scholarly journals Gap junction dynamics: reversible effects of divalent cations.

1980 ◽  
Vol 87 (3) ◽  
pp. 708-718 ◽  
Author(s):  
C Peracchia ◽  
L L Peracchia
Keyword(s):  
Gap Junction ◽  
Divalent Cations ◽  
Ionophore A23187 ◽  
Channel Narrowing ◽  
Lens Fibers ◽  
Electrical Uncoupling ◽  
Cytoplasmic Surface ◽  
Particle Packings ◽  
Cytoskeletal Elements ◽  
Junction Structure

Reversible changes in gap junction structure similar to those previously seen to parallel electrical uncoupling (9, 33, 34) are produced by treating with Ca++ or Mg++ gap junctions isolated in EDTA from calf lens fibers. The changes, characterized primarily by a switch from disordered to crystalline particle packings, occur at a [Ca++] of 5 x 10(-7) M or higher and a [Mg++] of 1 x 10(-3) M or higher and can be reversed by exposing the junctions to Ca++- and Mg++-free EGTA solutions. Similar changes are obtained in junctions of rat stomach epithelia incubated at 37 degrees C in well-oxygenated Tyrode's solutions containing a Ca++ ionophore (A23187). Deep etching experiments on isolated lens junctions show that the true cytoplasmic surface of the junctions (PS face) is mostly bare, suggesting that the particles may not be connected to cytoskeletal elements. A hypothesis is proposed suggesting a mechanism of particle aggregation and channel narrowing based on neutralization of negative charges by divalent cations or H+.

scholarly journals Gap junction dynamics: reversible effects of hydrogen ions.

1980 ◽  
Vol 87 (3) ◽  
pp. 719-727 ◽  
Author(s):  
C Peracchia ◽  
L L Peracchia
Keyword(s):  
Gap Junctions ◽  
Divalent Cations ◽  
Structural Characteristics ◽  
Freeze Fracture ◽  
Low Ph ◽  
Hydrogen Ions ◽  
Intact Cells ◽  
Lens Fibers ◽  
Fracture Appearance ◽  
Particle Packings

Reversible crystallization of intramembrane particle packings is induced in gap junctions isolated from calf lens fibers by exposure to 3 x 10(-7) M or higher [H+] (pH 6.5 or lower). The changes from disordered to crystalline particle packings induced by low pH are similar to those produced in junctions of intact cells by uncoupling treatments, indicating that H+, like divalent cations, could be an uncoupling agent. The freeze-fracture appearance of both control and low pH-treated gap junctions is not altered by glutaraldehyde fixation and cryoprotective treatment, as suggested by experiments in which gap junctions of both intact cells and isolated fractions are freeze-fractured after rapid freezing to liquid N2 temperature according to Heuser et al. (13). In junctions exposed to low pH, the particles most often form orthogonal and rhombic arrays, frequently fused with each other. A number of structural characteristics of these arrays suggest that the particles of lens fiber gap junctions may be shaped as tetrameres.

scholarly journals Cardiac gap junction configuration after an uncoupling treatment as a function of time.

1979 ◽  
Vol 82 (1) ◽  
pp. 66-75 ◽  
Author(s):  
K M Baldwin
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Freeze Fracture ◽  
Homogeneous Structure ◽  
Electrical Uncoupling ◽  
Gap Junctional ◽  
Injury Control ◽  
Junction Structure ◽  
Rabbit Atrium

Rabbit ventricle either was fixed in glutaraldehyde without injury (control) or was injured before fixation, presumably causing electrical uncoupling of the gap junctions. All tissue was then processed for freeze-fracture. Replicas of control gap junctions exhibited irregular packing of the P-face particles and E-face pits. Average center-to-center spacing of the particles was 10.5 nm. Tissue fixed 1-5 min after injury showed clumping of gap junctional particles and pits. Within the clumps, the particles and pits were hexagonally packed and the center-to-center spacing of the particles averaged 9.5 nm. In tissue fixed 15-30 min after injury, the clumps of gap junctional particles had coalesced into a homogeneous structure in most junctions. The packing of the particles and pits was hexagonal and the spacing of the particles averaged 9.5 nm. A few pieces of rabbit atrium were frozen without prior fixation or cryoprotection to try to assess the effect of glutarldehyde fixation on gap junction structure. In this tissue the gap junctional particles were irregularly packed and their spacing averaged 10.0 nm.

scholarly journals Zinc Modulation of Hemi-Gap-Junction Channel Currents in Retinal Horizontal Cells

2009 ◽  
Vol 101 (4) ◽  
pp. 1774-1780 ◽  
Author(s):  
Ziyi Sun ◽  
Dao-Qi Zhang ◽  
Douglas G. McMahon
Keyword(s):  
Gap Junction ◽  
Inhibitory Action ◽  
Divalent Cations ◽  
Horizontal Cells ◽  
Visual Signals ◽  
Histidine Residues ◽  
Gap Junction Channel ◽  
And Function ◽  
Channel Currents

Hemi-gap-junction (HGJ) channels of retinal horizontal cells (HCs) function as transmembrane ion channels that are modulated by voltage and calcium. As an endogenous retinal neuromodulator, zinc, which is coreleased with glutamate at photoreceptor synapses, plays an important role in shaping visual signals by acting on postsynaptic HCs in vivo. To understand more fully the regulation and function of HC HGJ channels, we examined the effect of Zn2+ on HGJ channel currents in bass retinal HCs. Hemichannel currents elicited by depolarization in Ca2+-free medium and in 1 mM Ca2+ medium were significantly inhibited by extracellular Zn2+. The inhibition by Zn2+ of hemichannel currents was dose dependent with a half-maximum inhibitory concentration of 37 μM. Compared with other divalent cations, Zn2+ exhibited higher inhibitory potency, with the order being Zn2+ > Cd2+ ≈ Co2+ > Ca2+ > Ba2+ > Mg2+. Zn2+ and Ca2+ were found to modulate HGJ channels independently in additivity experiments. Modification of histidine residues with N-bromosuccinimide suppressed the inhibitory action of Zn2+, whereas modification of cysteine residues had no significant effect on Zn2+ inhibition. Taken together, these results suggest that zinc acts on HGJ channels in a calcium-independent way and that histidine residues on the extracellular domain of HGJ channels mediate the inhibitory action of zinc.

Electrical properties of the gap junctional membrane studied in rat liver cell pairs

1988 ◽  
Vol 254 (2) ◽  
pp. C226-C234 ◽  
Author(s):  
E. C. Reverdin ◽  
R. Weingart
Keyword(s):  
Electrical Properties ◽  
Gap Junction ◽  
Rat Liver ◽  
Time Range ◽  
Voltage Gradient ◽  
Voltage Range ◽  
Cell Pair ◽  
Adult Rat ◽  
Electrical Uncoupling ◽  
Gap Junctional

Cell pairs isolated from adult rat liver were used to study the electrical properties of gap junctions. Each cell of a cell pair was connected to a suction pipette so as to enable whole cell tight-seal recording. A double voltage-clamp approach was adopted to control the voltage gradient across the gap junction and measure the transjunctional current. The current-voltage relationship of the gap junctional membrane was linear over the voltage range tested (+/- 50 m V). Under control conditions, the resistance of the gap junction, rj, was 15 M omega (n = 27; range, 4.6 to 45.8 M omega), corresponding to a conductance gj of 67 nS. rj was insensitive to the nonjunctional membrane potential, Vm (voltage range,-90 m V to + 40 m V). There was no indication of a time-dependent gating of rj (time range, 20 ms to 10 s). Dialysis with 1 mM CaCl2 produced irreversible electrical uncoupling without affecting the linearity of the relationship Vj/Ij.

scholarly journals Isoform-specific phosphorylation-dependent regulation of connexin hemichannels

2015 ◽  
Vol 114 (5) ◽  
pp. 3014-3022 ◽  
Author(s):  
Jette Skov Alstrøm ◽  
Daniel Bloch Hansen ◽  
Morten Schak Nielsen ◽  
Nanna MacAulay
Keyword(s):  
Gap Junction ◽  
Fluorescent Dyes ◽  
Divalent Cations ◽  
Phosphorylation Site ◽  
Xenopus Laevis Oocytes ◽  
Transmembrane Flux ◽  
Specific Permeability ◽  
Specific Regulation ◽  
Pkc Activation ◽  
Connexin Hemichannels

Connexins form gap junction channels made up of two connexons (hemichannels) from adjacent cells. Unopposed hemichannels may open toward the extracellular space upon stimulation by, e.g., removal of divalent cations from the extracellular solution and allow isoform-specific transmembrane flux of fluorescent dyes and physiologically relevant molecules, such as ATP and ions. Connexin (Cx)43 and Cx30 are the major astrocytic connexins. Protein kinase C (PKC) regulates Cx43 in its cell-cell gap junction configuration and may also act to keep Cx43 hemichannels closed. In contrast, the regulation of Cx30 hemichannels by PKC is unexplored. To determine phosphorylation-dependent regulation of Cx30 and Cx43 hemichannels, these were heterologously expressed in Xenopus laevis oocytes and opened with divalent cation-free solution. Inhibition of PKC activity did not affect hemichannel opening of either connexin. PKC activation had no effect on Cx43-mediated hemichannel activity, whereas both dye uptake and current through Cx30 hemichannels were reduced. We detected no PKC-induced connexin internalization from the plasma membrane, indicating that PKC reduced Cx30 hemichannel activity by channel closure. In an attempt to resolve the PKC phosphorylation site(s) on Cx30, alanine mutations of putative cytoplasmic PKC consensus sites were created to prevent phosphorylation (T5A, T8A, T102A, S222A, S225A, S239A, and S258A). These Cx30 mutants responded to PKC activation, suggesting that Cx30 hemichannels are not regulated by phosphorylation of a single site. In conclusion, Cx30, but not Cx43, hemichannels close upon PKC activation, illustrating that connexin hemichannels display not only isoform-specific permeability profiles but also isoform-specific regulation by PKC.

Sign in / Sign up

Export Citation Format

Share Document