scholarly journals Modulating cardiac conduction during metabolic ischemia with perfusate sodium and calcium in guinea pig hearts

2019 ◽  
Vol 316 (4) ◽  
pp. H849-H861 ◽  
Author(s):  
Sharon A. George ◽  
Gregory Hoeker ◽  
Patrick J. Calhoun ◽  
Michael Entz ◽  
Tristan B. Raisch ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Gap Junction ◽  
Cardiac Electrophysiology ◽  
Expression Patterns ◽  
Immunoblot Analysis ◽  
Cardiac Conduction ◽  
Cx43 Expression ◽  
Transmission Electron ◽  
Cx 43 ◽  
Extracellular Sodium

We previously demonstrated that altering extracellular sodium (Nao) and calcium (Cao) can modulate a form of electrical communication between cardiomyocytes termed “ephaptic coupling” (EpC), especially during loss of gap junction coupling. We hypothesized that altering Nao and Cao modulates conduction velocity (CV) and arrhythmic burden during ischemia. Electrophysiology was quantified by optically mapping Langendorff-perfused guinea pig ventricles with modified Nao (147 or 155 mM) and Cao (1.25 or 2.0 mM) during 30 min of simulated metabolic ischemia (pH 6.5, anoxia, aglycemia). Gap junction-adjacent perinexal width ( WP), a candidate cardiac ephapse, and connexin (Cx)43 protein expression and Cx43 phosphorylation at S368 were quantified by transmission electron microscopy and Western immunoblot analysis, respectively. Metabolic ischemia slowed CV in hearts perfused with 147 mM Nao and 2.0 mM Cao; however, theoretically increasing EpC with 155 mM Nao was arrhythmogenic, and CV could not be measured. Reducing Cao to 1.25 mM expanded WP, as expected during ischemia, consistent with reduced EpC, but attenuated CV slowing while delaying arrhythmia onset. These results were further supported by osmotically reducing WP with albumin, which exacerbated CV slowing and increased early arrhythmias during ischemia, whereas mannitol expanded WP, permitted conduction, and delayed the onset of arrhythmias. Cx43 expression patterns during the various interventions insufficiently correlated with observed CV changes and arrhythmic burden. In conclusion, decreasing perfusate calcium during metabolic ischemia enhances perinexal expansion, attenuates conduction slowing, and delays arrhythmias. Thus, perinexal expansion may be cardioprotective during metabolic ischemia. NEW & NOTEWORTHY This study demonstrates, for the first time, that modulating perfusate ion composition can alter cardiac electrophysiology during simulated metabolic ischemia.

scholarly journals Extracellular sodium dependence of the conduction velocity-calcium relationship: evidence of ephaptic self-attenuation

2016 ◽  
Vol 310 (9) ◽  
pp. H1129-H1139 ◽  
Author(s):  
Sharon A. George ◽  
Mohammad Bonakdar ◽  
Michael Zeitz ◽  
Rafael V. Davalos ◽  
James W. Smyth ◽  
...  
Keyword(s):  
Conduction Velocity ◽  
Ionic Currents ◽  
Electrical Impedance Spectroscopy ◽  
Cardiac Conduction ◽  
Cx43 Expression ◽  
Transmission Electron ◽  
Theoretical Predictions ◽  
Gap Junctional ◽  
Extracellular Sodium ◽  
Junctional Resistance

Our laboratory previously demonstrated that perfusate sodium and potassium concentrations can modulate cardiac conduction velocity (CV) consistent with theoretical predictions of ephaptic coupling (EpC). EpC depends on the ionic currents and intercellular separation in sodium channel rich intercalated disk microdomains like the perinexus. We suggested that perinexal width (WP) correlates with changes in extracellular calcium ([Ca2+]o). Here, we test the hypothesis that increasing [Ca2+]o reduces WP and increases CV. Mathematical models of EpC also predict that reducing WP can reduce sodium driving force and CV by self-attenuation. Therefore, we further hypothesized that reducing WP and extracellular sodium ([Na+]o) will reduce CV consistent with ephaptic self-attenuation. Transmission electron microscopy revealed that increasing [Ca2+]o (1 to 3.4 mM) significantly decreased WP. Optically mapping wild-type (WT) (100% Cx43) mouse hearts demonstrated that increasing [Ca2+]o increases transverse CV during normonatremia (147.3 mM), but slows transverse CV during hyponatremia (120 mM). Additionally, CV in heterozygous (∼50% Cx43) hearts was more sensitive to changes in [Ca2+]o relative to WT during normonatremia. During hyponatremia, CV slowed in both WT and heterozygous hearts to the same extent. Importantly, neither [Ca2+]o nor [Na+]o altered Cx43 expression or phosphorylation determined by Western blotting, or gap junctional resistance determined by electrical impedance spectroscopy. Narrowing WP, by increasing [Ca2+]o, increases CV consistent with enhanced EpC between myocytes. Interestingly, during hyponatremia, reducing WP slowed CV, consistent with theoretical predictions of ephaptic self-attenuation. This study suggests that serum ion concentrations may be an important determinant of cardiac disease expression.

scholarly journals Interstitial volume modulates the conduction velocity-gap junction relationship

2012 ◽  
Vol 302 (1) ◽  
pp. H278-H286 ◽  
Author(s):  
Rengasayee Veeraraghavan ◽  
Mohamed E. Salama ◽  
Steven Poelzing
Keyword(s):  
Guinea Pig ◽  
Gap Junction ◽  
Conduction Velocity ◽  
Important Determinant ◽  
Cardiac Conduction ◽  
Cell Width ◽  
Interstitial Volume ◽  
Ventricular Tachycardias ◽  
The Relationship ◽  
Isolated Cell

Cardiac conduction through gap junctions is an important determinant of arrhythmia susceptibility. Yet, the relationship between degrees of Gj uncoupling and conduction velocity (θ) remains controversial. Conflicting results in similar experiments are normally attributed to experimental differences. We hypothesized that interstitial volume modulates conduction velocity and its dependence on Gj. Interstitial volume (VIS) was quantified histologically from guinea pig right ventricle. Optical mapping was used to quantify conduction velocity and anisotropy (ARθ). Albumin (4 g/l) decreased histologically assessed VIS, increased transverse θ by 71 ± 10%, and lowered ARθ. Furthermore, albumin did not change isolated cell size. Conversely, mannitol increased VIS, decreased transverse θ by 24 ± 4%, and increased ARθ. Mannitol also decreased cell width by 12%. Furthermore, mannitol was associated with spontaneous ventricular tachycardias in three of eight animals relative to zero of 15 during control. The θ-Gj relationship was assessed using the Gj uncoupler carbenoxolone (CBX). Whereas 13 μM CBX did not significantly affect θ during control, it slowed transverse θ by 38 ± 9% during mannitol (edema). These data suggest changes in VIS modulate θ, ARθ, and the θ-Gj relationship and thereby alter arrhythmia susceptibility. Therefore, VIS may underlie arrhythmia susceptibility, particularly in diseases associated with gap junction remodeling.

scholarly journals Gap junction heterogeneity as mechanism for electrophysiologically distinct properties across the ventricular wall

2010 ◽  
Vol 298 (3) ◽  
pp. H787-H794 ◽  
Author(s):  
Maria Strom ◽  
Xiaoping Wan ◽  
Steven Poelzing ◽  
Eckhard Ficker ◽  
David S. Rosenbaum
Keyword(s):  
Left Ventricle ◽  
Gap Junction ◽  
Conduction Velocity ◽  
Velocity Dispersion ◽  
Expression Patterns ◽  
Fold Increase ◽  
Ventricular Wall ◽  
Cx43 Expression ◽  
Electrophysiological Properties ◽  
Junction Protein

Gap junctions are critical to maintaining synchronized impulse propagation and repolarization. Heterogeneous expression of the principal ventricular gap junction protein connexin43 (Cx43) is associated with action potential duration (APD) dispersion across the anterior ventricular wall. Little is known about Cx43 expression patterns and their disparate impact on regional electrophysiology throughout the heart. We aimed to determine whether the anterior and posterior regions of the heart are electrophysiologically distinct. Multisegment, high-resolution optical mapping was performed in canine wedge preparations harvested separately from the anterior left ventricle (aLV; n = 8) and posterior left ventricle (pLV; n = 8). Transmural APD dispersion was significantly greater on the aLV than the pLV (45 ± 13 vs. 26 ± 8.0 ms; P < 0.05). Conduction velocity dispersion was also significantly higher ( P < 0.05) across the aLV (39 ± 7%) than the pLV (16 ± 3%). Carbenoxolone perfusion significantly enhanced APD and conduction velocity dispersion on the aLV (by 1.53-fold and 1.36-fold, respectively), but not the pLV (by 1.27-fold and 1.2-fold, respectively), and produced a 4.2-fold increase in susceptibility to inducible arrhythmias in the aLV. Confocal immunofluorescence microscopy revealed significantly ( P < 0.05) greater transmural dispersion of Cx43 expression on the aLV (44 ± 10%) compared with the pLV wall (8.3 ± 0.7%), suggesting that regional expression of Cx43 expression patterns may account for regional electrophysiological differences. Computer simulations affirmed that localized uncoupling at the epicardial-midmyocardial interface is sufficient to produce APD gradients observed on the aLV. These data demonstrate that the aLV and pLV differ importantly with respect to their electrophysiological properties and Cx43 expression patterns. Furthermore, local underexpression of Cx43 is closely associated with transmural electrophysiological heterogeneity on the aLV. Therefore, regional and transmural heterogeneous Cx43 expression patterns may be an important mechanism underlying arrhythmia susceptibility, particularly in disease states where gap junction expression is altered.

scholarly journals Remodeling of the peripheral cardiac conduction system in response to pressure overload

2012 ◽  
Vol 302 (8) ◽  
pp. H1712-H1725 ◽  
Author(s):  
Brett S. Harris ◽  
Catalin F. Baicu ◽  
Nicole Haghshenas ◽  
Harinath Kasiganesan ◽  
Dimitri Scholz ◽  
...  
Keyword(s):  
Ion Channel ◽  
Gap Junction ◽  
Normal Sinus Rhythm ◽  
Expression Patterns ◽  
Pressure Overload ◽  
Left Ventricular ◽  
Conduction System ◽  
Cardiac Conduction ◽  
Hypertrophic Growth ◽  
Transaortic Constriction

How chronic pressure overload affects the Purkinje fibers of the ventricular peripheral conduction system (PCS) is not known. Here, we used a connexin (Cx)40 knockout/enhanced green fluorescent protein knockin transgenic mouse model to specifically label the PCS. We hypothesized that the subendocardially located PCS would remodel after chronic pressure overload and therefore analyzed cell size, markers of hypertrophy, and PCS-specific Cx and ion channel expression patterns. Left ventricular hypertrophy with preserved systolic function was induced by 30 days of surgical transaortic constriction. After transaortic constriction, we observed that PCS cardiomyocytes hypertrophied by 23% ( P < 0.05) and that microdissected PCS tissue exhibited upregulated markers of hypertrophy. PCS cardiomyocytes showed a 98% increase in the number of Cx40-positive gap junction particles, with an associated twofold increase in gene expression ( P < 0.05). We also identified a 50% reduction in Cx43 gap junction particles located at the interface between PCS cardiomyocytes and the working cardiomyocyte. In addition, we measured a fourfold increase of an ion channel, hyperpolarization-activated cyclic nucleotide-gated channel (HCN)4, throughout the PCS ( P < 0.05). As a direct consequence of PCS remodeling, we found that pressure-overloaded hearts exhibited marked changes in ventricular activation patterns during normal sinus rhythm. These novel findings characterize PCS cardiomyocyte remodeling after chronic pressure overload. We identified significant hypertrophic growth accompanied by modified expression of Cx40, Cx43, and HCN4 within PCS cardiomyocytes. We found that a functional outcome of these changes is a failure of the PCS to activate the ventricular myocardium normally. Our findings provide a proof of concept that pressure overload induces specific cellular changes, not just within the working myocardium but also within the specialized PCS.

Abstract 16378: Increased Extracellular Sodium and Calcium Modify the Extracellular Potassium and Cardiac Conduction Velocity Relationship in a Langendorff-perfused Guinea Pig Heart

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
David Ryan King ◽  
Michael ENTZ ◽  
Grace Blair ◽  
Ian Crandell ◽  
Alexandra Hanlon ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Conduction Velocity ◽  
Cardiac Conduction ◽  
Extracellular Potassium ◽  
Guinea Pig Heart ◽  
Conduction Loss ◽  
High K ◽  
Velocity Relationship ◽  
Severe Hyperkalemia ◽  
Extracellular Sodium

Background: Previous studies have demonstrated a biphasic relationship between extracellular potassium (K o ) and cardiac conduction velocity (CV). With moderate hyperkalemia, CV increases in what is referred to as supernormal conduction, but further increases in K o lead to severe conduction slowing and asystole. We recently demonstrated that altering extracellular sodium (Na o ) and extracellular calcium (Ca o ) modulates CV dependence on gap junctions (GJs). We have also shown that increasing Na o and Ca o can attenuate conduction loss caused by global ischemia ischemia. The purpose of this study was to determine if increasing Na o and Ca o would alter the K o -CV relationship and preserve CV at high K o . Hypothesis: Increasing Na o and Ca o will mitigate conduction slowing and the incidence of asystole associated with severe hyperkalemia in conditions of both normal and uncoupled GJs. Methods: Langendorff-perfused guinea pig hearts were optically mapped to measure CV. Na o was set to 145 or155mM and Ca o to 1.25 or 2.0mM. K o was varied from 4.6, 6.4, 8, to 10 mM in each experiment. Perfusion order was blinded and randomized. GJs were inhibited using carbenoxolone. Results: A biphasic K o -CV relationship was observed under all conditions. Maximum CV was achieved at either 6.4 or 8.0mM K o followed by a decrease in CV with increased K o . Importantly, the degree of CV slowing in the presence of 10mM K o was significantly reduced with the 155mM Na o / 2.0mM Ca o perfusate compared to all other Na o /Ca o combinations. Carbenoxolone reduced CV across all K o , but did not alter the K o -CV relationship. With 145mM Na o / 1.25mM Ca o , all hearts became asystolic at K o =10.0mM. Increasing Na o and Ca o significantly reduced the incidence of asystole at K o =10.0mM. Conclusions: Elevating Na o and Ca o preserves CV during severe hyperkalemia with or without strong GJ coupling. Increasing Na o and Ca o significantly reduces the incidence of asystole during severe hyperkalemia. These data suggest that non-linear and combinatorial effects of sodium, calcium, and GJ uncoupling can differentially modulate cardiac conduction during hyperkalemic perfusion. These results have important implications for cardioplegic arrest and ischemic heart disease when potassium and calcium homeostasis are disrupted.

Effect of Contraceptive Steroids on the Endometrium of Guinea Pig: SEM study

1977 ◽  
Vol 35 ◽  
pp. 668-669
Author(s):  
Mai M. Said ◽  
Ramesh K. Nayak ◽  
Randall E. McCoy
Keyword(s):  
Guinea Pig ◽  
Reproductive Tract ◽  
Three Dimensional ◽  
Female Reproductive Tract ◽  
Human Female ◽  
Surface Ultrastructure ◽  
Transmission Electron ◽  
Sem Study ◽  
Uterine Mucosa ◽  
Group 1

Burgos and Wislocki described changes in the mucosa of the guinea pig uterus, cervix and vagina during the estrous cycle investigated by transmission electron microscopy. More recently, Moghissi and Reame reported the effects of progestational agents on the human female reproductive tract. They found drooping and shortening of cilia in norgestrel and norethindrone- treated endometria. To the best of our knowledge, no studies concerning the effects of mestranol and norethindrone given concurrently on the three-dimensional surface features on the uterine mucosa of the guinea pig have been reported. The purpose of this study was to determine the effect of mestranol and norethindrone on surface ultrastructure of guinea pig uterus by SEM.Seventy eight animals were used in this study. They were allocated into two groups. Group 1 (20 animals) was injected intramuscularly 0.1 ml vegetable oil and served as controls.

Cell Reactivity Pattern of the Guinea Pig Cecal Mucosa Evidenced by the ZIO Technique

1982 ◽  
Vol 40 ◽  
pp. 50-51
Author(s):  
Juan Mora-Galindo ◽  
Jorge Arauz-Contreras
Keyword(s):  
Guinea Pig ◽  
Phase Contrast ◽  
Osmium Tetroxide ◽  
Cell Types ◽  
Cell Reactivity ◽  
Transmission Electron ◽  
Neural Tissues ◽  
Maturation Stages ◽  
Zinc Iodide ◽  
Cecal Mucosa

The zinc iodide-osmium tetroxide (ZIO) technique is presently employed to study both, neural and non neural tissues. Precipitates depends on cell types and possibly cell metabol ism as well.Guinea pig cecal mucosa, already known to be composed of epithelium with cells at different maturation stages and lamina propria which i s formed by morphologically and functionally heterogeneous cell population, was studied to determine the pat tern of ZIO impregnation. For this, adult Guinea pg cecal mucosa was fixed with buffered 1.2 5% g 1 utara 1 dehyde before incubation with ZIO for 16 hours, a t 4°C in the dark. Further steps involved a quick sample dehydration in graded ethanols, embedding in Epon 812 and sectioning to observe the unstained material under a phase contrast light microscope (LM) and a transmission electron microscope (TEM).

scholarly journals Transforming growth factor-β1-induced N-cadherin drives cell–cell communication through connexin43 in osteoblast lineage

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Yueyi Yang ◽  
Wenjing Liu ◽  
JieYa Wei ◽  
Yujia Cui ◽  
Demao Zhang ◽  
...  
Keyword(s):  
Growth Factor ◽  
Gap Junction ◽  
Cell Line ◽  
Transforming Growth Factor ◽  
Transforming Growth Factor Β1 ◽  
Cx43 Expression ◽  
Mc3t3 Cell ◽  
Primary Osteoblasts ◽  
Tgf Β1 ◽  
Cell Cell

AbstractGap junction (GJ) has been indicated to have an intimate correlation with adhesion junction. However, the direct interaction between them partially remains elusive. In the current study, we aimed to elucidate the role of N-cadherin, one of the core components in adhesion junction, in mediating connexin 43, one of the functional constituents in gap junction, via transforming growth factor-β1(TGF-β1) induction in osteoblasts. We first elucidated the expressions of N-cadherin induced by TGF-β1 and also confirmed the upregulation of Cx43, and the enhancement of functional gap junctional intercellular communication (GJIC) triggered by TGF-β1 in both primary osteoblasts and MC3T3 cell line. Colocalization analysis and Co-IP experimentation showed that N-cadherin interacts with Cx43 at the site of cell–cell contact. Knockdown of N-cadherin by siRNA interference decreased the Cx43 expression and abolished the promoting effect of TGF-β1 on Cx43. Functional GJICs in living primary osteoblasts and MC3T3 cell line were also reduced. TGF-β1-induced increase in N-cadherin and Cx43 was via Smad3 activation, whereas knockdown of Smad3 signaling by using siRNA decreased the expressions of both N-cadherin and Cx43. Overall, these data indicate the direct interactions between N-cadherin and Cx43, and reveal the intervention of adhesion junction in functional gap junction in living osteoblasts.

Phosphorylation of connexin 43 induced by traumatic brain injury promotes exosome release

2018 ◽  
Vol 119 (1) ◽  
pp. 305-311 ◽  
Author(s):  
Wei Chen ◽  
Yijun Guo ◽  
Wenjin Yang ◽  
Lei Chen ◽  
Dabin Ren ◽  
...  
Keyword(s):  
Traumatic Brain Injury ◽  
Brain Injury ◽  
Gap Junction ◽  
Connexin 43 ◽  
Hippocampal Slices ◽  
Long Term Potentiation ◽  
Cx43 Expression ◽  
Term Potentiation ◽  
Junction Protein

Traumatic brain injury (TBI) caused by the external force leads to the neuronal dysfunction and even death. TBI has been reported to significantly increase the phosphorylation of glial gap junction protein connexin 43 (Cx43), which in turn propagates damages into surrounding brain tissues. However, the neuroprotective and anti-apoptosis effects of glia-derived exosomes have also been implicated in recent studies. Therefore, we detected whether TBI-induced phosphorylation of Cx43 would promote exosome release in rat brain. To generate TBI model, adult male Sprague-Dawley rats were subjected to lateral fluid percussion injury. Phosphorylated Cx43 protein levels and exosome activities were quantified using Western blot analysis following TBI. Long-term potentiation (LTP) was also tested in rat hippocampal slices. TBI significantly increased the phosphorylated Cx43 and exosome markers expression in rat ipsilateral hippocampus, but not cortex. Blocking the activity of Cx43 or ERK, but not JNK, significantly suppressed TBI-induced exosome release in hippocampus. Furthermore, TBI significantly inhibited the induction of LTP in hippocampal slices, which could be partially but significantly restored by pretreatment with exosomes. The results imply that TBI-activated Cx43 could mediate a nociceptive effect by propagating the brain damages, as well as a neuroprotective effect by promoting exosome release. NEW & NOTEWORTHY We have demonstrated in rat traumatic brain injury (TBI) models that both phosphorylated connexin 43 (p-Cx43) expression and exosome release were elevated in the hippocampus following TBI. The promoted exosome release depends on the phosphorylation of Cx43 and requires ERK signaling activation. Exosome treatment could partially restore the attenuated long-term potentiation. Our results provide new insight for future therapeutic direction on the functional recovery of TBI by promoting p-Cx43-dependent exosome release but limiting the gap junction-mediated bystander effect.

scholarly journals Decreased connexin43 expression in the mouse heart potentiates pacing-induced remodeling of repolarizing currents

2008 ◽  
Vol 295 (5) ◽  
pp. H1905-H1916 ◽  
Author(s):  
Andrianos Kontogeorgis ◽  
Xiaodong Li ◽  
Eunice Y. Kang ◽  
Jonathan E. Feig ◽  
Marc Ponzio ◽  
...  
Keyword(s):  
Gap Junction ◽  
Ventricular Myocytes ◽  
Critical Role ◽  
Mouse Heart ◽  
Wild Type ◽  
Short Term ◽  
Wild Type Littermate ◽  
Cx43 Expression ◽  
Significant Prolongation ◽  
Electrophysiological Effects

Gap junction redistribution and reduced expression, a phenomenon termed gap junction remodeling (GJR), is often seen in diseased hearts and may predispose toward arrhythmias. We have recently shown that short-term pacing in the mouse is associated with changes in connexin43 (Cx43) expression and localization but not with increased inducibility into sustained arrhythmias. We hypothesized that short-term pacing, if imposed on murine hearts with decreased Cx43 abundance, could serve as a model for evaluating the electrophysiological effects of GJR. We paced wild-type (normal Cx43 abundance) and heterozygous Cx43 knockout (Cx43+/−; 66% mean reduction in Cx43) mice for 6 h at 10–15% above their average sinus rate. We investigated the electrophysiological effects of pacing on the whole animal using programmed electrical stimulation and in isolated ventricular myocytes with patch-clamp studies. Cx43+/− myocytes had significantly shorter action potential durations (APD) and increased steady-state ( Iss) and inward rectifier ( IK1) potassium currents compared with those of wild-type littermate cells. In Cx43+/− hearts, pacing resulted in a significant prolongation of ventricular effective refractory period and APD and significant diminution of Iss compared with unpaced Cx43+/− hearts. However, these changes were not seen in paced wild-type mice. These data suggest that Cx43 abundance plays a critical role in regulating currents involved in myocardial repolarization and their response to pacing. Our study may aid in understanding how dyssynchronous activation of diseased, Cx43-deficient myocardial tissue can lead to electrophysiological changes, which may contribute to the worsened prognosis often associated with pacing in the failing heart.

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