Changes in lens connexin expression lead to increased gap junctional voltage dependence and conductance

Donaldson, Paul J.; Dong, Ying; Roos, Marc; Green, C.; Goodenough, D A; Kistler, Joerg

doi:10.1152/ajpcell.1995.269.3.c590

Cited by 60 publications

(38 citation statements)

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“…Interestingly, this value is very similar to the 210-pS channel detected in mouse lens fiber cells by Donaldson et al (1995). The open-probability for human Cx50 channels was near 1 at low V j S and was greatly decreased with increasing V j , similar to the results reported for mouse Cx50 channels (Srinivas et al, 1999).…”

Section: Discussionsupporting

confidence: 86%

Functional Role of the Carboxyl Terminal Domain of Human Connexin 50 in Gap Junctional Channels

Berthoud

Beyer

et al. 2002

Journal of Membrane Biology

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Gap junction channels formed by connexin 50 (Cx50) are critical for maintenance of lens transparency. Because the C-terminus of Cx50 can be cleaved post-translationally, we hypothesized that channels formed by the truncated Cx50 exhibit altered properties or regulation. We used the dual whole-cell patch-clamp technique to investigate the macroscopic and single-channel properties of gap junctional channels formed by wild-type human Cx50 and a truncation mutant (Cx50A294stop) after transfection of N2A cells. Our results show that wild-type Cx50 formed functional gap junctional channels. The macroscopic G jss -V j relationship was well described by a Boltzmann equation with A of 0.10, V 0 of 43.8 mV and G jmin of 0.23. The single-channel conductance was 212 ± 5 pS. Multiple long-lasting substates were observed with conductances ranging between 31 and 80 pS. Wild-type Cx50 gap junctional channels were reversibly blocked when pH i was reduced to 6.3. Truncating the C-terminus at amino acid 294 caused a loss of pH i sensitivity, but there were no significant changes in single-channel current amplitude or G jss -V j relationship. These results suggest that the C-terminus of human Cx50 is involved in pH i sensitivity, but has little influence over singlechannel conductance, voltage dependence, or gating kinetics.

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Section: Discussionsupporting

confidence: 86%

Functional Role of the Carboxyl Terminal Domain of Human Connexin 50 in Gap Junctional Channels

Berthoud

Beyer

et al. 2002

Journal of Membrane Biology

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“…SPARC mRNA was present in both lens epithelial cells and in fiber cells ( Figure 3G). Connexin 43 (Cx43) was expressed specifically in the undifferentiated lens epithelial cells and not in fiber cells (Donaldson et al 1995). Therefore, Cx43 was used to detect epithelial cell contamination of the fiber cell isolates used for RT-PCR.…”

Section: Cellular Localization Of Sparc In Lens Epithelial Cells and mentioning

confidence: 99%

Expression of the Matricellular Protein SPARC in Murine Lens: SPARC Is Necessary for the Structural Integrity of the Capsular Basement Membrane

Yan

Blake

Clark

et al. 2003

J Histochem Cytochem.

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S U M M A R Y SPARC (Secreted Protein, Acidic and Rich in Cysteine) is a matricellular glycoprotein that modulates cell proliferation, adhesion, migration, and extracellular matrix (ECM) production. Although SPARC is generally abundant in embryonic tissues and is diminished in adults, we have found that the expression of SPARC in murine lens persists throughout embryogenesis and adulthood. Our previous studies showed that targeted ablation of the SPARC gene in mice results in cataract formation, a pathology attributed partially to an abnormal lens capsule. Here we provide evidence that SPARC is not a structural component of the lens capsule. In contrast, SPARC is abundant in lens epithelial cells, and newly differentiated fiber cells, with stable expression in wild-type mice up to 2 years of age. Pertubation of the lens capsule in animals lacking SPARC appears to be a consequence of the invasion of the lens cells situated beneath the capsule. Immunoreactivity for SPARC in the lens cells was uneven, with minimal reactivity in the epithelial cells immediately anterior to the equator. These epithelial cells appeared essentially noninvasive in SPARC-null mice, in comparison to the centrally located anterior epithelial cells, in which strong labeling by anti-SPARC IgG was observed. The posterior lens fibers exhibited cytoplasmic extensions into the posterior lens capsule, which was severely damaged in SPARC-null lenses. The expression of SPARC in wild-type lens cells, together with the abnormal lens capsule in SPARC-null mice, indicated that the structural integrity of the lens capsule is dependent on the matricellular protein SPARC. The effects of SPARC in the lens appear to involve regulation of lens epithelial and fiber cell morphology and functions rather than deposition as a structural component of the lens capsule.

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“…Neighboring cells may contribute heteromeric or homomeric connexons to form complete intercellular channels known as homotypic (the combination of two identical uniform connexons), heteromeric (the association of two hemichannels varying in connexin expression), and heterotypic channels (the alignment of two connexons each containing a single unique connexin). Recent studies have shown that altering the connexin composition of gap junctions changes both the permeability and electrophysiological properties of these channels in vitro (Bevans et al, 1998;Cao et al, 1998;Donaldson et al, 1995;Goldberg et al, 1999;Niessen et al, 2000;Valiunas et al, 2002;Veenstra, 1996;White, 2003;White and Bruzzone, 1996).…”

Section: Introductionmentioning

confidence: 99%

“…Conversely, Cx50 is present in both, the epithelium and differentiated fibers (Rong et al, 2002;White et al, 1992). This overlapping, yet distinct, pattern of connexin expression contributes to a variation in junctional communication based on the connexin composition in specific cell types (Donaldson et al, 2001;Donaldson et al, 1995;Mathias et al, 1997).…”

Section: Introductionmentioning

confidence: 99%

The cataract-inducing S50P mutation in Cx50 dominantly alters the channel gating of wild-type lens connexins

DeRosa

Xia

Gong

et al. 2007

Journal of Cell Science

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Mutations within connexin50 (Cx50) have been linked to various cataract phenotypes. To determine the mechanism behind cataract formation we used the paired Xenopus oocyte system in conjunction with transfected HeLa cells and genetically engineered mouse models to examine the functional characteristics of gap junctions in which a cataract-causing mutant of Cx50 (hereafter referred to as Cx50-S50P) is expressed. Channels comprising Cx50-S50P subunits alone failed to induce electrical coupling. However, the mixed expression of Cx50-S50P and wild-type subunits of either Cx50 or Cx46 – to create heteromeric gap junctions – resulted in functional intercellular channels with altered voltage-gating properties compared with homotypic wild-type channels. Additionally, immunofluorescence microscopy showed that channels of Cx50-S50P subunits alone failed to localize to the plasma membrane – unlike channels composed of Cx46 subunits, which concentrated at cell-cell appositions. Cx50-S50P colocalized with wild-type Cx46 in both transfected HeLa cells in vitro and mouse lens sections in vivo. Taken together, these data define the electrophysiological properties and intracellular targeting of gap junctions formed by the heteromeric combination of Cx50 or Cx46 and Cx50-S50P mutant proteins. Additionally, mixed channels displayed significantly altered gating properties, a phenomenon that may contribute to the cataract that is associated with this mutation.

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Changes in lens connexin expression lead to increased gap junctional voltage dependence and conductance

Cited by 60 publications

References 1 publication

Functional Role of the Carboxyl Terminal Domain of Human Connexin 50 in Gap Junctional Channels

Functional Role of the Carboxyl Terminal Domain of Human Connexin 50 in Gap Junctional Channels

Expression of the Matricellular Protein SPARC in Murine Lens: SPARC Is Necessary for the Structural Integrity of the Capsular Basement Membrane

The cataract-inducing S50P mutation in Cx50 dominantly alters the channel gating of wild-type lens connexins

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