Properties of Connexin26 Hemichannels Expressed in Xenopus Oocytes

Ripps, Harris; Qian, Haohua; Zakevicius, Jane

doi:10.1023/b:cemn.0000036403.43484.3d

Cited by 57 publications

(49 citation statements)

References 65 publications

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“…Control oocytes (H 2 O injected) displayed negligible current flow over a range of voltages from Ϫ30 to ϩ60 mV. Cx26-injected cells exhibited larger outward currents than control cells, confirming previous reports (15,34) of low levels of hemichannel activity. In contrast, oocytes expressing the G45E mutation displayed currents of much greater magnitude in response to depolarization than either control or Cx26-injected cells.…”

Section: G45e Induces Gap Junction Hemichannel Currents In Singlesupporting

confidence: 87%

Aberrant hemichannel properties of Cx26 mutations causing skin disease and deafness

Gerido

DeRosa²,

Richard³

et al. 2007

American Journal of Physiology-Cell Physiology

122

157

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Mutations in the human GJB2 gene, which encodes connexin26 (Cx26), underlie various forms of hereditary deafness and skin disease. While it has proven difficult to discern the exact pathological mechanisms that cause these disorders, studies have shown that the loss or abnormal function of Cx26 protein has a profound effect on tissue homeostasis. Here, we used the Xenopus oocyte expression system to examine the functional characteristics of a Cx26 mutation (G45E) that results in keratitis-ichthyosis-deafness syndrome (KIDS) with a fatal outcome. Our data showed that oocytes were able to express both wild-type Cx26 and its G45E variant, each of which formed hemichannels and gap junction channels. However, Cx26-G45E hemichannels displayed significantly greater whole cell currents than wild-type Cx26, leading to cell lysis and death. This severe phenotype could be rescued in the presence of elevated Ca2+levels in the extracellular milieu. Cx26-G45E could also form intercellular channels with a similar efficiency as wild-type Cx26, however, with increased voltage sensitive gating. We also compared Cx26-G45E with a previously described Cx26 mutant, A40V, which has an overlapping human phenotype. We found that both dominant Cx26 mutants elicited similar functional consequences and that cells coexpressing mutant and wild-type connexins predominantly displayed mutant-like behavior. These data suggest that mutant hemichannels may act on cellular homeostasis in a manner that can be detrimental to the tissues in which they are expressed.

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Section: G45e Induces Gap Junction Hemichannel Currents In Singlesupporting

confidence: 87%

Aberrant hemichannel properties of Cx26 mutations causing skin disease and deafness

Gerido

DeRosa²,

Richard³

et al. 2007

American Journal of Physiology-Cell Physiology

122

157

View full text Add to dashboard Cite

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“…Cx43: 1 mM (41) 100 mM (177) Cx30: 100 mM n/a Cx43: 10 mM-1 mM (227) n/a n/a n/a Zn 2þ n/a Cx46: 10 mM (232) n/a IC 50 % 5 mM (278) n/a 2 mM (227) IC 50 ¼ 11 mM (244) 30 mM (277) NE (279) Extracellular Ca 2þ NE (227) 2 mM (227) NE (227) IC 50 ¼ 2.9 mM (244) n/a Cx26: 3.5 mM (228) Cx26: 2-4 mM (215) Cx32: IC 50 ¼ 107 mM (272) Cx32: EC 50 ¼ 1.3 mM (273) Cx38: 3 mM (280) Cx46: 0.1 mM (274) Cx26, Cx34.7, Cx35, Cx43, Cx27.5, Cx44.1, and Cx55.5: 2 mM (281) Cx50: 5 mM (243) Intracellular Ca 2þ Cx43: IC 50 ¼ 310 nM (282) Cx32: Opened by $500 nM (82) Opened by high…”

Section: Structural Properties Of CX and Panx Channelsmentioning

confidence: 99%

Pannexins, distant relatives of the connexin family with specific cellular functions?

et al. 2009

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Intercellular communication (IC) is mediated by gap junctions (GJs) and hemichannels, which consist of proteins. This has been particularly well documented for the connexin (Cx) family. Initially, Cxs were thought to be the only proteins capable of GJ formation in vertebrates. About 10 years ago, however, a new GJ-forming protein family related to invertebrate innexins (Inxs) was discovered in vertebrates, and named the pannexin (Panx) family. Panxs, which are structurally similar to Cxs, but evolutionarily distinct, have been shown to be co-expressed with Cxs in vertebrates. Both protein families show distinct properties and have their own particular function. Identification of the mechanisms that control Panx channel gating is a major challenge for future work. In this review, we focus on the specific properties and role of Panxs in normal and pathological conditions.

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“…Figure 2A shows current recordings from oocytes expressing human Cx26 in MB and after the addition of various concentrations of zinc. In MB, a voltage ramp from Ϫ100 mV to ϩ60 mV elicited large currents at all potentials positive and negative to the reversal potential (Ϫ10 mV), suggesting that the hemichannels are constitutively open (5). In the presence of low (1 M) concentrations of zinc, the magnitude of the currents through Cx26 hemichannels was substantially enhanced.…”

mentioning

confidence: 98%

Histidine Suppresses Zinc Modulation of Connexin Hemichannels

Chappell

Qian²,

Zakevicius³

et al. 2004

The Biological Bulletin

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Zinc has been shown to modulate hemichannel currents of connexins Cx35 and Cx38 in Xenopus oocytes (1).In both cases the effects were biphasic; i.e., low concentrations of zinc enhanced, whereas higher concentrations decreased, the magnitudes of the voltage-activated hemichannel currents. The present study was designed to determine the effects of zinc on hemichannels formed by Cx26, a connexin reportedly expressed on dendrites of carp horizontal cells and implicated in a mechanism for photoreceptor feedback (2,3,4). In addition, we examined whether histidine, a zinc chelator, would block the action of zinc on Cx26 hemichannel currents, or would exert a direct effect on those currents.Methods for oocyte preparation and recording of connexin hemichannel currents followed procedures described previously (5). Briefly, Stage V-VI oocytes were removed from gravid female Xenopus, enzymatically dissociated and defolliculated, and then used to express human Cx26 connexin in the presence of an antisense oligomer to the endogenous oocyte connexin (Cx38 Voltage-activated membrane currents were recorded with a two-electrode voltage clamp. The two protocols we used gave equivalent results: (1) with the cell clamped at 0 mV, 10-s voltage steps were imposed from Ϫ50 mV to ϩ50 mV in 10-mV increments, and (2) from the holding potential of 0 mV, currents were recorded in response to voltage ramps extending from Ϫ100 mV to ϩ60 mV at a rate of 0.04 mV/ms. Figure 1 compares a representative record from an oocyte expressing Cx26 with those obtained from an antisenseinjected cell and one that was not injected but expressed Cx38, its endogenous connexin. Note the efficacy with which the antisense oligo suppressed the current mediated by Cx38, and the significantly greater membrane currents of Cx26 in response to both depolarizing and hyperpolarizing voltages. Figure 2A shows current recordings from oocytes expressing human Cx26 in MB and after the addition of various concentrations of zinc. In MB, a voltage ramp from Ϫ100 mV to ϩ60 mV elicited large currents at all potentials positive and negative to the reversal potential (Ϫ10 mV), suggesting that the hemichannels are constitutively open (5). In the presence of low (1 M) concentrations of zinc, the magnitude of the currents through Cx26 hemichannels was substantially enhanced. Higher concentrations of zinc, however, decreased these currents in a dose-dependendant fashion such that 10 M zinc reduced the hemichannel currents to the level seen in control MB solution, and 100 M and 1 mM zinc further decreased the hemichannel currents. The bar graphs of Figure 2B, taken from the data in Figure 2A, illustrate the effects of zinc on Cx26 hemichannel currents recorded at ϩ40 mV. Both the enhancement and inhibition by zinc of the Cx26 hemichannel current showed little voltage dependence. As shown in Figure 2C, the ratio of the membrane currents measured in zinc to those recorded in MB were virtually unchanged across the range of membrane voltage tested (from Ϫ100 mV to ϩ60 mV) for both low conc...

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Properties of Connexin26 Hemichannels Expressed in Xenopus Oocytes

Cited by 57 publications

References 65 publications

Aberrant hemichannel properties of Cx26 mutations causing skin disease and deafness

Aberrant hemichannel properties of Cx26 mutations causing skin disease and deafness

Pannexins, distant relatives of the connexin family with specific cellular functions?

Histidine Suppresses Zinc Modulation of Connexin Hemichannels

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