scholarly journals Electromechanical Coupling between Skeletal and Cardiac Muscle

2000 ◽  
Vol 149 (3) ◽  
pp. 731-740 ◽  
Author(s):  
Hans Reinecke ◽  
Glen H. MacDonald ◽  
Stephen D. Hauschka ◽  
Charles E. Murry
Keyword(s):  
Skeletal Muscle ◽  
Gap Junctions ◽  
Cardiac Muscle ◽  
Gap Junction ◽  
Electromechanical Coupling ◽  
Skeletal Myoblasts ◽  
Adult Cardiomyocytes ◽  
Synchronous Contraction ◽  
Skeletal Myotubes

Skeletal myoblasts form grafts of mature muscle in injured hearts, and these grafts contract when exogenously stimulated. It is not known, however, whether cardiac muscle can form electromechanical junctions with skeletal muscle and induce its synchronous contraction. Here, we report that undifferentiated rat skeletal myoblasts expressed N-cadherin and connexin43, major adhesion and gap junction proteins of the intercalated disk, yet both proteins were markedly downregulated after differentiation into myo-tubes. Similarly, differentiated skeletal muscle grafts in injured hearts had no detectable N-cadherin or connexin43; hence, electromechanical coupling did not occur after in vivo grafting. In contrast, when neonatal or adult cardiomyocytes were cocultured with skeletal muscle, ∼10% of the skeletal myotubes contracted in synchrony with adjacent cardiomyocytes. Isoproterenol increased myotube contraction rates by 25% in coculture without affecting myotubes in monoculture, indicating the cardiomyocytes were the pacemakers. The gap junction inhibitor heptanol aborted myotube contractions but left spontaneous contractions of individual cardiomyocytes intact, suggesting myotubes were activated via gap junctions. Confocal microscopy revealed the expression of cadherin and connexin43 at junctions between myotubes and neonatal or adult cardiomyocytes in vitro. After microinjection, myotubes transferred dye to neonatal cardiomyocytes via gap junctions. Calcium imaging revealed synchronous calcium transients in cardiomyocytes and myotubes. Thus, cardiomyocytes can form electromechanical junctions with some skeletal myotubes in coculture and induce their synchronous contraction via gap junctions. Although the mechanism remains to be determined, if similar junctions could be induced in vivo, they might be sufficient to make skeletal muscle grafts beat synchronously with host myocardium.

scholarly journals Two Drosophila Innexins Are Expressed in Overlapping Domains and Cooperate to Form Gap-Junction Channels

2000 ◽  
Vol 11 (7) ◽  
pp. 2459-2470 ◽  
Author(s):  
Lucy A. Stebbings ◽  
Martin G. Todman ◽  
Pauline Phelan ◽  
Jonathan P. Bacon ◽  
Jane A. Davies
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Ectopic Expression ◽  
In Vivo Studies ◽  
Electrophysiological Properties ◽  
Gap Junction Channels ◽  
Overlapping Domains ◽  
In Vitro Data

Members of the innexin protein family are structural components of invertebrate gap junctions and are analogous to vertebrate connexins. Here we investigate two Drosophila innexin genes,Dm-inx2 and Dm-inx3 and show that they are expressed in overlapping domains throughout embryogenesis, most notably in epidermal cells bordering each segment. We also explore the gap-junction–forming capabilities of the encoded proteins. In pairedXenopus oocytes, the injection of Dm-inx2mRNA results in the formation of voltage-sensitive channels in only ∼ 40% of cell pairs. In contrast, Dm-Inx3 never forms channels. Crucially, when both mRNAs are coexpressed, functional channels are formed reliably, and the electrophysiological properties of these channels distinguish them from those formed by Dm-Inx2 alone. We relate these in vitro data to in vivo studies. Ectopic expression ofDm-inx2 in vivo has limited effects on the viability ofDrosophila, and animals ectopically expressingDm-inx3 are unaffected. However, ectopic expression of both transcripts together severely reduces viability, presumably because of the formation of inappropriate gap junctions. We conclude that Dm-Inx2 and Dm-Inx3, which are expressed in overlapping domains during embryogenesis, can form oligomeric gap-junction channels.

scholarly journals Adhesive multiplicity in the interaction of embryonic fibroblasts and myoblasts with extracellular matrices.

1984 ◽  
Vol 99 (4) ◽  
pp. 1398-1404 ◽  
Author(s):  
C Decker ◽  
R Greggs ◽  
K Duggan ◽  
J Stubbs ◽  
A Horwitz
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Muscle ◽  
Cardiac Fibroblasts ◽  
Cell Types ◽  
Extracellular Matrices ◽  
Common Denominator ◽  
Cell Matrix ◽  
Skeletal Myoblasts ◽  
A Cell ◽  
Cell Matrix Adhesion

Neff et al. (1982, J. Cell Biol., 95:654-666) have described a monoclonal antibody, CSAT, directed against a cell surface antigen that participates in the adhesion of skeletal muscle to extracellular matrices. We used the same antibody to compare and parse the determinants of adhesion and morphology on myogenic and fibrogenic cells. We report here that the antigen is present on skeletal and cardiac muscle and on tendon, skeletal, dermal, and cardiac fibroblasts; however, its contribution to their morphology and adhesion is different. The antibody produces large alterations in the morphology and adhesion of skeletal myoblasts and tendon fibroblasts; in contrast, its effects on the cardiac fibroblasts are not readily detected. The effects of CSAT on the other cell types, i.e., dermal and skeletal fibroblasts, cardiac muscle, 5-bromodeoxyuridine-treated skeletal muscle, lie between these extremes. The effects of CSAT on the skeletal myoblasts depends on the calcium concentration in the growth medium and on the culture age. We interpret these differential responses to CSAT as revealing differences in the adhesion of the various cells to extracellular matrices. This interpretation is supported by parallel studies using quantitative assays of cell-matrix adhesion. The likely origin of these adhesive differences is the progressive display of different kinds of adhesion-related molecules and their organizational complexes on increasingly adhesive cells. The antigen to which CSAT is directed is present on all of the above cells and thus appears to be a lowest common denominator of their adhesion to extracellular matrices.

scholarly journals The Functional Implications of Endothelial Gap Junctions and Cellular Mechanics in Vascular Angiogenesis

Cancers ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 237 ◽  
Author(s):  
Takayuki Okamoto ◽  
Haruki Usuda ◽  
Tetsuya Tanaka ◽  
Koichiro Wada ◽  
Motomu Shimaoka
Keyword(s):  
Endothelial Cells ◽  
Cell Migration ◽  
Gap Junctions ◽  
Gap Junction ◽  
Cancer Cells ◽  
Tumor Development ◽  
Tube Formation ◽  
Cellular Mechanics

Angiogenesis—the sprouting and growth of new blood vessels from the existing vasculature—is an important contributor to tumor development, since it facilitates the supply of oxygen and nutrients to cancer cells. Endothelial cells are critically affected during the angiogenic process as their proliferation, motility, and morphology are modulated by pro-angiogenic and environmental factors associated with tumor tissues and cancer cells. Recent in vivo and in vitro studies have revealed that the gap junctions of endothelial cells also participate in the promotion of angiogenesis. Pro-angiogenic factors modulate gap junction function and connexin expression in endothelial cells, whereas endothelial connexins are involved in angiogenic tube formation and in the cell migration of endothelial cells. Several mechanisms, including gap junction function-dependent or -independent pathways, have been proposed. In particular, connexins might have the potential to regulate cell mechanics such as cell morphology, cell migration, and cellular stiffness that are dynamically changed during the angiogenic processes. Here, we review the implication for endothelial gap junctions and cellular mechanics in vascular angiogenesis.

pH Sensitivity of Non-Synaptic Field Bursts in the Dentate Gyrus

2000 ◽  
Vol 84 (2) ◽  
pp. 927-933 ◽  
Author(s):  
Jeffrey S. Schweitzer ◽  
Haiwei Wang ◽  
Zhi-Qi Xiong ◽  
Janet L. Stringer
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Granule Cell ◽  
Low Ph ◽  
Ph Sensitivity ◽  
Extracellular Ph ◽  
Granule Cell Layer ◽  
Ph Changes

Under conditions of low [Ca2+]o and high [K+]o, the rat dentate granule cell layer in vitro develops recurrent spontaneous prolonged field bursts that resemble an in vivo phenomenon called maximal dentate activation. To understand how pH changes in vivo might affect this phenomenon, the slices were exposed to different extracellular pH environments in vitro. The field bursts were highly sensitive to extracellular pH over the range 7.0–7.6 and were suppressed at low pH and enhanced at high pH. Granule cell resting membrane potential, action potentials, and postsynaptic potentials were not significantly altered by pH changes within the range that suppressed the bursts. The pH sensitivity of the bursts was not altered by pharmacologic blockade of N-methyl-d-aspartate (NMDA), non-NMDA, and GABAA receptors at concentrations of these agents sufficient to eliminate both spontaneous and evoked synaptic potentials. Gap junction patency is known to be sensitive to pH, and agents that block gap junctions, including octanol, oleamide, and carbenoxolone, blocked the prolonged field bursts in a manner similar to low pH. Perfusion with gap junction blockers or acidic pH suppressed field bursts but did not block spontaneous firing of single and multiple units, including burst firing. These data suggest that the pH sensitivity of seizures and epileptiform phenomena in vivo may be mediated in large part through mechanisms other than suppression of NMDA-mediated or other excitatory synaptic transmission. Alterations in electrotonic coupling via gap junctions, affecting field synchronization, may be one such process.

scholarly journals Gap junction internalization and processing in vivo: a 3D immuno-electron microscopy study

2020 ◽  
pp. jcs.252726
Author(s):  
Rachael P. Norris ◽  
Mark Terasaki
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Connexin 43 ◽  
New Technology ◽  
Cell Communication ◽  
Membrane Vesicles ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Annular Gap

Gap junctions have well-established roles in cell-cell communication by way of forming permeable intercellular channels. Less is understood about their internalization, which forms double membrane vesicles containing cytosol and membranes from another cell, called connexosomes or annular gap junctions. Here, we systematically investigated the fate of connexosomes in intact ovarian follicles. High pressure frozen, serial sectioned tissue was immunogold labeled for Connexin 43. Within a volume corresponding to ∼35 cells, every labeled structure was categorized and its surface area was measured. Measurements support the concept that multiple connexosomes form from larger invaginated gap junctions. Subsequently, the inner and outer membranes separate, Cx43 immunogenicity is lost from the outer membrane, and the inner membrane appears to undergo fission. One pathway for processing involves lysosomes, based on localization of Cathespin B to some processed connexosomes. In summary, this study demonstrates new technology for high-resolution analyses of gap junction processing.

scholarly journals Five-hour half-life of mouse liver gap-junction protein.

1981 ◽  
Vol 90 (2) ◽  
pp. 521-526 ◽  
Author(s):  
R F Fallon ◽  
D A Goodenough
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Half Life ◽  
Mouse Liver ◽  
Polyacrylamide Gels ◽  
Junction Protein ◽  
Gap Junction Protein ◽  
Polypeptide Band

The half-life of a gap-junction polypeptide band migrating at 21,000 Mr on SDS polyacrylamide gels isolated from mouse liver is measured to be 5 h. Two low-molecular wight bands, probably related to the 21,000 Mr material by proteolysis, have measured half-lives of 4.6 and 5.2 h. Gap junctions are labeled in vivo using the 14C-bicarbonate labeling procedure, followed by quantitative fluorography.

scholarly journals Fibroblast Growth Factor 4 Directs Gap Junction Expression in the Mesenchyme of the Vertebrate Limb Bud

1997 ◽  
Vol 138 (5) ◽  
pp. 1125-1137 ◽  
Author(s):  
H. Makarenkova ◽  
D.L. Becker ◽  
C. Tickle ◽  
A.E. Warner
Keyword(s):  
Growth Factor ◽  
Gap Junctions ◽  
Gap Junction ◽  
Fibroblast Growth Factor ◽  
Connexin 43 ◽  
Limb Bud ◽  
Functional Coupling ◽  
Fibroblast Growth ◽  
Mesenchyme Cells

Pattern in the developing limb depends on signaling by polarizing region mesenchyme cells, which are located at the posterior margin of the bud tip. Here we address the underlying cellular mechanisms. We show in the intact bud that connexin 43 (Cx43) and Cx32 gap junctions are at higher density between distal posterior mesenchyme cells at the tip of the bud than between either distal anterior or proximal mesenchyme cells. These gradients disappear when the apical ectodermal ridge (AER) is removed. Fibroblast growth factor 4 (FGF4) produced by posterior AER cells controls signaling by polarizing cells. We find that FGF4 doubles gap junction density and substantially improves functional coupling between cultured posterior mesenchyme cells. FGF4 has no effect on cultured anterior mesenchyme, suggesting that any effects of FGF4 on responding anterior mesenchyme cells are not mediated by a change in gap junction density or functional communication through gap junctions. In condensing mesenchyme cells, connexin expression is not affected by FGF4. We show that posterior mesenchyme cells maintained in FGF4 under conditions that increase functional coupling maintain polarizing activity at in vivo levels. Without FGF4, polarizing activity is reduced and the signaling mechanism changes. We conclude that FGF4 regulation of cell–cell communication and polarizing signaling are intimately connected.

Differential response of embryonic and fetal myoblasts to TGF beta: a possible regulatory mechanism of skeletal muscle histogenesis

Development ◽  
1994 ◽  
Vol 120 (4) ◽  
pp. 925-933 ◽  
Author(s):  
M.G. Cusella-De Angelis ◽  
S. Molinari ◽  
A. Le Donne ◽  
M. Coletta ◽  
E. Vivarelli ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Proximal Region ◽  
S Phase ◽  
Fiber Formation ◽  
Limb Bud ◽  
Tgf Beta ◽  
Heavy Chains ◽  
Skeletal Myoblasts ◽  
Brdu Labeling

Embryonic and fetal skeletal myoblasts were grown in culture in the presence of TGF beta. Under the conditions employed, TGF beta inhibited differentiation of fetal but not of embryonic myoblasts. To investigate the possible relevance of these data to skeletal muscle histogenesis in vivo, we studied the proliferation/differentiation state of mesodermal cells in the proximal region of the limb bud at the time of primary fiber formation. BrdU labeling and immunostaining for myosin heavy chains revealed that very few mesodermal cells enter the S phase of the cycle when differentiated primary fibers first appear. However, a few hours later, many cells in S phase surround newly formed muscle fibers, suggesting that the latter may be a source of mitogens for undifferentiated myoblasts. Co-culture experiments supported this hypothesis, showing that medium conditioned by fiber-containing explants can stimulate myoblast proliferation. Taken together these data suggested a possible mechanism for the regulation of muscle fiber formation. The model assumes that fibers form in the proximal region of the limb bud, where TGF beta is known to be present, and BrdU labeling experiments did not reveal cells in S phase. It is conceivable that non-dividing embryonic myoblasts (which do not respond to TGF beta) can undergo differentiation, while fetal myoblasts are inhibited by TGF beta. Once formed, primary fibers may stimulate a new wave of proliferation in fetal myoblasts, in order to expand the pool of cells needed to form secondary fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Decreased Fast Ripples in the Hippocampus of Rats with Spontaneous Recurrent Seizures Treated with Carbenoxolone and Quinine

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Consuelo Ventura-Mejía ◽  
Laura Medina-Ceja
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
High Frequency Oscillations ◽  
The Mean ◽  
Eeg Recordings ◽  
The Right ◽  
Spontaneous Recurrent Seizures

Background. In models of temporal lobe epilepsy and in patients with this pathology, high frequency oscillations called fast ripples (FRs, 250–600 Hz) can be observed. FRs are considered potential biomarkers for epilepsy and, in the light of manyin vitroandin silicostudies, we thought that electrical synapses mediated by gap junctions might possibly modulate FRsin vivo.Methods. Animals with spontaneous recurrent seizures induced by pilocarpine administration were implanted with movable microelectrodes in the right anterior and posterior hippocampus to evaluate the effects of gap junction blockers administered in the entorhinal cortex. The effects of carbenoxolone (50 nmoles) and quinine (35 pmoles) on the mean number of spontaneous FR events (occurrence of FRs), as well as on the mean number of oscillation cycles per FR event and their frequency, were assessed using a specific algorithm to analyze FRs in intracranial EEG recordings.Results. We found that these gap junction blockers decreased the mean number of FRs and the mean number of oscillation cycles per FR event in the hippocampus, both during and at different times after carbenoxolone and quinine administration.Conclusion. These data suggest that FRs may be modulated by gap junctions, although additional experimentsin vivowill be necessary to determine the precise role of gap junctions in this pathological activity associated with epileptogenesis.

scholarly journals Lmo7 is dispensable for skeletal muscle and cardiac function

2015 ◽  
Vol 309 (7) ◽  
pp. C470-C479 ◽  
Author(s):  
Dieu Hung Lao ◽  
Mary C. Esparza ◽  
Shannon N. Bremner ◽  
Indroneal Banerjee ◽  
Jianlin Zhang ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscular Dystrophy ◽  
Cardiac Function ◽  
Cardiac Muscle ◽  
Mapk Pathway ◽  
Mdx Mouse ◽  
Mdx Mice ◽  
Mouse Line

Emery-Dreifuss muscular dystrophy (EDMD) is a degenerative disease primarily affecting skeletal muscles in early childhood as well as cardiac muscle at later stages. EDMD is caused by a number of mutations in genes encoding proteins associated with the nuclear envelope (e.g., Emerin, Lamin A/C, and Nesprin). Recently, a novel protein, Lim-domain only 7 ( lmo7) has been reported to play a role in the molecular pathogenesis of EDMD. Prior in vitro and in vivo studies suggested the intriguing possibility that Lmo7 plays a role in skeletal or cardiac muscle pathophysiology. To further understand the in vivo role of Lmo7 in striated muscles, we generated a novel Lmo7-null ( lmo7−/−) mouse line. Using this mouse line, we examined skeletal and cardiac muscle physiology, as well as the role of Lmo7 in a model of muscular dystrophy and regeneration using the dystrophin-deficient mdx mouse model. Our results demonstrated that lmo7−/− mice had no abnormalities in skeletal muscle morphology, physiological function, or regeneration. Cardiac function was also unaffected. Moreover, we found that ablation of lmo7 in mdx mice had no effect on the observed myopathy and muscular regeneration exhibited by mdx mice. Molecular analyses also showed no changes in dystrophin complex factors, MAPK pathway components, and Emerin levels in lmo7 knockout mice. Taken together, we conclude that Lmo7 is dispensable for skeletal muscle and cardiac physiology and pathophysiology.

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