Extracellular Conductance Research Articles

Stress System Activation Analysis in Greek Female Adolescents: A Bioimpedance Study.

Adolescence is a developmental stage characterized by endocrine-induced physical and psychosocial changes in stress responsiveness. The stress-sensitive cortical and limbic brain regions, which continue to develop during adolescence and young adulthood, may be vulnerable to such changes, yet have not yet been extensively investigated. To examine the activation state of the stress system in adolescence and to show its physiologic relevance, we employed Electrolytic Extracellular Tomography measurement cycles by bioimpedance (TomEEx, BioTekna Co, Venice). Analysis of changes in Basal Extracellular Conductance (BEC) and systemic hydroelectrolytic distribution (DECW + and DECW-) markers were obtained. The statistical analysis was performed using nonparametric tests. The highest possible precision (in statistics) was detected by a meta-analytic tool: Hedge's g correction for small samples bias. Stress system activity, BMI, and BEC, a biomarker of systemic inflammation, were significantly different in adolescents classified according to their depressive symptoms or self-preoccupation (p<0.05). Importantly, BEC measures were predicted by stress activation system (p<0.05). The results contribute to the understanding of the mediating processes in different stress activation-related states and inflammation during adolescence.

Chronic Systemic Inflammation Measured by Bioimpedance Technology Before and After Sleeve Gastrectomy: A Feasibility Study.

Stress induces obesity, while extreme obesity causes stress, anxiety, and even depression. Yet, knowledge on the underlying mechanism(s) has many gaps. To this end, we designed a feasibility study, focused on 18 bariatric patients recruited by the First Propaideutic Department of Surgery at the Hippokration University Hospital in Athens, Greece. The patients (aged 23-58 y, weight 101-185.4 kg before surgery) were weighted and evaluated by advanced bioimpedance technology 2-3days before surgery at the Biomedical Research Foundation of the Academy of Athens. We employed Bioimpedance Electrolytic Extracellular Tomography (Tomeex), which characterizes (a) neurodegenerative responsiveness to stress, (b) sensory and autonomic tones by basal extracellular conductance (BEC), and (c) activity of limbic and cortical brain areas. The patients' mean body weight loss after 6months was 48.8±3.1Kg, while stress levels evaluated by appropriate questionnaires decreased (Spearman coefficient significance level p<0.05). Anxiety and depressive symptoms decreased by 70%, accompanied by changes in measured sensory and autonomic tones (p=0.003). Baseline blood markers, such as hsCRP and glucose, predicted lower abdominal inflammation (p=0.034 and p=0.058, respectively) 6months postoperatively. In conclusion, chronic inflammation measures by bioimpedance are a useful non-invasive monitoring tool in bariatric surgery.

Mechano-stimulation initiated by extracellular adhesion and cationic conductance pathways influence astrocyte activation

Traumatic brain injury (TBI) represents a major cause of long-term disability worldwide. Primary damage to brain tissue leads to complex secondary injury mechanisms involving inflammation, oxidative stress and cellular activation/reactivity. The molecular pathways that exacerbate brain cell dysfunction after injury are not well understood and provide challenges to developing TBI therapeutics. This study aimed to delineate mechanisms of astrocyte activation induced by mechano-stimulation, specifically involving extracellular adhesion and cationic transduction. An in vitro model was employed to investigate 2D and 3D cultures of primary astrocytes, in which cells were exposed to a single high-rate overpressure known to cause upregulation of structural and proliferative markers within 72 h of exposure. An inhibitor of focal adhesion kinase (FAK) phosphorylation, TAE226, was used to demonstrate a relationship between extracellular adhesion perturbations and structural reactivity in the novel 3D model. TAE226 mitigated upregulation of glial fibrillary acidic protein in 3D cultures by 72 h post-exposure. Alternatively, incubation with gadolinium (a cationic channel blocker) during overpressure, demonstrated a role for cationic transduction in reducing the increased levels of proliferating cell nuclear antigen that occur at 24 h post-stimulation. Furthermore, early changes in mitochondrial polarization at 15 min and in endogenous ATP levels at 4−6 h occur post-overpressure and may be linked to later changes in cell phenotype. By 24 h, there was evidence of increased amine metabolism and increased nicotinamide adenine dinucleotide phosphate oxidase (NOX4) production. The overproduction of NOX4 was counteracted by gadolinium during overpressure exposure. Altogether, the results of this study indicated that both extracellular adhesion (via FAK activation) and cationic conductance (via ion channels) contribute to early patterns of astrocyte activation following overpressure stimulation. Mechano-stimulation pathways are linked to bioenergetic and metabolic disruptions in astrocytes that influence downstream oxidative stress, aberrant proliferative capacity and structural reactivity.

Diverse small molecules prevent macrophage lysis during pyroptosis

Pyroptosis is a programmed process of proinflammatory cell death mediated by caspase-1-related proteases that cleave the pore-forming protein, gasdermin D, causing cell lysis and release of inflammatory intracellular contents. The amino acid glycine prevents pyroptotic lysis via unknown mechanisms, without affecting caspase-1 activation or pore formation. Pyroptosis plays a critical role in diverse inflammatory diseases, including sepsis. Septic lethality is prevented by glycine treatment, suggesting that glycine-mediated cytoprotection may provide therapeutic benefit. In this study, we systematically examined a panel of small molecules, structurally related to glycine, for their ability to prevent pyroptotic lysis. We found a requirement for the carboxyl group, and limited tolerance for larger amino groups and substitution of the hydrogen R group. Glycine is an agonist for the neuronal glycine receptor, which acts as a ligand-gated chloride channel. The array of cytoprotective small molecules we identified resembles that of known glycine receptor modulators. However, using genetically deficient Glrb mutant macrophages, we found that the glycine receptor is not required for pyroptotic cytoprotection. Furthermore, protection against pyroptotic lysis is independent of extracellular chloride conductance, arguing against an effect mediated by ligand-gated chloride channels. Finally, we conducted a small-scale, hypothesis-driven small-molecule screen and identified unexpected ion channel modulators that prevent pyroptotic lysis with increased potency compared to glycine. Together, these findings demonstrate that pyroptotic lysis can be pharmacologically modulated and pave the way toward identification of therapeutic strategies for pathologic conditions associated with pyroptosis.

Effects of precompression time and strength on the physical characteristics of quasi-stapled porcine small intestinal tissue.

Precompression is vital when performing gastrointestinal anastomosis with staplers. However, research on the internal changes in intestinal tissue under stapling is lacking, and the effects of precompression have not been clarified. In this study, a stapler was modified, and the multifrequency bioimpedance of porcine small intestinal tissue was measured from before clamping the tissue with the stapler until the release of the tissue after precompression without firing. The Cole Y model was fitted to the bioimpedance, and the changes in the tissue were analyzed using the model parameters: G0, extracellular fluid conductance, and Δ G, intracellular fluid conductance. The results show that the changes of G0 and Δ G could be divided into four stages: rapid decrease, slow decrease, intense resilience, and slow recovery. During slow decrease stage, there was a greater decrease of G0 and Δ G (1.02E-05 ± 1.12E-05 S and 1.73E-05 ± 2.12E-05 S in precompression time's increase, 1.68E-05 ± 8.74E-06 S and 1.20E-05 ± 1.09E-05 S in precompression strength's increase). On the contrary, during intense resilience stage, there was a less increase of G0 and Δ G (0.88E-05 ± 4.86E-05 S and 9.15E-05 ± 9.37E-05 S in precompression time's increase, 2.72E-05 ± 3.53E-05 S and 1.02E-04 ± 8.54E-05 S in precompression strength's increase). In conclusion, the effects of precompression factors on tissue have been preliminary revealed: the tissue under precompression becomes thinner and less resilient. To improve the precompression effects and reduce any excessive pressure exerted on the staples by tissue resilience, the precompression time and strength should be increased appropriately.

Changes in Small Intestine Tissue Compressed by a Linear Stapler Based on Cole Y Model.

Clarifying changes in gastrointestinal tissue compressed by surgical stapler is a crucial prerequisite for stapler design optimization. For this study, a stapler was modified, and multifrequency bioimpedance of a porcine small intestine tissue compressed by the stapler was measured. The Cole Y model was fitted to the bioimpedance, and changes in tissue were analyzed using model parameters: G 0, extracellular fluid conductance; ΔG, intracellular fluid conductance; C cpeF, equivalent capacitance of cell membrane. The changes could be divided into two stages: first, all parameters decreased sharply with slopes more than 15.70±2.67, 4.25±1.23μS/s and 72.68±6.99pF/s respectively; and subsequently, with an increase in compression strength, G 0 decreased with slopes less than 2.54±0.40μS/s, ΔG decreased slightly with slope of 0.26±0.04μS/s after fluctuating mildly, and C cpeF remained nearly invariant after initially increasing with slope of -2.94±0.64pF/s. In conclusion, when the stapler is closed, a portion of tissue is squeezed out of the measurement space, causing all parameters' sharp decrease. Subsequently, the stapler continues compressing the tissue, leading to extracellular fluid expulsion. The changes in intracellular fluid are related to the compression strength and may be explained by cell restoration. This study could provide a basis for stapler design optimization.

The Multi-Domain Fibroblast/Myocyte Coupling in the Cardiac Tissue: A Theoretical Study.

Cardiac fibroblast proliferation and concomitant collagenous matrix accumulation (fibrosis) develop during multiple cardiac pathologies. Recent studies have demonstrated direct electrical coupling between myocytes and fibroblasts in vitro, and assessed the electrophysiological implications of such coupling. However, in the living tissues, such coupling has not been demonstrated, and only indirect coupling via the extracellular space is likely to exist. In this study we employed a multi-domain model to assess the modulation of the cardiac electrophysiological properties by neighboring fibroblasts assuming only indirect coupling. Numerical simulations in 1D and 2D human atrial models showed that extracellular coupling sustains a significant impact on conduction velocity (CV) and a less significant effect on the action potential duration. Both CV and the slope of the CV restitution increased with increasing fibroblast density. This effect was more substantial for lower extracellular conductance. In 2D, spiral waves exhibited reduced frequency with increasing fibroblast density, and the propensity of wavebreaks and complex dynamics at high pacing rates significantly increased.

Modelling in vivo action potential propagation along a giant axon

A partial differential equation model for the three-dimensional current flow in an excitable, unmyelinated axon is considered. Where the axon radius is significantly below a critical value R(crit) (that depends upon intra- and extra-cellular conductivity and ion channel conductance) the resistance of the intracellular space is significantly higher than that of the extracellular space, such that the potential outside the axon is uniformly small whilst the intracellular potential is approximated by the transmembrane potential. In turn, since the current flow is predominantly axial, it can be shown that the transmembrane potential is approximated by a solution to the one-dimensional cable equation. It is noted that the radius of the squid giant axon, investigated by (Hodgkin and Huxley 1952e), lies close to R(crit). This motivates us to apply the three-dimensional model to the squid giant axon and compare the results thus found to those obtained using the cable equation. In the context of the in vitro experiments conducted in (Hodgkin and Huxley 1952e) we find only a small difference between the wave profiles determined using these two different approaches and little difference between the speeds of action potential propagation predicted. This suggests that the cable equation approximation is accurate in this scenario. However when applied to the it in vivo setting, in which the conductivity of the surrounding tissue is considerably lower than that of the axoplasm, there are marked differences in both wave profile and speed of action potential propagation calculated using the two approaches. In particular, the cable equation significantly over predicts the increase in the velocity of propagation as axon radius increases. The consequences of these results are discussed in terms of the evolutionary costs associated with increasing the speed of action potential propagation by increasing axon radius.

Structural and functional analysis of critical amino acids in TMVI of the NHE1 isoform of the Na+/H+ exchanger

The mammalian Na+/H+ exchanger isoform 1 (NHE1) resides on the plasma membrane and exchanges one intracellular H+ for one extracellular Na+. It maintains intracellular pH and regulates cell volume, and cell functions including growth and cell differentiation. Previous structural and functional studies on TMVI revealed several amino acids that are potentially pore lining. We examined these and other critical residues by site-directed mutagenesis substituting Asn227→Ala, Asp, Arg; Ile233→Ala; Leu243→Ala; Glu247→Asp, Gln; Glu248→Asp, Gln. Mutant NHE1 proteins were characterized in AP-1 cells, which do not express endogenous NHE1. All the TMVI critical amino acids were highly sensitive to substitution and changes often lead to a dysfunctional protein. Mutations of Asn227→Ala, Asp, Arg; Ile233→Ala; Leu243→Ala; Glu247→Asp; Glu248→Gln yielded significant reduction in NHE1 activity. Mutants of Asn227 demonstrated defects in protein expression, targeting and activity. Substituting Asn227→Arg and Ile233→Ala decreased the surface localization and expression of NHE1 respectively. The pore lining amino acids Ile233 and Leu243 were both essential for activity. Glu247 was not essential, but the size of the residue at this location was important while the charge on residue Glu248 was more critical to NHE1 function. Limited trypsin digestion on Leu243→Ala and Glu248→Gln revealed that they had increased susceptibility to proteolytic attack, indicating an alteration in protein conformation. Modeling of TMVI with TMXI suggests that these TM segments form part of the critical fold of NHE1 with Ile233 and Leu465 of TMXI forming a critical part of the extracellular facing ion conductance pathway.

Modulation of the Extracellular Divalent Cation-inhibited Non-selective Conductance in Cardiac Cells by Metabolic Inhibition and by Oxidants

The effect of metabolic inhibition and oxidative stress on the monovalent cation-permeable, extracellular divalent cation-inhibited non-selective conductance was investigated in ventricular myocytes at 22°C. Under whole-cell voltage-clamp, with L-type Ca2+channels blocked by nifedipine, and K+currents blocked by Cs+substitution for K+, removal of Ca2+oand Mg2+oinduced a non-selective current (INS-(Ca)o) in mouse, rabbit and rat cells. Removal of glucose increased INS-(Ca)oin the absence of Ca2+oand Mg2+o, but failed to induce this current in the presence of the divalent cations. Further inhibition of glycolysis by 2-deoxyglucose (DOG; 10 m m, in zero glucose) or of mitochondrial function by rotenone (10 μ m) or NaCN (5 m m) also failed to induce INS-(Ca)oin the presence of Ca2+oand Mg2+o. Even when given together, DOG and rotenone did not induce INS-(Ca)oin the presence of divalent cations. Preactivated INS-(Ca)owas increased by the oxidants thimerosal (50 μ m), diamide (500 μ m) and pCMPS (50μ m). However, none of these drugs nor NEM (1 m m) did elicit INS-(Ca)oin the presence of Ca2+oand Mg2+o. Exposure of rat myocytes to Ag+induced a current resembling INS-(Ca)o(reversing at −5 mV; blocked by 100 μ m Gd3+) even in the presence of divalent cations. The data indicate that metabolic inhibition only regulates activated INS-(Ca)obut does not induce the opening of closed channels, and that small oxidants like Ag+may induce INS-(Ca)oactivation by accessing at sites unavailable for larger molecules.

Glutathione Deficiency Accentuates Hepatocellular Fluid Accumulation after Ischemia-Reperfusion

Liver ischemia-reperfusion is known to be associated with free radical-mediated hepatocellular damage but alterations in hepatocellular fluid flux under these conditions are incompletely understood. Deficiency of the antioxidant glutathione, which increases the liver's susceptibility to ischemia-reperfusion injury, may exacerbate pathological fluid shifts. This study examined alterations in hepatic fluid dynamics during liver ischemia-reperfusion in glutathione-deficient and glutathione-replete rats. Normal and glutathione-deficient rats underwent liver ischemia-reperfusion. Changes in hepatic extra- and intracellular fluid were monitored by calculating extra- and intracellular conductance from liver multifrequency bioelectrical impedance measurements. Liver malonyl dialdehyde content and plasma transaminase concentrations were measured and correlated with changes in hepatic impedance. Hepatic extracellular conductance decreased during ischemia and returned toward baseline values during reperfusion in a similar fashion in both study groups. Intracellular conductance increased during ischemia in both groups and continued to rise during the initial phase of reperfusion before falling toward normal. Glutathione-deficient rats had a significantly higher intracellular conductance during early reperfusion compared to controls. Glutathione-depleted rats also had higher serum transaminases and liver malonyl dialdehyde content following reperfusion. Intracellular and extracellular conductance were significantly correlated with hepatic malonyl dialdehyde content. We conclude that (1) liver ischemia-reperfusion results in movement of fluid from the extracellular to intracellular space with hepatocellular swelling; (2) glutathione deficiency accentuates hepatocyte swelling following ischemia-reperfusion; and (3) changes in extraand intracellular fluid are related to the severity of membrane damage. Multifrequency impedance analysis can be used to monitor real-time changes in hepatocyte injury and to study the effect of potential therapeutic interventions.

Electrical Properties and Ion Permeabilities in Intestinal Epithelia

The ionic permeabilities and conductive properties across intestinal epithelia were reviewed from the electrophysiological point of view. Based on our own data on the electrical parameters required for application of the equivalent circuit analysis, the contribution of an extracellular shunt conductance and that of an electrogenic sodium pump to the electrical properties of small intestine were estimated. In order to throw light upon the origin of a solute evoked potential changes, the changes in electrical parameters induced by an active solute transport were discussed.