Xenopus connexin38 forms hemi-gap-junctional channels in the nonjunctional plasma membrane of Xenopus oocytes

Ebihara, Lisa

doi:10.1016/s0006-3495(96)79273-1

Cited by 140 publications

(127 citation statements)

References 27 publications

(32 reference statements)

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“…The two-state distribution of the inner pore diameters (ϳ2.5 and ϳ1.8 nm) indicates a two- [Ca 2ϩ ] o mechanism that opens and closes connexons. This is consistent with previous functional studies of hemichannel and its physiological role (17,22,27); in response to extracellular calcium, a single hemichannel switches between open and closed steady states with the open/close probability being [Ca 2ϩ ]-dependent. In ϳ10% of open or closed connexons, we were able to resolve subunit topology of individual connexins (Fig.…”

Section: Ca 2ϩ -Dependent Conformations and Energetics Of Hemichannelssupporting

confidence: 92%

“…The closed pore diameter remained statistically unaltered for a series of calcium concentrations and was unlikely affected by the noise in the AFM imaging; we only analyzed structures for which repeatable images were collected. The two-state distribution of the inner pore diameters (ϳ2.5 and ϳ1.8 nm) suggests an all-or-none opening mechanism and is consistent with previous functional studies of hemichannel and its physiological role (17,22,27); a single hemichannel switches between open and closed states in an all-or-none manner, and the open/close probability is [Ca 2ϩ ]-dependent. It is possible that statistically non-significant fluctuations in the pore diameter (Fig.…”

Section: Cytoplasmic Versus Extracellular Side Of Reconstituted Cx43supporting

confidence: 89%

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Calcium-dependent Open/Closed Conformations and Interfacial Energy Maps of Reconstituted Hemichannels

Thimm

Mechler

Lin

et al. 2005

Journal of Biological Chemistry

157

127

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Using an atomic force microscope, we have studied threedimensional molecular topography and calcium-sensitive conformational changes of individual hemichannels. Fulllength (non-truncated) Cx43 hemichannels (connexons), when reconstituted in lipid bilayer, appear as randomly distributed individual particles and clusters. They show a lack of preferential orientation of insertion into lipid membrane; in a single bilayer, connexons with protrusion of either the extracellular face or the large non-truncated cytoplasmic face are observed. Extracellular domains of these undocked hemichannels are structurally different from hemichannels in the docked gap junctional plaques examined after their exposure by force dissection or chemical dissection. Calcium induced a reversible change in the extracellular pore diameter. Hemichannels imaged in a physiological buffer with 1.8 mM Ca ؉2 had the pore diameter of ϳ1.8 nm, consistent with the closed channel conformation. Reducing Ca ؉2 concentration to ϳ1.4, 1, and 0 mM, which changes hemichannels from the closed to open conformation, increased the pore diameter to ϳ2.5 nm for ϳ27, 74, and 100% of hemichannels, respectively. Thus, open/close probability of the hemichannel appears to be [Ca 2؉ ]-dependent. Computational analysis of the atomic force microscopy phase mode imaging reveals a significantly higher interfacial energy for open hemichannels that results from the interactions between the atomic force microscope probe and the hydrophobic domains. Thus, hydrophobic extracellular domains of connexins regulate calcium-dependent conformational changes.

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Section: Ca 2ϩ -Dependent Conformations and Energetics Of Hemichannelssupporting

confidence: 92%

Section: Cytoplasmic Versus Extracellular Side Of Reconstituted Cx43supporting

confidence: 89%

Calcium-dependent Open/Closed Conformations and Interfacial Energy Maps of Reconstituted Hemichannels

Thimm

Mechler

Lin

et al. 2005

Journal of Biological Chemistry

157

127

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“…Because this channel is half of a gap junction channel, it is referred to as a ''hemichannel.'' Hemichannel function has been described also for some connexins under certain experimental conditions (18)(19)(20)(21)(22). In particular, Cx43 has been implicated as an ATP release channel (9,23,24), although calcium wave propagation was found to proceed in Cx43-deficient cells at normal rates (25,26).…”

Section: Discussionmentioning

confidence: 99%

Pannexin 1 in erythrocytes: Function without a gap

Locovei

Dahl

2006

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

469

644

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ATP is a widely used extracellular signaling molecule. The mechanism of ATP release from cells is presently unresolved and may be either vesicular or channel-mediated. Erythrocytes release ATP in response to low oxygen or to shear stress. In the absence of vesicles, the release has to be through channels. Erythrocytes do not form gap junctions. Yet, here we show with immunohistochemical and electrophysiological data that erythrocytes express the gap junction protein pannexin 1. This protein, in addition to forming gap junction channels in paired oocytes, can also form a mechanosensitive and ATP-permeable channel in the nonjunctional plasma membrane. Consistent with a role of pannexin 1 as an ATP release channel, ATP release by erythrocytes was attenuated by the gap junction blocker carbenoxolone. Furthermore, under conditions of ATP release, erythrocytes took up fluorescent tracer molecules permeant to gap junction channels.ATP release ͉ gap junction ͉ hemichannel ͉ dye uptake P annexins represent a recently discovered second family of gap junction proteins in vertebrates (1). Pannexins have no sequence homology with the well known connexin family of vertebrate gap junction proteins. Instead, they are related to innexins, which were originally considered to be exclusively invertebrate gap junction proteins. The functional role of pannexins is unknown. The existence of connexin-specific diseases, despite an overlap of connexin and pannexin expression, suggests a functional role of pannexins that is distinct from that of connexins. Pannexin 1, in addition to forming gap junctions in paired oocytes, also forms nonjunctional membrane channels that provide a passageway from the cytoplasm to the extracellular space for molecules in the size range of second messengers (2, 3). It can be hypothesized that the physiological role of pannexin 1 is formation of a nonjunctional membrane channel.Although the role of ATP as an extracellular signaling molecule is well recognized (4), the release mechanism for ATP from cells to the extracellular space has remained enigmatic. Two general release modes have been proposed: (i) vesicular release akin to the exocytotic release of transmitters and (ii) channel-mediated release. Although vesicular ATP release is well documented (5, 6), it cannot account for all of the ATP release phenomena. In particular, ATP is released from erythrocytes, which, under physiological conditions, are vesicle-free (7). Various channels have been implicated in the process, including CFTR (cystic fibrosis transmembrane conductance regulator), connexin 43 (Cx43) hemichannels, a volumeregulated channel (VRAC), and the purinergic receptor P2X7 (5,6,(8)(9)(10)(11). However, the evidence for their involvement falls short because of questionable specificity of the pharmacological blockers used to determine channel identity.Mechanical stress is a prime stimulus for ATP release in many cell types, including erythrocytes (12). An efficient release mechanism thus may involve a channel that is both mechanosensitive and...

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“…Oocytes were defolliculated by treatment with collagenase (Worthington). At least 2 h after collagenase treatment, 1-5 ng of CALHM1 cRNA was injected into oocytes with 80 ng of Xenopus connexin 38 antisense oligonucleotide to inhibit endogenous connexin 38 (Cx38) currents (3,6,7). Oocytes were kept at 16°C in a ND96 solution (96 mM NaCl, 2 mM KCl, 1.8 mM CaCl 2 , 1 mM MgCl 2 , 2.5 mM sodium pyruvate, 5 mM HEPES, 1ϫ penicillin/streptomycin, pH 7.6 (adjusted by NaOH)).…”

Section: Methodsmentioning

confidence: 99%

Structural and Functional Similarities of Calcium Homeostasis Modulator 1 (CALHM1) Ion Channel with Connexins, Pannexins, and Innexins*

Siebert¹,

Ma²,

Grevet³

et al. 2013

Journal of Biological Chemistry

109

122

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Background: CALHM1 is an ion channel for which structural information is lacking. Results: CALHM1 has poor ion selectivity and a wide (ϳ14 Å) pore and is a hexamer, with monomers having four transmembrane domains with cytoplasmic termini. Conclusion: CALHM1 shares structural features with pannexins, connexins, and innexins. Significance: CALHMs, connexins, and pannexins/innexins are three structurally related protein families with shared and distinct functional properties.

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Xenopus connexin38 forms hemi-gap-junctional channels in the nonjunctional plasma membrane of Xenopus oocytes

Cited by 140 publications

References 27 publications

Calcium-dependent Open/Closed Conformations and Interfacial Energy Maps of Reconstituted Hemichannels

Calcium-dependent Open/Closed Conformations and Interfacial Energy Maps of Reconstituted Hemichannels

Pannexin 1 in erythrocytes: Function without a gap

Structural and Functional Similarities of Calcium Homeostasis Modulator 1 (CALHM1) Ion Channel with Connexins, Pannexins, and Innexins*

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