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Rodrigues AM, Silva DB, Miranda MF, Braga da Silva SC, Canton Santos LE, Scorza FA, Scorza CA, Moret MA, Guimarães de Almeida AC. The Effect of Low Magnesium Concentration on Ictal Discharges In A Non-Synaptic Model. Int J Neural Syst 2020; 31:2050070. [PMID: 33357154 DOI: 10.1142/s0129065720500707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Magnesium (Mg[Formula: see text] is an essential mineral for several cellular functions. The concentration of this ion below the physiological concentration induces recurrent neuronal discharges both in slices of the hippocampus and in neuronal cultures. These epileptiform discharges are initially sensitive to the application of [Formula: see text]-methyl-D-aspartate (NMDA) receptor antagonists, but these antagonists may lose their effectiveness with prolonged exposure to low [Mg[Formula: see text]], when extracellular Ca[Formula: see text] reduction occurs, typical of ictal periods, indicating the absence of synaptic connections. The study herein presented aimed at investigating the effect of reducing the [Mg[Formula: see text]] during the induction of Nonsynaptic Epileptiform Activities (NSEA). As an experimental protocol, NSEA were induced in rat hippocampal dentate gyrus (DG), using a bath solution containing high-K[Formula: see text] and zero-added-Ca[Formula: see text]. Additionally, computer simulations were performed using a mathematical model that represents electrochemical characteristics of the tissue of the DG granular layer. The experimental results show that the reduction of [Mg[Formula: see text]] causes an increase in the duration of the ictal period and a reduction in the interictal period, intensifying epileptiform discharges. The computer simulations suggest that the reduction of the Mg[Formula: see text] level intensifies the epileptiform discharges by a joint effect of reducing the surface charge screening and reducing the activity of the Na/K pump.
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Affiliation(s)
- Antônio Márcio Rodrigues
- Laboratório de Neurociência, Experimental e Computacional, Departamento de Engenharia de, Biossistemas Universidade Federal de São João del-Rei, Pr. Dom Helvécio, 74, 36.301-160 São João del-Rei, MG, Brazil
| | - Delmo Benedito Silva
- Laboratório de Neurociência, Experimental e Computacional, Departamento de Engenharia de, Biossistemas Universidade Federal de São João del-Rei, Pr. Dom Helvécio, 74, 36.301-160 São João del-Rei, MG, Brazil
| | - Maísa Ferreira Miranda
- Laboratório de Neurociência, Experimental e Computacional, Departamento de Engenharia de, Biossistemas Universidade Federal de São João del-Rei, Pr. Dom Helvécio, 74, 36.301-160 São João del-Rei, MG, Brazil
| | - Silvia Cristina Braga da Silva
- Laboratório de Neurociência, Experimental e Computacional, Departamento de Engenharia de, Biossistemas Universidade Federal de São João del-Rei, Pr. Dom Helvécio, 74, 36.301-160 São João del-Rei, MG, Brazil
| | - Luiz Eduardo Canton Santos
- Laboratório de Neurociência, Experimental e Computacional, Departamento de Engenharia de, Biossistemas Universidade Federal de São João del-Rei, Pr. Dom Helvécio, 74, 36.301-160 São João del-Rei, MG, Brazil
| | - Fulvio Alexandre Scorza
- Disciplina de Neurociência, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Carla Alessandra Scorza
- Disciplina de Neurociência, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Marcelo A Moret
- UNEB - Rua Silveira Martins, 2555, Cabula 41150-000 Salvador, Bahia, Brazil
| | - Antônio-Carlos Guimarães de Almeida
- Laboratório de Neurociência, Experimental e Computacional, Departamento de Engenharia de, Biossistemas Universidade Federal de São João del-Rei, Pr. Dom Helvécio, 74, 36.301-160 São João del-Rei, MG, Brazil
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Abstract
The endogenous polyamines spermine, spermidine and putrescine are present at high concentrations inside neurons and can be released into the extracellular space where they have been shown to modulate ion channels. Here, we have examined polyamine modulation of voltage-activated Ca(2+) channels (VACCs) and voltage-activated Na(+) channels (VANCs) in rat superior cervical ganglion neurons using whole-cell voltage-clamp at physiological divalent concentrations. Polyamines inhibited VACCs in a concentration-dependent manner with IC(50)s for spermine, spermidine, and putrescine of 4.7 +/- 0.7, 11.2 +/- 1.4 and 90 +/- 36 mM, respectively. Polyamines caused inhibition by shifting the VACC half-activation voltage (V(0.5)) to depolarized potentials and by reducing total VACC permeability. The shift was described by Gouy-Chapman-Stern theory with a surface charge density of 0.120 +/- 0.005 e(-) nm(-2) and a surface potential of -19 mV. Attenuation of spermidine and spermine inhibition of VACC at decreased pH was explained by H(+) titration of surface charge. Polyamine-mediated effects also decreased at elevated pH due to the inhibitors having lower valence and being less effective at screening surface charge. Polyamines affected VANC currents indirectly by reducing TTX inhibition of VANCs at high pH. This may reflect surface charge induced decreases in the local TTX concentration or polyamine-TTX interactions. In conclusion, polyamines inhibit neuronal VACCs via complex interactions with extracellular H(+) and Ca. Many of the observed effects can be explained by a model incorporating polyamine binding, H(+) binding and surface charge screening.
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Affiliation(s)
- Wenyan Chen
- Division of Pulmonary and Critical Care Medicine; Oregon Health and Science University; Portland, Oregon USA
| | - Mark T. Harnett
- Division of Pulmonary and Critical Care Medicine; Oregon Health and Science University; Portland, Oregon USA
| | - Stephen M. Smith
- Division of Pulmonary and Critical Care Medicine; Oregon Health and Science University; Portland, Oregon USA
- Department of Physiology and Pharmacology; Oregon Health and Science University; Portland, Oregon USA
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