Voltage opens unopposed gap junction hemichannels formed by a connexin 32 mutant associated with X-linked Charcot-Marie-Tooth disease

C. K. Abrams, Michael V. L. Bennett, Vytautas Verselis, T. A. Bargiello

Research output: Contribution to journalArticle

65 Citations (Scopus)

Abstract

The X-linked form of Charcot-Marie-Tooth disease (CMTX) is an inherited peripheral neuropathy that arises in patients with mutations in the gene encoding the gap junction protein connexin 32 (Cx32), which is expressed by Schwann cells. We recently showed that Cx32 containing the CMTX-associated mutation, Ser-85-Cys (S85C), forms functional cell-cell channels in paired Xenopus oocytes. Here, we describe that this mutant connexin also shows increased opening of hemichannels in nonjunctional surface membrane. Open hemichannels may damage the cells through loss of ionic gradients and small metabolites and increased influx of Ca2+, and provide a mechanism by which this and other mutant forms of Cx32 may damage cells in which they are expressed. Evidence for open hemichannels includes: (i) oocytes expressing the Cx32(S85C) mutant show greatly increased conductance at inside positive potentials, significantly larger than in oocytes expressing wild-type Cx32 (Cx32WT); and (ii) the induced currents are similar to those previously described for several other connexin hemichannels, and exhibit slowly developing increases with increasing levels of positivity and reversible reduction when intracellular pH is decreased or extracellular Ca2+ concentration is increased. Although increased currents are seen, oocytes expressing Cx32(S85C) have lower levels of the protein in the surface and in total homogenates than do oocytes expressing Cx32WT; thus, under the conditions examined here, hemichannels in the surface membrane formed of the Cx32(S85C) mutant have a higher open probability than hemichannels formed of Cx32WT. This increase in functional hemichannels may damage Schwann cells and ultimately lead to loss of function in peripheral nerves of patients harboring this mutation.

Original languageEnglish (US)
Pages (from-to)3980-3984
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume99
Issue number6
DOIs
StatePublished - Mar 19 2002

Fingerprint

Charcot-Marie-Tooth Disease
Gap Junctions
Oocytes
Connexins
Schwann Cells
Mutation
Membranes
Xenopus
connexin 32
Peripheral Nerves
Membrane Proteins

ASJC Scopus subject areas

  • Genetics
  • General

Cite this

@article{e4e8b6080d0e40c48bb4c45a01c934cf,
title = "Voltage opens unopposed gap junction hemichannels formed by a connexin 32 mutant associated with X-linked Charcot-Marie-Tooth disease",
abstract = "The X-linked form of Charcot-Marie-Tooth disease (CMTX) is an inherited peripheral neuropathy that arises in patients with mutations in the gene encoding the gap junction protein connexin 32 (Cx32), which is expressed by Schwann cells. We recently showed that Cx32 containing the CMTX-associated mutation, Ser-85-Cys (S85C), forms functional cell-cell channels in paired Xenopus oocytes. Here, we describe that this mutant connexin also shows increased opening of hemichannels in nonjunctional surface membrane. Open hemichannels may damage the cells through loss of ionic gradients and small metabolites and increased influx of Ca2+, and provide a mechanism by which this and other mutant forms of Cx32 may damage cells in which they are expressed. Evidence for open hemichannels includes: (i) oocytes expressing the Cx32(S85C) mutant show greatly increased conductance at inside positive potentials, significantly larger than in oocytes expressing wild-type Cx32 (Cx32WT); and (ii) the induced currents are similar to those previously described for several other connexin hemichannels, and exhibit slowly developing increases with increasing levels of positivity and reversible reduction when intracellular pH is decreased or extracellular Ca2+ concentration is increased. Although increased currents are seen, oocytes expressing Cx32(S85C) have lower levels of the protein in the surface and in total homogenates than do oocytes expressing Cx32WT; thus, under the conditions examined here, hemichannels in the surface membrane formed of the Cx32(S85C) mutant have a higher open probability than hemichannels formed of Cx32WT. This increase in functional hemichannels may damage Schwann cells and ultimately lead to loss of function in peripheral nerves of patients harboring this mutation.",
author = "Abrams, {C. K.} and Bennett, {Michael V. L.} and Vytautas Verselis and Bargiello, {T. A.}",
year = "2002",
month = "3",
day = "19",
doi = "10.1073/pnas.261713499",
language = "English (US)",
volume = "99",
pages = "3980--3984",
journal = "Proceedings of the National Academy of Sciences of the United States of America",
issn = "0027-8424",
number = "6",

}

TY - JOUR

T1 - Voltage opens unopposed gap junction hemichannels formed by a connexin 32 mutant associated with X-linked Charcot-Marie-Tooth disease

AU - Abrams, C. K.

AU - Bennett, Michael V. L.

AU - Verselis, Vytautas

AU - Bargiello, T. A.

PY - 2002/3/19

Y1 - 2002/3/19

N2 - The X-linked form of Charcot-Marie-Tooth disease (CMTX) is an inherited peripheral neuropathy that arises in patients with mutations in the gene encoding the gap junction protein connexin 32 (Cx32), which is expressed by Schwann cells. We recently showed that Cx32 containing the CMTX-associated mutation, Ser-85-Cys (S85C), forms functional cell-cell channels in paired Xenopus oocytes. Here, we describe that this mutant connexin also shows increased opening of hemichannels in nonjunctional surface membrane. Open hemichannels may damage the cells through loss of ionic gradients and small metabolites and increased influx of Ca2+, and provide a mechanism by which this and other mutant forms of Cx32 may damage cells in which they are expressed. Evidence for open hemichannels includes: (i) oocytes expressing the Cx32(S85C) mutant show greatly increased conductance at inside positive potentials, significantly larger than in oocytes expressing wild-type Cx32 (Cx32WT); and (ii) the induced currents are similar to those previously described for several other connexin hemichannels, and exhibit slowly developing increases with increasing levels of positivity and reversible reduction when intracellular pH is decreased or extracellular Ca2+ concentration is increased. Although increased currents are seen, oocytes expressing Cx32(S85C) have lower levels of the protein in the surface and in total homogenates than do oocytes expressing Cx32WT; thus, under the conditions examined here, hemichannels in the surface membrane formed of the Cx32(S85C) mutant have a higher open probability than hemichannels formed of Cx32WT. This increase in functional hemichannels may damage Schwann cells and ultimately lead to loss of function in peripheral nerves of patients harboring this mutation.

AB - The X-linked form of Charcot-Marie-Tooth disease (CMTX) is an inherited peripheral neuropathy that arises in patients with mutations in the gene encoding the gap junction protein connexin 32 (Cx32), which is expressed by Schwann cells. We recently showed that Cx32 containing the CMTX-associated mutation, Ser-85-Cys (S85C), forms functional cell-cell channels in paired Xenopus oocytes. Here, we describe that this mutant connexin also shows increased opening of hemichannels in nonjunctional surface membrane. Open hemichannels may damage the cells through loss of ionic gradients and small metabolites and increased influx of Ca2+, and provide a mechanism by which this and other mutant forms of Cx32 may damage cells in which they are expressed. Evidence for open hemichannels includes: (i) oocytes expressing the Cx32(S85C) mutant show greatly increased conductance at inside positive potentials, significantly larger than in oocytes expressing wild-type Cx32 (Cx32WT); and (ii) the induced currents are similar to those previously described for several other connexin hemichannels, and exhibit slowly developing increases with increasing levels of positivity and reversible reduction when intracellular pH is decreased or extracellular Ca2+ concentration is increased. Although increased currents are seen, oocytes expressing Cx32(S85C) have lower levels of the protein in the surface and in total homogenates than do oocytes expressing Cx32WT; thus, under the conditions examined here, hemichannels in the surface membrane formed of the Cx32(S85C) mutant have a higher open probability than hemichannels formed of Cx32WT. This increase in functional hemichannels may damage Schwann cells and ultimately lead to loss of function in peripheral nerves of patients harboring this mutation.

UR - http://www.scopus.com/inward/record.url?scp=0037133669&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0037133669&partnerID=8YFLogxK

U2 - 10.1073/pnas.261713499

DO - 10.1073/pnas.261713499

M3 - Article

C2 - 11891346

AN - SCOPUS:0037133669

VL - 99

SP - 3980

EP - 3984

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

SN - 0027-8424

IS - 6

ER -