scholarly journals Charge at the 46th residue of connexin 50 is crucial for the gap‐junctional unitary conductance and transjunctional voltage‐dependent gating

2014 ◽  
Vol 592 (23) ◽  
pp. 5187-5202 ◽  
Author(s):  
Xiaoling Tong ◽  
Hiroshi Aoyama ◽  
Tomitake Tsukihara ◽  
Donglin Bai
Keyword(s):  
Unitary Conductance ◽  
Voltage Dependent ◽  
Connexin 50 ◽  
Gap Junctional

Properties of gap junction channels formed of connexin 45 endogenously expressed in human hepatoma (SKHep1) cells

1995 ◽  
Vol 268 (2) ◽  
pp. C356-C365 ◽  
Author(s):  
A. P. Moreno ◽  
J. G. Laing ◽  
E. C. Beyer ◽  
D. C. Spray
Keyword(s):  
Gap Junction ◽  
Voltage Dependence ◽  
Hepatoma Cell ◽  
Hepatoma Cell Line ◽  
Voltage Sensitivity ◽  
Gap Junction Channels ◽  
Unitary Conductance ◽  
Junction Protein ◽  
Voltage Dependent ◽  
Gap Junctional

We have evaluated the voltage dependence and unitary conductance of gap junctional channels that were recorded in a clone isolated from the hepatoma cell line SKHep1. In this clonal population (designated SKHep1A), Northern blots, immunoprecipitation, and immunohistochemical staining demonstrated the expression of connexin (Cx) 45; no other gap junction protein was identified by these techniques, although weak hybridization with Cx40 was detected. Macroscopic junctional conductance (gj) in these cells was low, averaging 1.3 nS, and was steeply voltage dependent. Parameters of voltage sensitivity were as follows: voltage at which voltage-sensitive conductance is reduced by 50%, 13.4 mV; steepness of relation, 0.115 (corresponding to 2.7 gating charges), and voltage-insensitive fraction of residual to total conductance approximately 0.06. Unitary conductance (gamma j) of these junctional channels averaged 32 +/- 8 pS; although gamma j was independent of transjunctional voltage (Vj), at high Vj values (> 50 mV), smaller conductance values were also detected. Open probabilities of the 30-pS channels at various Vj values closely matched the predicted voltage-dependent component of macroscopic gj, the residual conductance at high Vj might be attributable to the smaller conductance events. The voltage dependence of human Cx45 gap junction channels is as steep as that seen for channels formed by Xenopus Cx38 and is much steeper than that previously reported for channels formed of the highly homologous chick Cx45 and for other mammalian connexins expressed either endogenously or exogenously.

scholarly journals Properties of a nonjunctional current expressed from a rat connexin46 cDNA in Xenopus oocytes.

1993 ◽  
Vol 102 (1) ◽  
pp. 59-74 ◽  
Author(s):  
L Ebihara ◽  
E Steiner
Keyword(s):  
Xenopus Oocytes ◽  
Inactivation Kinetics ◽  
Induced Current ◽  
Strongly Coupled ◽  
Deactivation Kinetics ◽  
Voltage Dependent ◽  
Junctional Protein ◽  
Gap Junctional ◽  
Kinetics Of ◽  
External Calcium

Connexin46 (cxn46) is a gap junctional protein that was cloned from a rat lens cDNA library. Expression of cxn46 in solitary Xenopus oocytes resulted in the development of a large time- and voltage-dependent current that was not observed in noninjected control oocytes or in oocytes injected with mRNA for cxn43 or cxn32. The cxn46-induced current activated at potentials positive to -20 mV. On repolarization to -40 mV, the current deactivated over a period of several seconds. Removal of external calcium caused a marked increase in the amplitude of the cxn46-induced current, shifted the steady-state activation curve to more negative potentials, and altered the kinetics of activation and deactivation. Increasing external calcium had the opposite effect. The ability of cxn46 to induce the formation of cell-to-cell channels was tested in the oocyte pair system. Oocyte pairs injected with cxn46 mRNA + antisense oligonucleotides for Xenopus cxn38 were strongly coupled. In contrast, oocyte pairs injected with antisense alone showed no coupling. The inactivation kinetics of the gap junctional channels resembled the deactivation kinetics of the cxn46-induced current in solitary oocytes.

scholarly journals A novel action of quinine and quinidine on the membrane conductance of neurons from the vertebrate retina.

1994 ◽  
Vol 104 (6) ◽  
pp. 1039-1055 ◽  
Author(s):  
R P Malchow ◽  
H Qian ◽  
H Ripps
Keyword(s):  
Lucifer Yellow ◽  
Reversal Potential ◽  
Outward Current ◽  
Membrane Conductance ◽  
Cobalt Acetate ◽  
Cinchona Alkaloids ◽  
Horizontal Cells ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Gap Junctional

The cinchona alkaloids quinine and quinidine have been shown to block a broad range of voltage-gated membrane conductances in a variety of excitable tissues. Using the whole-cell version of the patch clamp technique, we examined the effects of these compounds on voltage-dependent currents from horizontal cells dissociated enzymatically from the all-rod retina of the skate. We report here a novel and unexpected action of quinine and quinidine on isolated horizontal cells. In addition to blocking several of the voltage-activated currents of these cells, the introduction of the alkaloids evoked a large outward current when the cells were held at depolarized potentials. Using tail current analysis, the reversal potential of the outward current was close to O mV, and the current was markedly suppressed by extracellularly applied cobalt, acetate, and halothane. Depolarization in the presence of quinine also permitted entry into the cells of extracellularly applied Lucifer yellow (MW = 443 D), whereas a 3-kD fluorescein-dextran complex was excluded. These findings suggest that the large, apparently nonselective conductance induced by quinine and quinidine results from the opening of hemi-gap junctional channels.

Molecular mechanism underlying a Cx50-linked congenital cataract

1999 ◽  
Vol 276 (6) ◽  
pp. C1443-C1446 ◽  
Author(s):  
J. D. Pal ◽  
V. M. Berthoud ◽  
E. C. Beyer ◽  
D. Mackay ◽  
A. Shiels ◽  
...  
Keyword(s):  
Congenital Cataract ◽  
Xenopus Oocytes ◽  
Dominant Negative ◽  
Wild Type ◽  
Autosomal Dominant Fashion ◽  
Junctional Coupling ◽  
Type Coupling ◽  
Connexin 50 ◽  
Gap Junctional ◽  
Gap Junctional Coupling

Mutations in gap junctional channels have been linked to certain forms of inherited congenital cataract (D. Mackay, A. Ionides, V. Berry, A. Moore, S. Bhattacharya, and A. Shiels. Am. J. Hum. Genet. 60: 1474–1478, 1997; A. Shiels, D. Mackay, A. Ionides, V. Berry, A. Moore, and S. Bhattacharya. Am. J. Hum. Genet. 62: 526–532, 1998). We used the Xenopus oocyte pair system to investigate the functional properties of a missense mutation in the human connexin 50 gene (P88S) associated with zonular pulverulent cataract. The associated phenotype for the mutation is transmitted in an autosomal dominant fashion. Xenopus oocytes injected with wild-type connexin 50 cRNA developed gap junctional conductances of ∼5 μS 4–7 h after pairing. In contrast, the P88S mutant connexin failed to form functional gap junctional channels when paired homotypically. Moreover, the P88S mutant functioned in a dominant negative manner as an inhibitor of human connexin 50 gap junctional channels when coinjected with wild-type connexin 50 cRNA. Cells injected with 1:5 and 1:11 ratios of P88S mutant to wild-type cRNA exhibited gap junctional coupling of ∼8% and 39% of wild-type coupling, respectively. Based on these findings, we conclude that only one P88S mutant subunit is necessary per gap junctional channel to abolish channel function.

scholarly journals Anion and cation permeability of a chloride channel in rat hippocampal neurons.

1987 ◽  
Vol 90 (4) ◽  
pp. 453-478 ◽  
Author(s):  
F Franciolini ◽  
W Nonner
Keyword(s):  
Hippocampal Neurons ◽  
Anionic Site ◽  
Permeability Ratio ◽  
Unitary Conductance ◽  
Cation Permeability ◽  
Voltage Dependent ◽  
Salt Gradient ◽  
Activated Complex ◽  
Reversal Potentials ◽  
Patch Clamp Method

The ionic permeability of a voltage-dependent Cl channel of rat hippocampal neurons was studied with the patch-clamp method. The unitary conductance of this channel was approximately 30 pS in symmetrical 150 mM NaCl saline. Reversal potentials interpreted in terms of the Goldman-Hodgkin-Katz voltage equation indicate a Cl:Na permeability ratio of approximately 5:1 for conditions where there is a salt gradient. Many anions are permeant; permeability generally follows a lyotropic sequence. Permeant cations include Li, Na, K, and Cs. The unitary conductance does not saturate for NaCl concentrations up to 1 M. No Na current is observed when the anion Cl is replaced by the impermeant anion SO4. Unitary conductance depends on the cation species present. The channel is reversibly blocked by extracellular Zn or 9-anthracene carboxylic acid. Physiological concentrations of Ca or Mg do not affect the Na:Cl permeability ratio. The permeability properties of the channel are consistent with a permeation mechanism that involves an activated complex of an anionic site, an extrinsic cation, and an extrinsic anion.

On the electrical passivity of astrocyte potassium conductance

2021 ◽  
Author(s):  
Min Zhou ◽  
Yixing Du ◽  
Sydney Aten ◽  
David Terman
Keyword(s):  
Potassium Conductance ◽  
Membrane Conductance ◽  
Constant Field ◽  
Passive Behavior ◽  
Voltage Dependent ◽  
Junctional Coupling ◽  
Gap Junctional ◽  
Gap Junctional Coupling ◽  
Pore Domain ◽  
Inwardly Rectifying

Predominant expression of leak-type K+ channels provides astrocytes a high membrane permeability to K+ ions and a hyperpolarized membrane potential that are crucial for astrocyte function in brain homeostasis. In functionally mature astrocytes, the expression of leak K+ channels creates a unique membrane K+ conductance that lacks voltage-dependent rectification. Accordingly, the conductance is named ohmic or passive K+ conductance. Several inwardly rectifiers and two-pore domain K+ channels have been investigated for their contributions to passive conductance. Meanwhile, gap junctional coupling has been postulated to underlie the passive behavior of membrane conductance. It is now clear that the intrinsic properties of K+ channels and gap junctional coupling can each act alone or together to bring about a passive behavior of astrocyte conductance. Additionally, while the passive conductance can generally be viewed as a K+ conductance, the actual representation of this conductance is a combined expression of multiple known and unknown K+ channels, which has been further modified by the intricate morphology of individual astrocytes and syncytial gap junctional coupling. The expression of the inwardly rectifying K+ channels explains the inward-going component of passive conductance disobeying Goldman-Hodgkin-Kate (GHK) constant field outward rectification. However, the K+ channels encoding the outward-going passive currents remain to be determined in the future. Here, we review our current understanding of ion channels and biophysical mechanisms engaged in the passive astrocyte K+ conductance, propose new studies to resolve this long-standing puzzle in astrocyte physiology, and discuss the functional implication(s) of passive behavior of K+ conductance on astrocyte physiology.

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