Gap junction formation and regulation in myometrium

1980 ◽  
Vol 239 (5) ◽  
pp. C217-C228 ◽  
Author(s):  
R. E. Garfield ◽  
D. Merrett ◽  
A. K. Grover
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
High Frequency ◽  
Actinomycin D ◽  
Low Frequency ◽  
Synthesis Inhibitor ◽  
Pregnant Rats ◽  
Junction Formation ◽  
Prostacyclin Analog

Myometrial tissues from pregnant rats were examined by electron microscopy for the presence of gap junctions after incubation in vitro with a variety of agents. Gap junctions were present in low frequency or absent prior to incubation in vitro. The junctions were present in control tissues in high frequency after 48 h incubation. The addition of cycloheximide or actinomycin D inhibited the incorporation of [3H]leucine into TCA-precipitable proteins and prevented gap junction formation. A prostacyclin analog (carbacyclin), a thromboxane synthesis inhibitor, and indomethacin also prevented gap junction formation. Oxytocin had no effect on gap junction formation but isoxsuprine decreased their number and increased their size. Isoxsuprine and isoproterenol also produced electron opaque crystals associated with the gap junctions. Dibutyryl cAMP treatment but not monobutyryl cGMP also increased the size of gap junctions. Based upon this and previous studies, we propose at least four sites for regulation of gap junctions and possible control of labor.

Control of gap junction formation in canine trachea by arachidonic acid metabolites

1986 ◽  
Vol 250 (3) ◽  
pp. C495-C505 ◽  
Author(s):  
R. Agrawal ◽  
E. E. Daniel
Keyword(s):  
Arachidonic Acid ◽  
Gap Junctions ◽  
Gap Junction ◽  
Direct Effects ◽  
Leukotriene C4 ◽  
Lipoxygenase Pathway ◽  
Junction Formation ◽  
Acid Metabolites ◽  
Pg E2

This study examined whether the synthesis of the metabolites of arachidonic acid (AA) was involved in gap junction formation by 4-aminopyridine (4-AP) treatment in vitro in canine trachealis. Studies were made of the effects on gap junction formation of putative inhibitors of the cyclooxygenase and of both this and the lipoxygenase pathway of AA metabolism and the direct effects of prostaglandins (PG) E2 and I2. The number of gap junctions of similar size was increased after brief exposure to 4-AP. After indomethacin (IDM), 4-AP treatment decreased the number of gap junctions but did not affect their size. Pretreatment with 5,8,11,14-eicosatetraynoic acid or nordihydroguiaretic acid, putative inhibitors of cyclooxygenase and lipoxygenase enzymes, inhibited both the 4-AP-induced increase and decrease in the number of gap junctions. FPL 55712, a putative antagonist of leukotriene C4, did not alter either the number or the size of gap junctions when added alone or in combination with IDM. AA alone increased the number of gap junctions, but after IDM, AA decreased the number of gap junctions compared with the controls. Incubation of trachealis strips in vitro for 30 min with PGE2 increased the number of gap junctions by about threefold along with an increase in the size of the gap junctions. Similar incubation with PGI2, however, increased the number of gap junctions by approximately 60% without any change in the size. In the course of some control experiments, an interaction between carbachol and alcohol was observed such that alcohol caused an IDM-sensitive relaxation of carbachol-induced contractions, which was not observed when serotonin was the contractile agent. These results strongly suggest that PGE2 and PGI2 increase the formation of gap junctions in canine trachealis and that these prostanoids are released by 4-AP treatment. Leukotrienes may also be inhibitory in the formation of gap junctions, but FPL 55712 did not affect either the increase or the decrease in gap junctions after 4-AP.

Possible role of gap junctions in activation of myometrium during parturition

1978 ◽  
Vol 235 (5) ◽  
pp. C168-C179 ◽  
Author(s):  
R. E. Garfield ◽  
S. M. Sims ◽  
M. S. Kannan ◽  
E. E. Daniel
Keyword(s):  
Smooth Muscle ◽  
Gap Junctions ◽  
Freeze Fracture ◽  
Normal Pregnancy ◽  
Pregnant Rats ◽  
Junction Formation ◽  
Synchronous Contraction ◽  
Do So

Gap junctions between smooth muscle cells of the myometrium of pregnant rats were found only immediately prior to, during and immediately after parturition by quantitative thin-section and freeze-fracture microscopy. Ovariectomy of 16- to 17-days-pregnant rats resulted in premature termination of pregnancy and the appearance of gap junctions. Methods that prolonged normal pregnancy in rats or maintained pregnancy in ovariectomized animals (progesterone treatment) prevented the appearance of gap junctions. Gap junctions formed in tissues incubated for 24--96 h in vitro without any hormonal influence. We propose that gap junctions are essential for normal labor and delivery for synchronous contraction of the muscle of the uterus. We present a model for control of parturition that may apply to other animals including humans. The model proposes: 1) the possible roles progesterone, prostaglandins, or estrogens may play in initiating gap-junction formation; 2) that the formation of gap junctions is a necessary step in activation of the myometrium leading to labor; and 3) that agents used to stimulate or inhibit labor may do so by affecting gap junctions.

Rapid de novo formation of gap junctions between insect hemocytes in vitro: a freeze-fracture, dye- transfer and patch-clamp study

1993 ◽  
Vol 104 (3) ◽  
pp. 763-772 ◽  
Author(s):  
D. Churchill ◽  
S. Coodin ◽  
R. R. Shivers ◽  
S. Caveney
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Periplaneta Americana ◽  
Single Channel ◽  
De Novo ◽  
Freeze Fracture ◽  
Cell Contact ◽  
Junction Formation ◽  
Insect Hemocytes

Gap junctions form between insect hemocytes (blood cells) when they encapsulate foreign objects in the hemocoel (body cavity). In this study we show that hemocytes from cockroach (Periplaneta americana) form gap-junctions rapidly in vitro. Freeze-fracture replicas of hemocyte aggregates fixed 5 minutes after bleeding contain gap-junctional plaques. Dye passage was detected between carboxyfluorescein diacetate- labelled and unlabelled hemocytes within 3 minutes of bleeding, when the cells made contact as they flattened rapidly onto coverslips. When double whole-cell voltage-clamp was used to measure gap-junction formation between cells which were pushed together, electrical coupling was detected within one second of cell-cell contact. To prevent extensive flattening, cells were plated onto lipophorin-coated coverslips. Junctional conductance increased in staircase fashion with steps corresponding to an average single channel conductance of 345 pS. Assuming all channels to have this conductance, the maximal accretion rate of channels to the growing junction was one channel per second. Junctional currents and dye-coupling were detected in the absence of Ca2+, indicating that involvement of Ca2+-dependent adhesion molecules is not a prerequisite for gap-junction formation in hemocytes. Hemocytes from distantly related insects (cockroach and moth) form functional gap junctions with each other, suggesting sequence homology among gap- junction proteins in insects. The function of rapid gap-junction formation between hemocytes during encapsulation and wound healing in vivo are discussed.

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.

Sharp Wave-Like Activity in the Hippocampus In Vitro in Mice Lacking the Gap Junction Protein Connexin 36

2003 ◽  
Vol 89 (4) ◽  
pp. 2046-2054 ◽  
Author(s):  
Isabel Pais ◽  
Sheriar G. Hormuzdi ◽  
Hannah Monyer ◽  
Roger D. Traub ◽  
Ian C. Wood ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Frequency Oscillation ◽  
Connexin 36 ◽  
Sharp Wave ◽  
Bath Application ◽  
Junction Protein ◽  
Gap Junction Protein ◽  
Electrical Signaling

Bath application of kainate (100–300 nM) induced a persistent gamma-frequency (30–80 Hz) oscillation that could be recorded in stratum radiatum of the CA3 region in vitro. We have previously described that in knockout mice lacking the gap junction protein connexin 36 (Cx36KO), γ-frequency oscillations are reduced but still present. We now demonstrate that in the Cx36KO mice, but not in wild-type (WT), large population field excitatory postsynaptic potentials, or sharp wave-burst discharges, also occurred during the on-going γ-frequency oscillation. These spontaneous burst discharges were not seen in WT mice. Burst discharges in the Cx36KO mice occurred with a mean frequency of 0.23 ± 0.11 Hz and were accompanied by a series of fast (approximately 60–115 Hz) population spikes or “ripple” oscillations in many recordings. Intracellular recordings from CA3 pyramidal cells showed that the burst discharges consisted of a depolarizing response and presumed coupling potentials (spikelets) could occasionally be seen either before or during the burst discharge. The burst discharges occurring in Cx36KO mice were sensitive to gap junctions blockers as they were fully abolished by carbenoxolone (200 μM). In control mice we made several attempts to replicate this pattern of sharp wave activity/ripples occurring with the on-going kainate-evoked γ-frequency oscillation by manipulating synaptic and electrical signaling. Partial disruption of inhibition, in control slices, by bath application of the γ-aminobutyric acid-A (GABAA) receptor antagonist bicuculline (1–4 μM) completely abolished all γ-frequency activity before any burst discharges occurred. Increasing the number of open gap junctions in control slices by using trimethylamine (TMA; 2–10 mM), in conjunction with kainate, failed to elicit any sharp wave bursts or fast ripples. However, bath application of the potassium channel blocker 4-aminopyridine (4-AP; 20–80 μM) produced a pattern of activity in control mice (13/16 slices), consisting of burst discharges occurring in conjunction with kainate-evoked γ-frequency oscillations, that was similar to that seen in Cx36KO mice. In a few cases ( n = 9) the burst discharges were accompanied by fast ripple oscillations. Carbenoxolone also fully blocked the 4-AP-evoked burst discharges ( n = 5). Our results show that disruption of electrical signaling in the interneuronal network can, in the presence of kainate, lead to the spontaneous generation of sharp wave/ripple activity similar to that observed in vivo. This suggests a complex role for electrically coupled interneurons in the generation of hippocampal network activity.

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.

Neuronal Aggregate Formation Underlies Spatiotemporal Dynamics of Nonsynaptic Seizure Initiation

2003 ◽  
Vol 89 (4) ◽  
pp. 2330-2333 ◽  
Author(s):  
Marom Bikson ◽  
John E. Fox ◽  
John G. R. Jefferys
Keyword(s):  
Synaptic Transmission ◽  
Gap Junctions ◽  
High Frequency ◽  
Formation Rate ◽  
Simultaneous Recording ◽  
Aggregate Formation ◽  
Seizure Onset ◽  
Electrographic Seizures ◽  
High Frequency Activity

High-frequency activity often precedes seizure onset. We found that electrographic seizures, induced in vitro using the low-Ca2+ model, start with high-frequency (>150 Hz) activity that then decreases in frequency while increasing in amplitude. Multichannel and unit recordings showed that the mechanism of this transition was the progressive formation of larger neuronal aggregates. Thus the apparenthigh-frequency activity, at seizure onset, can reflect the simultaneous recording of several slower firing aggregates. Aggregate formation rate can be accelerated by reducing osmolarity. Because synaptic transmission is blocked when extracellular Ca2+ is reduced, nonsynaptic mechanisms (gap junctions, field effects) must be sufficient for aggregate formation and recruitment.

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.

Effects of inactivation of oxytocin receptor and inhibition of prostaglandin synthesis on uterine oxytocin receptor and gap junction formation and labor in the rat

1991 ◽  
Vol 69 (9) ◽  
pp. 1262-1267 ◽  
Author(s):  
W. Y. Chan ◽  
Irene Berezin ◽  
E. E. Daniel ◽  
K. C. Russell ◽  
Victor J. Hruby
Keyword(s):  
Gap Junction ◽  
Naproxen Sodium ◽  
Critical Role ◽  
Treated Group ◽  
Oxytocin Receptor ◽  
Prostaglandin Synthesis ◽  
Pregnant Rats ◽  
Junction Formation ◽  
Inhibition Of Prostaglandin Synthesis ◽  
Oxytocin Antagonist

Normal term labor is associated with a surge in myometrial oxytocin receptor formation and gap junction development. We have previously shown that inhibition of prostaglandin synthesis by naproxen sodium, 2.0 mg/day, suppressed oxytocin receptor formation but not gap junction formation and prolonged gestation. In this study, we investigated the effects of a specific oxytocin antagonist on oxytocin receptor formation, gap junction formation, and labor in the rat. [Pen1Phe(Me)2,Thr4,Orn8]oxytocin, a specific oxytocin antagonist, was infused subcutaneously during the last 3 days of pregnancy at 300 μg/day. Measurements of myometrial oxytocin receptor concentrations and gap junction formation on days 21 and 22 and days 22–23 (in labor) pregnant uteri showed no significant differences in the Bmax and Kd values between the control and the treated group. Gestation period was not prolonged by the oxytocin antagonist. However, in a separate group of day 23 pregnant rats, the uterine contractile response to 60 mU of oxytocin i.v. was found completely blocked by 10 μg of the oxytocin antagonist. These findings suggest that although functional oxytocin receptors did not appear to be essential for the initiation of labor, oxytocin antagonists may still be effective in the prevention of premature contractions. We also examined the effects of a higher dose of naproxen sodium, 5.0 mg/day, on gap junction formation. At this dose, naproxen sodium suppressed both oxytocin receptor and gap junction formation, prolonged gestation, and delayed parturition by 24 h or longer. Prostaglandin appears to be an important regulator or mediator of oxytocin receptor and gap junction formation and plays a critical role in the initiation of labor.Key words: oxytocin, prostaglandin, oxytocin receptor, gap junction, labor.

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