Do Glial Gap Junctions Play a Role in Extracellular Ion Homeostasis?

Ransom, Bruce R.

doi:10.1007/978-3-662-21935-5_9

Cited by 21 publications

(24 citation statements)

References 81 publications

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“…Although gap junctions have been assumed necessary for extracellular K ϩ homeostasis by abetting spatial buffering, this has never been tested conclusively (Ransom, 1996). It should be added that gap junctions might also benefit extracellular K ϩ homeostasis attributable to net K ϩ uptake by stabilizing intracellular ion concentrations (Rose and Ransom, 1997).…”

Section: Discussionmentioning

confidence: 99%

“…4, 5). It is conceivable that astrocytic gap junctions help buffer K ϩ from stratum pyramidale by facilitating net uptake (proposed by Newman, 1995;Ransom, 1996) through spatial buffering in stratum lacunosum moleculare (Fig. 6 B) or by promoting spatial buffering in stratum radiatum in parallel to the neuronal cell layer (as discussed above).…”

Section: Astrocytic Kmentioning

confidence: 91%

“…؉ buffering Many groups have produced evidence in favor of net uptake of K ϩ or spatial buffering, which could coexist and vary in different brain regions (Ransom, 1996;Walz, 2000b;Kofuji and Newman, 2004 (Fig. 5).…”

Section: Astrocytic Kmentioning

confidence: 99%

“…2 E, F, 6B), single cells could be well suited to move K ϩ radially, without the participation of gap junctions, especially if part of the K ϩ is released from apical dendrites, at some distance from stratum pyramidale. In addition, partial overlap of elongated astrocytic processes might facilitate release of K ϩ from one astrocytic pole and uptake at the next, via K ϩ channels, a mechanism coined as "indirect coupling" (Newman, 1995;Ransom, 1996). In stratum lacunosum moleculare, on the contrary, relocation of K ϩ in radial direction was impaired in the absence of astrocytic gap junctions, demonstrating that junctional coupling can, indeed, contribute to spatial buffering.…”

Section: Astrocytic Kmentioning

confidence: 99%

“…Because of electrotonic propagation of the K ϩ -induced depolarization, a driving force for K ϩ efflux results at sites in which local depolarization exceeds the K ϩ equilibrium potential. It has been argued that a single elongated astrocyte might redistribute K ϩ from sites of maximal accumulation to sites of lower [K ϩ ] o (Ransom, 1996). Indeed, the seminal work of Newman (Newman et al, 1984;Newman, 1993) has demonstrated that the expression pattern of inwardly rectifying K ϩ channels along the longitudinal axis of retinal Müller cells enables uptake and redistribution of extracellular K ϩ , a process called K ϩ siphoning.…”

Section: Introductionmentioning

confidence: 99%

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The Impact of Astrocytic Gap Junctional Coupling on Potassium Buffering in the Hippocampus

Wallraff¹,

Köhling²,

Heinemann³

et al. 2006

J. Neurosci.

519

570

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Astrocytic gap junctions have been suggested to contribute to spatial buffering of potassium in the brain. Direct evidence has been difficult to gather because of the lack of astrocyte-specific gap junction blockers. We obtained mice with coupling-deficient astrocytes by crossing conditional connexin43-deficient mice with connexin30 Ϫ/Ϫ mice. Similar to wild-type astrocytes, genetically uncoupled hippocampal astrocytes displayed negative resting membrane potentials, time-and voltage-independent whole-cell currents, and typical astrocyte morphologies. Astrocyte densities were also unchanged. Using potassium-selective microelectrodes, we assessed changes in potassium buffering in hippocampal slices of mice with coupling-deficient astrocytes. We demonstrate that astrocytic gap junctions accelerate potassium clearance, limit potassium accumulation during synchronized neuronal firing, and aid in radial potassium relocation in the stratum lacunosum moleculare. Furthermore, slices of mice with coupling-deficient astrocytes displayed a reduced threshold for the generation of epileptiform events. However, it was evident that radial relocation of potassium in the stratum radiatum was not dependent on gap junctional coupling. We suggest that the perpendicular array of individual astrocytes in the stratum radiatum makes these cells ideally suited for spatial buffering of potassium released by pyramidal cells, independent of gap junctions. In general, a surprisingly large capacity for K ϩ clearance was conserved in mice with coupling-deficient astrocytes, indicating that gap junctiondependent processes only partially account for K ϩ buffering in the hippocampus.

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Section: Discussionmentioning

confidence: 99%

Section: Astrocytic Kmentioning

confidence: 91%

Section: Astrocytic Kmentioning

confidence: 99%

Section: Astrocytic Kmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The Impact of Astrocytic Gap Junctional Coupling on Potassium Buffering in the Hippocampus

Wallraff¹,

Köhling²,

Heinemann³

et al. 2006

J. Neurosci.

519

570

View full text Add to dashboard Cite

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Gap junctions equalize intracellular Na+ concentration in astrocytes

Rose

Ransom

1997

Glia

Self Cite

126

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Visualization and functional blocking of gap junction hemichannels (connexons) with antibodies against external loop domains in astrocytes

Höfer

Dermietzel

1998

Glia

131

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Astrocytes constitute a metabolically and electrically coupled syncytium which is essential for the regulation of ionic homeostasis of the interstitial brain fluid and for coordinating responses to neuronal activities. The structural avenues that couple individual astrocytes are provided by gap junctions which consist of transmembraneous channels that bridge the extracellular space. Each gap junction channel is composed of two hemichannels (connexons) that dock to each other via their extracellular loops. Here we report on the characterization of external loop antibodies that visualize hemichannels in specific plasma membranes of vital astrocytes. Hemichannels were found to be concentrated on cytoplasmic processes and filopodia of subconfluent cells. Specificity of hemichannel‐binding was evaluated by blockage of Lucifer Yellow (LY) dye‐transfer and Ca2+ transmission, as well as LY uptake under calcium‐deficient conditions. Our data indicate that hemichannels are accessible from the extracytoplasmic side either for direct visualization or functional manipulation. The availability of such a probe will allow in vivo experiments which require selective and/or temporal blocking of gap junctions in animal models. GLIA 24:141–154, 1998. © 1998 Wiley‐Liss, Inc.

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Do Glial Gap Junctions Play a Role in Extracellular Ion Homeostasis?

Cited by 21 publications

References 81 publications

The Impact of Astrocytic Gap Junctional Coupling on Potassium Buffering in the Hippocampus

The Impact of Astrocytic Gap Junctional Coupling on Potassium Buffering in the Hippocampus

Gap junctions equalize intracellular Na+ concentration in astrocytes

Visualization and functional blocking of gap junction hemichannels (connexons) with antibodies against external loop domains in astrocytes

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