number, respectively) could, similarly, foster ectopic arrhythmias. Where pathologically leaky VGCs reside in damaged bilayer, peri-channel bilayer disorder/fluidity conditions could be an important "target feature" for anti-arrhythmic VGC drugs.
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Boucher PA, Joós B, Morris CE. Coupled left-shift of Nav channels: modeling the Na⁺-loading and dysfunctional excitability of damaged axons. J Comput Neurosci 2012; 33:301-19. [PMID: 22476614 DOI: 10.1007/s10827-012-0387-7] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2011] [Revised: 01/25/2012] [Accepted: 02/12/2012] [Indexed: 11/29/2022]
Abstract
Injury to neural tissue renders voltage-gated Na⁺ (Nav) channels leaky. Even mild axonal trauma initiates Na⁺-loading, leading to secondary Ca²⁺-loading and white matter degeneration. The nodal isoform is Nav1.6 and for Nav1.6-expressing HEK-cells, traumatic whole cell stretch causes an immediate tetrodotoxin-sensitive Na⁺-leak. In stretch-damaged oocyte patches, Nav1.6 current undergoes damage-intensity dependent hyperpolarizing- (left-) shifts, but whether left-shift underlies injured-axon Nav-leak is uncertain. Nav1.6 inactivation (availability) is kinetically limited by (coupled to) Nav activation, yielding coupled left-shift (CLS) of the two processes: CLS should move the steady-state Nav1.6 "window conductance" closer to typical firing thresholds. Here we simulated excitability and ion homeostasis in free-running nodes of Ranvier to assess if hallmark injured-axon behaviors--Na⁺-loading, ectopic excitation, propagation block--would occur with Nav-CLS. Intact/traumatized axolemma ratios were varied, and for some simulations Na/K pumps were included, with varied in/outside volumes. We simulated saltatory propagation with one mid-axon node variously traumatized. While dissipating the [Na⁺] gradient and hyperactivating the Na/K pump, Nav-CLS generated neuropathic pain-like ectopic bursts. Depending on CLS magnitude, fraction of Nav channels affected, and pump intensity, tonic or burst firing or nodal inexcitability occurred, with [Na⁺] and [K⁺] fluctuating. Severe CLS-induced inexcitability did not preclude Na⁺-loading; in fact, the steady-state Na⁺-leaks elicited large pump currents. At a mid-axon node, mild CLS perturbed normal anterograde propagation, and severe CLS blocked saltatory propagation. These results suggest that in damaged excitable cells, Nav-CLS could initiate cellular deterioration with attendant hyper- or hypo-excitability. Healthy-cell versions of Nav-CLS, however, could contribute to physiological rhythmic firing.
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