Xenopus oocyte K+ current. III. Phorbol esters and pH regulate current at gap junctions

1990 ◽  
Vol 259 (5) ◽  
pp. C792-C800 ◽  
Author(s):  
L. J. Greenfield ◽  
J. T. Hackett ◽  
J. Linden
Keyword(s):  
Gap Junctions ◽  
Phorbol Esters ◽  
Electrical Coupling ◽  
Follicle Cell ◽  
Follicle Cells ◽  
Acid Ph ◽  
Junctional Conductance ◽  
K Current ◽  
Gap Junctional ◽  
K Currents

Xenopus follicles consist of a single large oocyte surrounded by a monolayer of follicle cells attached to the oocyte by gap junctions. Adenosine 3',5'-cyclic monophosphate (cAMP) activates an outward K+ current which is completely abolished if follicle cells are removed or if phorbol esters (which have been reported to reduce gap junctional conductance) are added. In this study we show that phorbol esters do not reduce cAMP levels in follicles and that acid pH, another known stimulus for reducing gap junctional conductance, mimics the action of phorbol esters to inhibit the cAMP-stimulated K+ current. We also examined electrical coupling between oocytes of pairs of follicles placed in physical contact (across 2 oocyte-follicle cell and 1 follicle cell-follicle cell gap junction). Phorbol esters and acid pH (5.5-6.5) decreased electrical coupling without eliciting a shunt current, since slope conductance of current-voltage curves recorded during voltage clamp was simultaneously decreased. Increasing cAMP, which has been reported to enhance gap junctional conductance in mammalian cells, increased slope conductance without decreasing electrical coupling between pairs of follicles. The data suggest that cAMP increases and phorbol esters and acid pH decrease K+ currents at least in part by effects on gap junctions. The effects of phorbol esters and acid pH to reduce electrical coupling between oocytes cannot be due to blockade of K+ channels, since such an action would increase electrical coupling (as verified by computer simulations). These findings are consistent with the idea that cAMP-activated K+ currents originate in follicle cells and are communicated to the oocyte via gap junctions.

Xenopus oocyte K+ current. I. FSH and adenosine stimulate follicle cell-dependent currents

1990 ◽  
Vol 259 (5) ◽  
pp. C775-C783 ◽  
Author(s):  
L. J. Greenfield ◽  
J. T. Hackett ◽  
J. Linden
Keyword(s):  
Protein Kinase ◽  
Gap Junctions ◽  
Adenylyl Cyclase ◽  
Follicle Cell ◽  
Follicle Cells ◽  
Dependent Protein Kinase ◽  
Camp Dependent Protein Kinase ◽  
Large Oocyte ◽  
K Current ◽  
Dependent Protein

Ovarian follicles of Xenopus laevis frogs consist of a single large oocyte surrounded by follicle cells attached to the oocyte by gap junctions. Adenosine has been found to activate an outward K+ current in follicles. This response is reduced by microinjection of protein kinase inhibitor (PKI), suggesting that adenosine 3',5'-cyclic monophosphate (cAMP) mediates the response. To investigate this further, we verified previous studies that indicate that several methods of elevating cAMP in follicles activate hyperpolarizing outward currents. The potency of two adenosine analogues to hyperpolarize follicles, 5'-N-ethylcarboxamidoadenosine (NECA) greater than cyclopentyladenosine, is indicative of A2 receptors that are characteristically coupled to adenylyl cyclase. We also report for the first time that another stimulator of adenylyl cyclase, follicle-stimulating hormone (FSH), also induces a hyperpolarizing current in follicles which is carried by K+ and attenuated by injection of PKI. We used a novel procedure to completely remove follicle cells from oocytes. Intact follicles, but not oocytes completely stripped of follicle cells, hyperpolarized in response to FSH, NECA, dibutyryl cAMP, microinjected cAMP, and forskolin, but not to dideoxyforskolin (which does not activate adenylyl cyclase). Injection of the catalytic subunit of cAMP-dependent protein kinase (which is too large to traverse gap junctions) into oocytes of intact follicles failed to activate a K+ current. These data suggest that FSH and adenosine hyperpolarize follicles by stimulating adenylyl cyclase and that cAMP-dependent protein kinase must be activated on both sides of follicle cell-oocyte gap junctions to elicit a hyperpolarizing K+ current.

Xenopus oocyte K+ current. II. Adenylyl cyclase-linked receptors on follicle cells

1990 ◽  
Vol 259 (5) ◽  
pp. C784-C791 ◽  
Author(s):  
L. J. Greenfield ◽  
J. T. Hackett ◽  
J. Linden
Keyword(s):  
Gap Junctions ◽  
Adenylyl Cyclase ◽  
Follicle Stimulating Hormone ◽  
Phosphodiesterase Inhibitor ◽  
Follicle Cells ◽  
Camp Accumulation ◽  
Collagenase Treatment ◽  
K Current ◽  
Small Follicle ◽  
K Currents

Xenopus ovarian follicles consist of single large oocytes surrounded by a layer of small follicle cells that are coupled to the oocyte by gap junctions. Hyperpolarizing K+ currents can be detected in the oocytes of follicles stimulated with adenosine, isoproterenol, follicle-stimulating hormone (FSH), or microinjected adenosine 3',5'-cyclic monophosphate (cAMP). We show that cAMP accumulation can be detected in follicles incubated with the adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA), isoproterenol, or FSH, but only if forskolin and a phosphodiesterase inhibitor are also added. Treatment of follicles with collagenase has been reported to reduce, but usually not to eliminate, cAMP-activated K+ currents. In this study we show that collagenase treatment alone does not completely remove follicle cells or receptor-mediated cAMP accumulation measured in follicles. cAMP accumulation and cAMP-dependent K+ currents are both eliminated when the follicle cells are completely removed by a technique involving treatment of follicles with collagenase and hypertonic saline. Oocytes completely stripped of follicle cells fail to accumulate cAMP in response to receptor agonists and forskolin. Isolated follicle cells derived from single follicles (but without the oocyte present) accumulate cAMP in response to these drugs to an extent equivalent to the response seen in single intact follicles. Adenylyl cyclase-linked receptors of Xenopus follicles thus appear to be located exclusively on follicle cells. The data suggest that cAMP-dependent K+ currents, although measured in oocytes, may be generated in follicle cells which communicate with oocytes. Another possibility is that a high resting K+ conductance in follicle cells is communicated to oocytes via cAMP-sensitive gap junctions.

Ultrastructural characteristics of the follicle cell-oocyte interface in the oogenesis of Ceratophrys cranwelli

Zygote ◽  
2002 ◽  
Vol 10 (2) ◽  
pp. 163-173 ◽  
Author(s):  
Evelina I. Villecco ◽  
Susana B. Genta ◽  
Alicia N. Sánchez Riera ◽  
Sara S. Sánchez
Keyword(s):  
Plasma Membrane ◽  
Granular Material ◽  
Gap Junctions ◽  
Close Contact ◽  
Follicle Cell ◽  
Follicle Cells ◽  
Apical Surface ◽  
Coated Pits ◽  
Compact Zone ◽  
Vitelline Envelope

In this work we carried out an ultrastructural analysis of the cell interface between oocyte and follicle cells during the oogenesis of the amphibian Ceratophrys cranwelli, which revealed a complex cell-cell interaction. In the early previtellogenic follicles, the plasma membrane of the follicle cells lies in close contact with the plasma membrane of the oocyte, with no interface between them. In the mid-previtellogenic follicles the follicle cells became more active and their cytoplasm has vesicles containing granular material. Their apical surface projects cytoplasmic processes (macrovilli) that contact the oocyte, forming gap junctions. The oocyte surface begins to develop microvilli. At the interface both processes delimit lacunae containing granular material. The oocyte surface has endocytic vesicles that incorporate this material, forming cortical vesicles that are peripherally arranged. In the late previtellogenic follicle the interface contains fibrillar material from which the vitelline envelope will originate. During the vitellogenic period, there is an increase in the number and length of the micro- and macrovilli, which become regularly arranged inside fibrillar tunnels. At this time the oocyte surface exhibits deep crypts where the macrovilli enter, thus increasing the follicle cell-oocyte junctions. In addition, the oocyte displays coated pits and vesicles evidencing an intense endocytic activity. At the interface of the fully grown oocyte the fibrillar network of the vitelline envelope can be seen. The compact zone contains a fibrillar electron-dense material that fills the spaces previously occupied by the now-retracted microvilli. The macrovilli are still in contact with the surface of the oocyte, forming gap junctions.

Regulation of gap junctional conductance

1985 ◽  
Vol 248 (6) ◽  
pp. H753-H764 ◽  
Author(s):  
D. C. Spray ◽  
R. L. White ◽  
F. Mazet ◽  
M. V. Bennett
Keyword(s):  
Gap Junctions ◽  
Ventricular Myocytes ◽  
Cross Reactivity ◽  
Cardiac Cells ◽  
Rat Ventricular Myocytes ◽  
Gating Mechanisms ◽  
Conduction Disorders ◽  
Wide Range ◽  
Junctional Conductance ◽  
Gap Junctional

Gap junctional conductance is regulated by the number of channels between coupled cells (the balance between formation and loss of these channels) and by the fraction of these channels that are open (gating mechanisms). A variety of treatments are known to affect junction formation. Adenosine 3',5'-cyclic monophosphate (cAMP) is involved in some cases, and protein synthesis may be required but precursor molecules can also exist. Junction removal occurs both by dispersion of particles and by internalization of junctional membrane. Factors promoting removal are not well understood. A variety of gating mechanisms exist. Coupling may be controlled by changes in conductance of nonjunctional membranes. Several kinds of voltage dependence of junctional conductance are known, but rat ventricular junctions at least are electrically linear. Cytoplasmic acidification decreases conductance of most gap junctions. Sensitivity in rat ventricular myocytes allows modulation of coupling by moderate changes near normal internal pH. Increasing intracellular Ca also decreases junctional conductance, but in the better studied cases sensitivity is much lower to Ca than H. A few data support low sensitivity to Ca in cardiac cells, but quantitative studies are lacking. Higher alcohols such as octanol block junctional conductance in a wide range of tissues including rat ventricular myocytes. An antibody to liver gap junctions blocks junctions between rat ventricular myocytes. Cross reactivity indicates at least partial homology between many gap junctions. Although differences among gap junctions are known, a general physiology is being developed, which may have considerable relevance to normal cardiac function and also to conduction disorders of that tissue.

scholarly journals Direct Actions of Carbenoxolone on Synaptic Transmission and Neuronal Membrane Properties

2009 ◽  
Vol 102 (2) ◽  
pp. 974-978 ◽  
Author(s):  
Kenneth R. Tovar ◽  
Brady J. Maher ◽  
Gary L. Westbrook
Keyword(s):  
Action Potential ◽  
Synaptic Transmission ◽  
Gap Junctions ◽  
Hippocampal Neurons ◽  
Electrical Coupling ◽  
Network Activity ◽  
Membrane Properties ◽  
Neuronal Membrane ◽  
Postsynaptic Currents ◽  
Gap Junctional

The increased appreciation of electrical coupling between neurons has led to many studies examining the role of gap junctions in synaptic and network activity. Although the gap junctional blocker carbenoxolone (CBX) is effective in reducing electrical coupling, it may have other actions as well. To study the non–gap junctional effects of CBX on synaptic transmission, we recorded from mouse hippocampal neurons cultured on glial micro-islands. This recording configuration allowed us to stimulate and record excitatory postsynaptic currents (EPSCs) or inhibitory postsynaptic currents (IPSCs) in the same neuron or pairs of neurons. CBX irreversibly reduced evoked α-amino-3-hydroxy-5-methyl-4-isoxazole-proprionic acid (AMPA) receptor–mediated EPSCs. Consistent with a presynaptic site of action, CBX had no effect on glutamate-evoked whole cell currents and increased the paired-pulse ratio of AMPA and N-methyl-d-aspartate (NMDA) receptor–mediated EPSCs. CBX also reversibly reduced GABAA receptor–mediated IPSCs, increased the action potential width, and reduced the action potential firing rate. Our results indicate CBX broadly affects several neuronal membrane conductances independent of its effects on gap junctions. Thus effects of carbenoxolone on network activity cannot be interpreted as resulting from specific block of gap junctions.

Cumulus expansion initiates physical and developmental autonomy of the oocyte

Zygote ◽  
1996 ◽  
Vol 4 (04) ◽  
pp. 335-341 ◽  
Author(s):  
William J. Larsen ◽  
Lin Chen ◽  
Robert Powers ◽  
Hong Zhang ◽  
Paul T. Russell ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Germ Cell ◽  
Cell Population ◽  
Follicle Cell ◽  
Ovarian Cycle ◽  
Follicle Cells ◽  
Cumulus Expansion ◽  
Primary Oocyte ◽  
Female Germ Cell

As meiosis is initiated and the oogonium is transformed into a primary oocyte, the female germ cell becomes intimately invested by a single squamous layer of sex cord epithelium. As the follicle cell population expands during the initial stages of the ovarian cycle, oocyte and follicle cells become increasingly connected to one another by one of the most extensive populations of gap junctions documented in any epithelium (reviewed in Larsen & Wert, 1988).

Implication of gap junction coupling in amphibian vitellogenin uptake

Zygote ◽  
2007 ◽  
Vol 15 (2) ◽  
pp. 149-157 ◽  
Author(s):  
M.E. Mónaco ◽  
E.I. Villecco ◽  
S.S. Sánchez
Keyword(s):  
Gap Junctions ◽  
Connexin 43 ◽  
Physiological Role ◽  
Follicle Cell ◽  
Pcr Analysis ◽  
Dye Transfer ◽  
Gap Junctional Communication ◽  
Junctional Communication ◽  
Endocytic Activity ◽  
Gap Junctional

SummaryThe aim of the present study was to investigate the physiological role and the expression pattern of heterologous gap junctions during Xenopus laevis vitellogenesis. Dye transfer experiments showed that there are functional gap junctions at the oocyte/follicle cell interface during the vitellogenic process and that octanol uncouples this intercellular communication. The incubation of vitellogenic oocytes in the presence of biotinylated bovine serum albumin (b-BSA) or fluorescein dextran (FDX), showed that oocytes develop stratum of newly formed yolk platelets. In octanol-treated follicles no sign of nascent yolk sphere formation was observed. Thus, experiments in which gap junctions were downregulated with octanol showed that coupled gap junctions are required for endocytic activity. RT-PCR analysis showed that the expression of connexin 43 (Cx43) was first evident at stage II of oogenesis and increased during the subsequent vitellogenic stages (III, IV and V), which would indicate that this Cx is related to the process that regulates yolk uptake. No expression changes were detected for Cx31 and Cx38 during vitellogenesis. Based on our results, we propose that direct gap junctional communication is a requirement for endocytic activity, as without the appropriate signal from surrounding epithelial cells X. laevis oocytes were unable to endocytose VTG.

scholarly journals Gap Junctions Regulate Extracellular Signal-regulated Kinase Signaling to Affect Gene Transcription

2005 ◽  
Vol 16 (1) ◽  
pp. 64-72 ◽  
Author(s):  
Joseph P. Stains ◽  
Roberto Civitelli
Keyword(s):  
Protein Kinase ◽  
Gap Junctions ◽  
Gap Junction ◽  
Gene Transcription ◽  
Electrical Coupling ◽  
Mitogen Activated Protein Kinase ◽  
Gap Junctional Communication ◽  
Junctional Communication ◽  
Extracellular Signal ◽  
Gap Junctional

Osteoblasts are highly coupled by gap junctions formed by connexin43. Overexpression of connexin45 in osteoblasts results in decreased chemical and electrical coupling and reduces gene transcription from connexin response elements (CxREs) in the osteocalcin and collagen Iα1 promoters. Here, we demonstrate that transcription from the gap junction-dependent osteocalcin CxRE is regulated by extracellular signal-regulated protein kinase (ERK) and phosphatidylinositol 3-kinase (PI3K) cascades. Overexpression of a constitutively active mitogen-activated protein kinase kinase (MEK), Raf, or Ras can increase transcription more than twofold of the CxRE, whereas inhibition of MEK or PI3K can decrease transcription threefold from the osteocalcin CxRE. Importantly, disruption of gap junctional communication by overexpression of connexin45 or treatment with pharmacological inhibitors of gap junctions results in reduced Raf, ERK, and Akt activation. The consequence of attenuated gap junction-dependent signal cascade activation is a decrease in Sp1 phosphorylation by ERK, resulting in decreased Sp1 recruitment to the CxRE and inhibited gene transcription. These data establish that ERK/PI3K signaling is required for the optimal elaboration of transcription from the osteocalcin CxRE, and that disruption of gap junctional communication attenuates the ability of cells to respond to an extracellular cue, presumably by limiting the propagation of second messengers among adjacent cells by connexin43-gap junctions.

scholarly journals Dopamine maintains network synchrony via direct modulation of gap junctions in the crustacean cardiac ganglion

2018 ◽  
Author(s):  
Brian J Lane ◽  
Daniel R Kick ◽  
David K Wilson ◽  
Satish S Nair ◽  
David J Schulz
Keyword(s):  
Motor Neurons ◽  
Channel Blocker ◽  
Electrical Coupling ◽  
Membrane Conductance ◽  
Large Cell ◽  
Protective Role ◽  
Cardiac Ganglion ◽  
Junctional Conductance ◽  
Network Synchrony ◽  
Gap Junctional

AbstractAbstract The Large Cell (LC) motor neurons of the crab (C. borealis) cardiac ganglion have variable membrane conductance magnitudes even within the same individual, yet produce identical synchronized activity in the intact network. In our previous study (Lane et al., 2016) we blocked a subset of K+ conductances across LCs, resulting in loss of synchronous activity. In this study, we hypothesized that this same variability of conductances could make LCs vulnerable to desynchronization during neuromodulation. We exposed the LCs to serotonin (5HT) and dopamine (DA) while recording simultaneously from multiple LCs. Both amines had distinct excitatory effects on LC output, but only 5HT caused desynchronized output. We further determined that DA rapidly increased gap junctional conductance. Co-application of both amines induced 5HT-like output, but waveforms remained synchronized. Furthermore, DA prevented desynchronization induced by the K+ channel blocker tetraethylammonium (TEA), suggesting that dopaminergic modulation of electrical coupling plays a protective role in maintaining network synchrony.

scholarly journals Substituted benzyl acetates: a new class of compounds that reduce gap junctional conductance by cytoplasmic acidification.

1984 ◽  
Vol 99 (1) ◽  
pp. 174-179 ◽  
Author(s):  
D C Spray ◽  
J Nerbonne ◽  
A Campos de Carvalho ◽  
A L Harris ◽  
M V Bennett
Keyword(s):  
Side Effects ◽  
Gap Junctions ◽  
Normal Tissue ◽  
Benzyl Acetate ◽  
Cytoplasmic Ph ◽  
Relative Lack ◽  
New Class ◽  
Junctional Conductance ◽  
Cytoplasmic Acidification ◽  
Gap Junctional

Conductance of gap junctions in many preparations has been shown to be sensitive to cytoplasmic pH, decreasing as pH decreases below 7.5 in fish and amphibian embryos and below 7.1 in crayfish septate axon. We have found a new class of compounds, benzyl acetate derivatives, that reversibly decrease junctional conductance, gj, when applied in low concentration (approximately 1 mM). Simultaneous intracellular pH (pHi) measurements show that the ester effects are attributable to reduction in pHi. The sensitivity of gj to these compounds and the relative lack of side effects make these agents attractive for studies of the role played by gap junctions in normal tissue function. In addition, the finding of cytoplasmic acidification in response to cell exposure to esters suggests caution in interpretation of results obtained using esterified compounds for intracellular loading.

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