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Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ.

Publication ,  Journal Article
Pohl, P; Saparov, SM; Borgnia, MJ; Agre, P
Published in: Proc Natl Acad Sci U S A
August 14, 2001

Aquaporins are membrane channels selectively permeated by water or water plus glycerol. Conflicting reports have described ion conductance associated with some water channels, raising the question of whether ion conductance is a general property of the aquaporin family. To clarify this question, a defined system was developed to simultaneously measure water permeability and ion conductance. The Escherichia coli water channel aquaporin-Z (AqpZ) was studied, because it is a highly stable tetramer. Planar lipid bilayers were formed from unilamellar vesicles containing purified AqpZ. The hydraulic conductivity of bilayers made from the total extract of E. coli lipids increased 3-fold if reconstituted with AqpZ, but electric conductance was unchanged. No channel activity was detected under voltage-clamp conditions, indicating that less than one in 10(9) transport events is electrogenic. Microelectrode measurements were simultaneously undertaken adjacent to the membrane. Changes in sodium concentration profiles accompanying transmembrane water flow permitted calculation of the activation energies: 14 kcal/mol for protein-free lipid bilayers and 4 kcal/mol for lipid bilayers containing AqpZ. Neither the water permeability nor the electric conductivity exhibited voltage dependence. This sensitive system demonstrated that AqpZ is permeated by water but not charged ions and should permit direct analyses of putative electrogenic properties of other aquaporins.

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Published In

Proc Natl Acad Sci U S A

DOI

ISSN

0027-8424

Publication Date

August 14, 2001

Volume

98

Issue

17

Start / End Page

9624 / 9629

Location

United States

Related Subject Headings

  • Water
  • Static Electricity
  • Recombinant Fusion Proteins
  • Proteolipids
  • Protein Conformation
  • Permeability
  • Patch-Clamp Techniques
  • Microelectrodes
  • Membrane Proteins
  • Membrane Potentials
 

Citation

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Pohl, P., Saparov, S. M., Borgnia, M. J., & Agre, P. (2001). Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ. Proc Natl Acad Sci U S A, 98(17), 9624–9629. https://doi.org/10.1073/pnas.161299398
Pohl, P., S. M. Saparov, M. J. Borgnia, and P. Agre. “Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ.Proc Natl Acad Sci U S A 98, no. 17 (August 14, 2001): 9624–29. https://doi.org/10.1073/pnas.161299398.
Pohl P, Saparov SM, Borgnia MJ, Agre P. Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ. Proc Natl Acad Sci U S A. 2001 Aug 14;98(17):9624–9.
Pohl, P., et al. “Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ.Proc Natl Acad Sci U S A, vol. 98, no. 17, Aug. 2001, pp. 9624–29. Pubmed, doi:10.1073/pnas.161299398.
Pohl P, Saparov SM, Borgnia MJ, Agre P. Highly selective water channel activity measured by voltage clamp: analysis of planar lipid bilayers reconstituted with purified AqpZ. Proc Natl Acad Sci U S A. 2001 Aug 14;98(17):9624–9629.
Journal cover image

Published In

Proc Natl Acad Sci U S A

DOI

ISSN

0027-8424

Publication Date

August 14, 2001

Volume

98

Issue

17

Start / End Page

9624 / 9629

Location

United States

Related Subject Headings

  • Water
  • Static Electricity
  • Recombinant Fusion Proteins
  • Proteolipids
  • Protein Conformation
  • Permeability
  • Patch-Clamp Techniques
  • Microelectrodes
  • Membrane Proteins
  • Membrane Potentials