scholarly journals Optical measurement of cell-to-cell coupling in intact heart using subthreshold electrical stimulation

2001 ◽  
Vol 281 (2) ◽  
pp. H533-H542 ◽  
Author(s):  
Fadi G. Akar ◽  
Bradley J. Roth ◽  
David S. Rosenbaum
Keyword(s):  
Fiber Orientation ◽  
Optical Measurement ◽  
Critical Role ◽  
Electrical Coupling ◽  
Membrane Properties ◽  
Cell Coupling ◽  
Close Proximity ◽  
Junctional Conductance ◽  
Gap Junctional ◽  
Intact Heart

Electrical coupling between myocytes plays a critical role in propagation, repolarization, and arrhythmias. On the basis of predictions from cable theory, we hypothesized that the cardiac space constant (λ) measured from the decay of subthreshold transmembrane potential (ST- V m) in space would provide an index of regional cell-to-cell coupling in the intact heart. With the use of voltage-sensitive dyes, the distribution of ST- V m was measured from hundreds of sites in close proximity to the site of subthreshold stimulation. λ was calculated from the exponential decay of ST- V min space. Consistent with known directional differences in axial resistance, the spatial distribution of ST- V mwas strongly dependent on fiber orientation, because λ was significantly ( P < 0.001) longer along (1.5 ± 0.1 mm) compared with across (0.8 ± 0.1 mm) fibers. There was a close linear relationship ( P < 0.001) between conduction velocity (CV) and λ along all fiber angles tested. Reducing gap junctional conductance by heptanol reversibly decreased CV and λ in parallel by ∼50%. In contrast, sodium channel blockade by flecainide slowed CV by 40% but had no effect on λ, reaffirming that λ was an index of passive but not active membrane properties. These data establish the feasibility of measuring λ as an index of cell-to-cell coupling in the intact heart, and indicate strong dependency of λ on fiber orientation and pharmacological alterations of gap junction conductance.

Gap-junctional properties of electrically coupled skate horizontal cells in culture

1993 ◽  
Vol 10 (2) ◽  
pp. 287-295 ◽  
Author(s):  
Haohua Qian ◽  
Robert Paul Malchow ◽  
Harris Ripps
Keyword(s):  
Receptive Field ◽  
Lucifer Yellow ◽  
Horizontal Cell ◽  
Electrical Coupling ◽  
Cell Voltage ◽  
Horizontal Cells ◽  
Electrical Synapse ◽  
Cell Coupling ◽  
Junctional Conductance ◽  
Gap Junctional

AbstractWhole-cell voltage-clamp recordings were used to examine the unusual pharmacological properties of the electrical coupling between rod-driven horizontal cells in skate retina as revealed previously by receptive-field measurements (Qian & Ripps, 1992). The junctional resistance was measured in electrically coupled cell pairs that had been enzymatically isolated and maintained in culture; the typical value was about 19.92 MΩ(n = 45), more than an order of magnitude lower than the nonjunctional membrane resistance. These data and the intercellular spread of the fluorescent dye Lucifer Yellow provide a good indication that skate horizontal cells are well coupled. The junctional conductance between cells was not modulated by the neurotransmitters dopamine (200 μM) or GABA (1 mM), nor was it affected by the membrane-permeable analogues of cAMP or cGMP, or the adenylate cyclase activator, forskolin. Although resistant to agents that have been reported to alter horizontal-cell coupling in cone-driven horizontal cells, the junctional conductance between paired horizontal cells of skate was greatly reduced by the application of 20 mM acetate, which is known to effectively reduce intracellular pH. Together with the results obtained in situ on the receptive-field properties of skate horizontal cells, these findings indicate that the gap-junctional properties of rod-driven horizontal cells of the skate are fundamentally different from those of cone-driven horizontal cells in other species. This raises the possibility that there is more than one class of electrical synapse on vertebrate horizontal cells.

Cell coupling in mouse pancreatic β-cells measured in intact islets of Langerhans

2008 ◽  
Vol 366 (1880) ◽  
pp. 3503-3523 ◽  
Author(s):  
Quan Zhang ◽  
Juris Galvanovskis ◽  
Fernando Abdulkader ◽  
Christopher J Partridge ◽  
Sven O Göpel ◽  
...  
Keyword(s):  
Voltage Clamp ◽  
Total Charge ◽  
Charge Movement ◽  
Cell Coupling ◽  
Β Cells ◽  
Patch Clamp Technique ◽  
Intact Mouse ◽  
Whole Cell ◽  
Junctional Conductance ◽  
Gap Junctional

The perforated whole-cell configuration of the patch-clamp technique was applied to functionally identified β-cells in intact mouse pancreatic islets to study the extent of cell coupling between adjacent β-cells. Using a combination of current- and voltage-clamp recordings, the total gap junctional conductance between β-cells in an islet was estimated to be 1.22 nS. The analysis of the current waveforms in a voltage-clamped cell (due to the firing of an action potential in a neighbouring cell) suggested that the gap junctional conductance between a pair of β-cells was 0.17 nS. Subthreshold voltage-clamp depolarization (to −55 mV) gave rise to a slow capacitive current indicative of coupling between β-cells, but not in non-β-cells, with a time constant of 13.5 ms and a total charge movement of 0.2 pC. Our data suggest that a superficial β-cell in an islet is in electrical contact with six to seven other β-cells. No evidence for dye coupling was obtained when cells were dialysed with Lucifer yellow even when electrical coupling was apparent. The correction of the measured resting conductance for the contribution of the gap junctional conductance indicated that the whole-cell K ATP channel conductance ( G K,ATP ) falls from approximately 2.5 nS in the absence of glucose to 0.1 nS at 15 mM glucose with an estimated IC 50 of approximately 4 mM. Theoretical considerations indicate that the coupling between β-cells within the islet is sufficient to allow propagation of [Ca 2+ ] i waves to spread with a speed of approximately 80 μm s −1 , similar to that observed experimentally in confocal [Ca 2+ ] i imaging.

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.

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

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Brian J Lane ◽  
Daniel R Kick ◽  
David K Wilson ◽  
Satish S Nair ◽  
David J Schulz
Keyword(s):  
Motor Neurons ◽  
Electrical Coupling ◽  
Membrane Conductance ◽  
Large Cell ◽  
Protective Role ◽  
K Channel ◽  
Cardiac Ganglion ◽  
Junctional Conductance ◽  
Network Synchrony ◽  
Gap Junctional

The Large Cell (LC) motor neurons of the crab cardiac ganglion have variable membrane conductance magnitudes even within the same individual, yet produce identical synchronized activity in the intact network. In a previous study we blocked a subset of K+ conductances across LCs, resulting in loss of synchronous activity (Lane et al., 2016). In this study, we hypothesized that this same variability of conductances makes 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.

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.

Electrical Coupling and Passive Membrane Properties of AII Amacrine Cells

2010 ◽  
Vol 103 (3) ◽  
pp. 1456-1466 ◽  
Author(s):  
Margaret Lin Veruki ◽  
Leif Oltedal ◽  
Espen Hartveit
Keyword(s):  
Amacrine Cell ◽  
Electrical Coupling ◽  
Amacrine Cells ◽  
Input Resistance ◽  
Membrane Resistance ◽  
Membrane Properties ◽  
Total Input ◽  
Junctional Conductance ◽  
Aii Amacrine Cells ◽  
Aii Amacrine

AII amacrine cells in the mammalian retina are connected via electrical synapses to on-cone bipolar cells and to other AII amacrine cells. To understand synaptic integration in these interneurons, we need information about the junctional conductance ( gj), the membrane resistance ( rm), the membrane capacitance ( Cm), and the cytoplasmic resistivity ( Ri). Due to the extensive electrical coupling, it is difficult to obtain estimates of rm, as well as the relative contribution of the junctional and nonjunctional conductances to the total input resistance of an AII amacrine cell. Here we used dual voltage-clamp recording of pairs of electrically coupled AII amacrine cells in an in vitro slice preparation from rat retina and applied meclofenamic acid (MFA) to block the electrical coupling and isolate single AII amacrines electrically. In the control condition, the input resistance ( Rin) was ∼620 MΩ and the apparent rm was ∼760 MΩ. After block of electrical coupling, determined by estimating gj in the dual recordings, Rin and rm were ∼4,400 MΩ, suggesting that the nongap junctional conductance of an AII amacrine cell is ∼16% of the total input conductance. Control experiments with nucleated patches from AII amacrine cells suggested that MFA had no effect on the nongap junctional membrane of these cells. From morphological reconstructions of AII amacrine cells filled with biocytin, we obtained a surface area of ∼900 μm2 which, with a standard value for Cm of 0.01 pF/μm2, corresponds to an average capacitance of ∼9 pF and a specific membrane resistance of ∼41 kΩ cm2. Together with information concerning synaptic connectivity, these data will be important for developing realistic compartmental models of the network of AII amacrine cells.

scholarly journals Novel Self-Healing Metallocopolymers with Pendent 4-Phenyl-2,2′:6′,2″-terpyridine Ligand: Kinetic Studies and Mechanical Properties

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1760
Author(s):  
Rose K. Baimuratova ◽  
Gulzhian I. Dzhardimalieva ◽  
Evgeniy V. Vaganov ◽  
Valentina A. Lesnichaya ◽  
Gulsara D. Kugabaeva ◽  
...  
Keyword(s):  
Critical Role ◽  
Specific Effect ◽  
Kinetic Studies ◽  
Radical Copolymerization ◽  
Self Healing ◽  
Free Radical Copolymerization ◽  
Polymer Hydrogels ◽  
Close Proximity ◽  
Metal Group ◽  
Metal Polymer

We report here our successful attempt to obtain self-healing supramolecular hydrogels with new metal-containing monomers (MCMs) with pendent 4-phenyl-2,2′:6′,2″-terpyridine metal complexes as reversible moieties by free radical copolymerization of MCMs with vinyl monomers, such as acrylic acid and acrylamide. The resulting metal-polymer hydrogels demonstrate a developed system of hydrogen, coordination and electron-complementary π–π stacking interactions, which play a critical role in achieving self-healing. Kinetic data show that the addition of a third metal-containing comonomer to the system decreases the initial polymerization rate, which is due to the specific effect of the metal group located in close proximity of the active center on the growth of radicals.

scholarly journals Embryological Remnants of the Thyroid Gland and their Significance in Thyroidectomy

2014 ◽  
Vol 6 (3) ◽  
pp. 110-112 ◽  
Author(s):  
R Fernando ◽  
Anuradha Rajapaksha ◽  
Narada Ranasinghe ◽  
Duminda Gunawardana
Keyword(s):  
Thyroid Gland ◽  
Current Knowledge ◽  
Critical Role ◽  
Close Proximity ◽  
Pyramidal Lobe

ABSTRACT Thyroid gland has three main embryological remnants: pyramidal lobe, tubercle of Zuckerkandl and thyrothymic remnants. They are commonly missed or misidentified during dissection. Each of these remnants plays a critical role in thyroidectomy as they help to identify the relevant anatomy and therefore help prevent accidental damage to other structures in close proximity during dissection. In this article, we describe the current knowledge of each of these remnants and their significance in thyroidectomy. Conclusion It is important that all these remnants are objectively looked for and removed during surgery in order to prevent recurrences. How to cite this article Fernando R, Rajapaksha A, Ranasinghe N, Gunawardana D. Embryological Remnants of the Thyroid Gland and their Significance in Thyroidectomy. World J Endoc Surg 2014;6(3):110-112.

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