Time Course of Ion Channel Development inXenopusMuscle Inducedin Vitroby Activin

Prokaryotic channels, such as Erwinia chrysanthemi ligand-gated ion channel (ELIC) and Gloeobacter violaceus ligand-gated ion channel, give key structural information for the pentameric ligand-gated ion channel family, which includes nicotinic acetylcholine receptors. ELIC, a cationic channel from E. chrysanthemi, is particularly suitable for single-channel recording because of its high conductance. Here, we report on the kinetic properties of ELIC channels expressed in human embryonic kidney 293 cells. Single-channel currents elicited by the full agonist propylamine (0.5–50 mM) in outside-out patches at −60 mV were analyzed by direct maximum likelihood fitting of kinetic schemes to the idealized data. Several mechanisms were tested, and their adequacy was judged by comparing the predictions of the best fit obtained with the observable features of the experimental data. These included open-/shut-time distributions and the time course of macroscopic propylamine-activated currents elicited by fast theta-tube applications (50–600 ms, 1–50 mM, −100 mV). Related eukaryotic channels, such as glycine and nicotinic receptors, when fully liganded open with high efficacy to a single open state, reached via a preopening intermediate. The simplest adequate description of their activation, the “Flip” model, assumes a concerted transition to a single intermediate state at high agonist concentration. In contrast, ELIC open-time distributions at saturating propylamine showed multiple components. Thus, more than one open state must be accessible to the fully liganded channel. The “Primed” model allows opening from multiple fully liganded intermediates. The best fits of this type of model showed that ELIC maximum open probability (99%) is reached when at least two and probably three molecules of agonist have bound to the channel. The overall efficacy with which the fully liganded channel opens was ∼102 (∼20 for α1β glycine channels). The microscopic affinity for the agonist increased as the channel activated, from 7 mM for the resting state to 0.15 mM for the partially activated intermediate state.

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The time-course of the response to the FMRFamide-related peptide PF4 in Ascaris suum muscle cells indicates direct gating of a chloride ion-channel

Parasitology ◽

10.1017/s0031182002001695 ◽

2002 ◽

Vol 124 (6) ◽

pp. 649-656 ◽

Cited By ~ 10

Author(s):

J. PURCELL ◽

A. P. ROBERTSON ◽

D. P. THOMPSON ◽

R. J. MARTIN

Keyword(s):

Ion Channel ◽

Time Course ◽

Ascaris Suum ◽

Chloride Ion ◽

Muscle Cells ◽

Ion Conductance ◽

Gaba A ◽

Electrode Current ◽

Related Peptide ◽

Free Living Nematode

We investigated the effects of PF4 on Ascaris suum somatic muscle cells using a 2 electrode current-clamp technique. PF4 is a FaRP (FMRFamide-related peptide), originally isolated from the free-living nematode Panagrellus redivivus. PF4 caused hyperpolarization and an increase in chloride ion conductance when it was applied to the muscle cells of the Ascaris body wall. The delay between the application of the peptide and the appearance of the response was measured and compared with that of gamma-amino butyric acid (GABA), a compound that directly gates ion channels, and with PF1, a FaRP that acts via an intracellular signal transduction mechanism. The PF4 and GABA delay times were not significantly different; they were 1·51±0·11 sec and 1·22±0·10 sec respectively. The delay following application of PF1, 3·75±0·51 sec, was significantly longer. The rapid response to PF4 is consistent with direct gating of a chloride ion channel, which has not been described elsewhere in the literature.

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Commentary: Slowing of the Time Course of Acidification Decreases the Acid-Sensing Ion Channel 1a Current Amplitude and Modulates Action Potential Firing in Neurons

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2021.714204 ◽

2021 ◽

Vol 15 ◽

Author(s):

Matthew William ◽

Victoria Cegielski ◽

Xiang-Ping Chu

Keyword(s):

Action Potential ◽

Ion Channel ◽

Time Course ◽

Current Amplitude ◽

Action Potential Firing ◽

Potential Firing

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Development of Gap Junctions in Hippocampal Astrocytes: Evidence That Whole Cell Electrophysiological Phenotype Is an Intrinsic Property of the Individual Cell

Journal of Neurophysiology ◽

10.1152/jn.00449.2006 ◽

2006 ◽

Vol 96 (3) ◽

pp. 1383-1392 ◽

Cited By ~ 53

Author(s):

Gary P. Schools ◽

Min Zhou ◽

Harold K. Kimelberg

Keyword(s):

Gap Junctions ◽

Ion Channel ◽

Gap Junction ◽

Time Course ◽

Expression Profiles ◽

Dye Coupling ◽

Cell Coupling ◽

Whole Cell ◽

Channel Expression ◽

Mature Astrocyte

Gap junction communication between astrocytes is prevalent and has been proposed to be involved in several astrocyte functions. One such proposal involves gap junctions in potassium spatial buffering. However, little is known about the developmental time course of gap junction coupling and how much the syncytium affects whole cell measurements of ion currents. Our previous work described three types of hippocampal astrocyte, each with a distinct electrophysiological profile when recorded in whole cell voltage-clamp mode. In the current study we correlated post–whole cell recording immunohistochemistry for GLAST and the spread of injected dye from the recorded cell with the measured electrophysiological phenotype to quantify cell coupling of astrocytes and the type of astrocyte coupled, in the rat hippocampus. We found that passive astrocytes, which predominate after 3 wk postnatally, have much lower membrane resistances ( Rm) and are more frequently dye coupled and to more cells, than outwardly and variably rectifying astrocytes that predominate in early postnatal development. Dye coupling in GLAST(+) cells was first detected in the first postnatal week and the degree of coupling peaked before the complete transition to the low Rm, passive electrophysiological type. Also, the degree of dye coupling did not correlate with the passive electrophysiological phenotype. Passive cells were also detected after pretreatment with a gap junction inhibitor. Further evidence that cell coupling does not contribute to the mature astrocyte electrophysiological phenotype came from recording of excised membrane patches, which predominantly corresponded to the ion channel expression profiles of their cells of origin. These findings imply that in the hippocampus, interastrocyte cell coupling likely contributes little to the overall whole cell current profile of diverse glia, and the electrophysiological passivity reflects the intrinsic ion channel expression of the mature astrocyte.

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Progesterone treatment abolishes exogenously expressed ionic currents in Xenopus oocytes

AJP Cell Physiology ◽

10.1152/ajpcell.2001.280.3.c677 ◽

2001 ◽

Vol 280 (3) ◽

pp. C677-C688 ◽

Cited By ~ 14

Author(s):

Anatoly D. Shcherbatko ◽

Christopher M. Davenport ◽

Joan C. Speh ◽

Simon R. Levinson ◽

Gail Mandel ◽

...

Keyword(s):

Membrane Proteins ◽

Ion Channel ◽

Time Course ◽

Xenopus Oocytes ◽

Surface Membrane ◽

Ionic Currents ◽

Germinal Vesicle Breakdown ◽

Α Subunit ◽

Progesterone Treatment ◽

Channel Inhibition

Fully grown oocytes of Xenopus laevis undergo resumption of the meiotic cycle when treated with the steroid hormone progesterone. Previous studies have shown that meiotic maturation results in profound downregulation of specific endogenous membrane proteins in oocytes. To determine whether the maturation impacts the functional properties of exogenously expressed membrane proteins, we used cut-open recordings from Xenopus oocytes expressing several types of Na+ and K+ channels. Treatment of oocytes with progesterone resulted in a downregulation of heterologously expressed Na+ and K+ channels without a change in the kinetics of the currents. The time course of progesterone-induced ion channel inhibition was concentration dependent. Complete elimination of Na+ currents temporally coincided with development of germinal vesicle breakdown, while elimination of K+currents was delayed by ∼2 h. Coexpression of human β1-subunit with rat skeletal muscle α-subunit in Xenopus oocytes did not prevent progesterone-induced downregulation of Na+ channels. Addition of 8-bromo-cAMP to oocytes or injection of heparin before progesterone treatment prevented the loss of expressed currents. Pharmacological studies suggest that the inhibitory effects of progesterone on expressed Na+ and K+ channels occur downstream of the activation of cdc2 kinase. The loss of channels is correlated with a reduction in Na+ channel immunofluorescence, pointing to a disappearance of the ion channel-forming proteins from the surface membrane.

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Astrocytes, as well as neurons, express a diversity of ion channels

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y92-266 ◽

1992 ◽

Vol 70 (S1) ◽

pp. S223-S238 ◽

Cited By ~ 42

Author(s):

H. Sontheimer

Keyword(s):

Ion Channels ◽

Ion Channel ◽

Brain Regions ◽

Regional Heterogeneity ◽

The Past ◽

Channel Expression ◽

Cell Processes ◽

Ion Channel Development ◽

The Brain

The electrophysiologist's view of brain astrocytes has changed markedly in recent years. In the past astrocytes were viewed as passive, K+ selective cells, but it is now evident that they are capable of expressing voltage- and ligand-activated channels previously thought to be restricted to neurons. The functional importance of most of these ion channels is not understood at present. However, from studies of astrocytes cultured from different species and brain regions, we learned that like their neuronal counterparts astrocytes are a heterogeneous group of brain cells showing similar heterogeneity in their ion-channel expression. Not only are subpopulations of astrocytes within areas of the brain equipped with specific sets of ion channels but, furthermore, regional heterogeneity is apparent. In addition, astrocyte ion channel expression is dynamic and changes during development. Some ion channels are only expressed postnatally, yet others appear to be expressed only during certain stages of development. Interestingly, the expression of some astrocyte channels, including Na+, Ca2+, and some K+ channels, appears to be controlled by neurons via mechanisms that are presently unknown. Some studies suggest roles for astrocyte channels in basic cell processes such as cell proliferation. Thus, although the role of some astrocyte channels remains unclear, our understanding of astrocyte physiology is starting to take shape and points towards roles of ion channels not involved in electrogenesis.Key words: astrocyte, ion channel, development, review, transmitter receptor.

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