Evidence for the co-localization of another connexin with connexin-43 at astrocytic gap junctions in rat brain

Nagy, J.I.; Ochalski, P.A.Y; Li, J; Hertzberg, Elliot L.

doi:10.1016/s0306-4522(96)00584-2

Cited by 93 publications

(71 citation statements)

References 35 publications

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“…At low magnification, conspicuous 20-nm gold particles revealed the presence of Cx43 in gap junctions of ependymal cells ( Fig. 2A), confirming previous immunocytochemical studies (25). Discrete (nonclumped) anti-Cx43 gold labels were present at 100-300 per m In double-labeled ependymocytes, anti-AQP4͞10-nm gold labels were restricted almost exclusively to the relatively rare square arrays (Fig.…”

Section: Resultssupporting

confidence: 87%

Direct immunogold labeling of aquaporin-4 in square arrays of astrocyte and ependymocyte plasma membranes in rat brain and spinal cord

Rash

Yasumura

Hudson

et al. 1998

Proc. Natl. Acad. Sci. U.S.A.

550

425

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Aquaporin (AQP) water channels are abundant in the brain and spinal cord, where AQP1 and AQP4 are believed to play major roles in water metabolism and osmoregulation. Immunocytochemical analysis of the brain recently revealed that AQP4 has a highly polarized distribution, with marked expression in astrocyte end-feet that surround capillaries and form the glia limitans; however, the structural organization of AQP4 has remained unknown. In freezefracture replicas, astrocyte end-feet contain abundant square arrays of intramembrane particles that parallel the distribution of AQP4. To determine whether astrocyte and ependymocyte square arrays contain AQP4, we employed immunogold labeling of SDS-washed freeze-fracture replicas and stereoscopic confirmation of tissue binding. Antibodies to AQP4 directly labeled Ϸ33% of square arrays in astrocyte and ependymocyte plasma membranes in rat brain and spinal cord. Overall, 84% of labels were present beneath square arrays; 11% were beneath particle clusters that resembled square arrays that had been altered during fixation or cleaving; and 5% were beneath the much larger areas of glial plasma membrane that were devoid of square arrays. Based on this evidence that AQP4 is concentrated in glial square arrays, freeze-fracture methods may now provide biophysical insights regarding neuropathological states in which abnormal f luid shifts are accompanied by alterations in the aggregation state or the molecular architecture of square arrays.

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Section: Resultssupporting

confidence: 87%

Direct immunogold labeling of aquaporin-4 in square arrays of astrocyte and ependymocyte plasma membranes in rat brain and spinal cord

Rash

Yasumura

Hudson

et al. 1998

Proc. Natl. Acad. Sci. U.S.A.

550

425

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“…Astrocytes express Cx43 and lower levels of Cx26, Cx30, Cx40, and Cx45 [90,91,34,116] (see Nagy et al [157]; Sfhl et al [132], in this volume). In brain astrocytes, gap junction plaques show colocalization of Cx26, Cx30 and Cx43 [116,93].…”

Section: Pattern Of Connexin Expression In the Adult Mammalian Brainmentioning

confidence: 99%

Role of connexin-based gap junction channels and hemichannels in ischemia-induced cell death in nervous tissue

Contreras

Sánchez

Véliz

et al. 2004

Brain Research Reviews

219

185

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Gap junction channels and hemichannels formed of connexin subunits are found in most cell types in vertebrates. Gap junctions connect cells via channels not open to the extracellular space and permit the passage of ions and molecules of ~1 kDa. Single connexin hemichannels, which are connexin hexamers, are present in the surface membrane before docking with a hemichannel in an apposed membrane. Because of their high conductance and permeability in cell-cell channels, it had been thought that connexin hemichannels remained closed until docking to form a cell-cell channel. Now it is clear that at least some hemichannels can open to allow passage of molecules between the cytoplasm and extracellular space. Here we review evidence that gap junction channels may allow intercellular diffusion of necrotic or apoptotic signals, but may also allow diffusion of ions and substances from healthy to injured cells, thereby contributing to cell survival. Moreover, opening of gap junction hemichannels may exacerbate cell injury or mediate paracrine or autocrine signaling. In addition to the cell specific features of an ischemic insult, propagation of cell damage and death within affected tissues may be affected by expression and regulation of gap junction channels and hemichannels formed by connexins.

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“…This could produce substantial changes in the level of a protonated modulator, which would presumably enhance glialglial coupling and spatial buffering during the acute phase of neuronal activity. pH sensitivity of glial and neuronal gap junctions in the nervous system is well established (10), and it is known that in astrocytic gap junctions, Cx26 and Cx43, but not the pH-insensitive Cx32, are present (62).…”

Section: Protonated Taurine Directly Modulates Connexinmentioning

confidence: 99%

Regulation of Connexin Channels by pH

Bevans¹,

Harris

1999

Journal of Biological Chemistry

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Protonated aminosulfonate compounds directly inhibit connexin channel activity. This was demonstrated by pH-dependent connexin channel activity in Good's pH buffers (MES (4-morpholineethanesulfonic acid), HEPES, and TAPS (3-{[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]amino]-1-propanesulfonic acid)) that have an aminosulfonate moiety in common and by the absence of pH-dependent channel activity in pH buffers without an aminosulfonate moiety (maleate, Tris, and bicarbonate). The pH-activity relation was shifted according to the pK a of each aminosulfonate pH buffer. At constant pH, increased aminosulfonate concentration inhibited channel activity. Taurine, a ubiquitous cytoplasmic aminosulfonic acid, had the same effect at physiological concentrations. These data raise the possibility that effects on connexin channel activity previously attributed to protonation of connexin may be mediated instead by protonation of cytoplasmic regulators, such as taurine. Modulation by aminosulfonates is specific for heteromeric connexin channels containing connexin-26; it does not occur significantly for homomeric connexin-32 channels. The identification of taurine as a cytoplasmic compound that directly interacts with and modulates connexin channel activity is likely to facilitate understanding of cellular modulation of connexin channels and lead to the development of reagents for use in structure-function studies of connexin protein. Changes in intracellular pH (pH i )1 affect gap junction conductance between cells (1). The sensitivity of junctional conductance to changes in pH i varies with cell type and connexin isoform (2-5). Decrease of pH i from physiological levels typically produces a decrease in junctional conductance (6 -8) and in permeability to large tracers (9, 10). The decrease in junctional conductance is usually reversible with return of pH i to normal physiological values. The molecular mechanisms that underlie this modulation of connexin channel activity are unclear and may differ among connexin isoforms and cell types. It has been proposed that the modulation is due to direct protonation of connexin (8), changes in ionized calcium concentration (11), and activation of calmodulin (12-14). For connexin-43 and for connexin-32/connexin-38 chimerae, recent work strongly indicates a pH-dependent interaction between segments of the C-terminal domain and the single cytoplasmic loop that inhibits channel activity (3,(15)(16)(17)(18)(19)(20)(21).In this study, we set out to investigate modulation of connexin channel activity as a function of pH, using in a reconstituted system connexin channels immunoaffinity-purified from native tissues. Channel activity was monitored using transport-specific fractionation (TSF) of liposomes into which connexin channels were reconstituted.Channel activity in this system was affected by changes in pH. To our surprise, the changes in channel activity were accounted for by the direct action of the protonated form of the aminosulfonate compounds used as pH buffers, rather than of proton concen...

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Evidence for the co-localization of another connexin with connexin-43 at astrocytic gap junctions in rat brain

Cited by 93 publications

References 35 publications

Direct immunogold labeling of aquaporin-4 in square arrays of astrocyte and ependymocyte plasma membranes in rat brain and spinal cord

Direct immunogold labeling of aquaporin-4 in square arrays of astrocyte and ependymocyte plasma membranes in rat brain and spinal cord

Role of connexin-based gap junction channels and hemichannels in ischemia-induced cell death in nervous tissue

Regulation of Connexin Channels by pH

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