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Volume-regulated Anion Channels Serve as an Auto/Paracrine Nucleotide Release Pathway in Aortic Endothelial Cells

Volume-regulated Anion Channels Serve as an Auto/Paracrine Nucleotide Release Pathway in Aortic... Mechanical stress induces auto/paracrine ATP release from various cell types, but the mechanisms underlying this release are not well understood. Here we show that the release of ATP induced by hypotonic stress (HTS) in bovine aortic endothelial cells (BAECs) occurs through volume-regulated anion channels (VRAC). Various VRAC inhibitors, such as glibenclamide, verapamil, tamoxifen, and fluoxetine, suppressed the HTS-induced release of ATP, as well as the concomitant Ca 2+ oscillations and NO production. They did not, however, affect Ca 2+ oscillations and NO production induced by exogenously applied ATP. Extracellular ATP inhibited VRAC currents in a voltage-dependent manner: block was absent at negative potentials and was manifest at positive potentials, but decreased at highly depolarized potentials. This phenomenon could be described with a “permeating blocker model,” in which ATP binds with an affinity of 1.0 ± 0.5 mM at 0 mV to a site at an electrical distance of 0.41 inside the channel. Bound ATP occludes the channel at moderate positive potentials, but permeates into the cytosol at more depolarized potentials. The triphosphate nucleotides UTP, GTP, and CTP, and the adenine nucleotide ADP, exerted a similar voltage-dependent inhibition of VRAC currents at submillimolar concentrations, which could also be described with this model. However, inhibition by ADP was less voltage sensitive, whereas adenosine did not affect VRAC currents, suggesting that the negative charges of the nucleotides are essential for their inhibitory action. The observation that high concentrations of extracellular ADP enhanced the outward component of the VRAC current in low Cl − hypotonic solution and shifted its reversal potential to negative potentials provides more direct evidence for the nucleotide permeability of VRAC. We conclude from these observations that VRAC is a nucleotide-permeable channel, which may serve as a pathway for HTS-induced ATP release in BAEC. ATP release nitric oxide hypotonic stress volume-regulated anion channel calcium Footnotes ↵ * Abbreviations used in this paper: BAEC, bovine aortic endothelial cell; DAF-2, diaminofluorescein-2; HTS, hypotonic stress; VRAC, volume-regulated anion channels. Submitted: 5 December 2001 Accepted: 22 April 2002 Revision received 8 April 2002 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of General Physiology Rockefeller University Press

Volume-regulated Anion Channels Serve as an Auto/Paracrine Nucleotide Release Pathway in Aortic Endothelial Cells

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Publisher
Rockefeller University Press
Copyright
Copyright © 2002, by The Rockefeller University Press
ISSN
0022-1295
eISSN
1540-7748
DOI
10.1085/jgp.20028540
Publisher site
See Article on Publisher Site

Abstract

Mechanical stress induces auto/paracrine ATP release from various cell types, but the mechanisms underlying this release are not well understood. Here we show that the release of ATP induced by hypotonic stress (HTS) in bovine aortic endothelial cells (BAECs) occurs through volume-regulated anion channels (VRAC). Various VRAC inhibitors, such as glibenclamide, verapamil, tamoxifen, and fluoxetine, suppressed the HTS-induced release of ATP, as well as the concomitant Ca 2+ oscillations and NO production. They did not, however, affect Ca 2+ oscillations and NO production induced by exogenously applied ATP. Extracellular ATP inhibited VRAC currents in a voltage-dependent manner: block was absent at negative potentials and was manifest at positive potentials, but decreased at highly depolarized potentials. This phenomenon could be described with a “permeating blocker model,” in which ATP binds with an affinity of 1.0 ± 0.5 mM at 0 mV to a site at an electrical distance of 0.41 inside the channel. Bound ATP occludes the channel at moderate positive potentials, but permeates into the cytosol at more depolarized potentials. The triphosphate nucleotides UTP, GTP, and CTP, and the adenine nucleotide ADP, exerted a similar voltage-dependent inhibition of VRAC currents at submillimolar concentrations, which could also be described with this model. However, inhibition by ADP was less voltage sensitive, whereas adenosine did not affect VRAC currents, suggesting that the negative charges of the nucleotides are essential for their inhibitory action. The observation that high concentrations of extracellular ADP enhanced the outward component of the VRAC current in low Cl − hypotonic solution and shifted its reversal potential to negative potentials provides more direct evidence for the nucleotide permeability of VRAC. We conclude from these observations that VRAC is a nucleotide-permeable channel, which may serve as a pathway for HTS-induced ATP release in BAEC. ATP release nitric oxide hypotonic stress volume-regulated anion channel calcium Footnotes ↵ * Abbreviations used in this paper: BAEC, bovine aortic endothelial cell; DAF-2, diaminofluorescein-2; HTS, hypotonic stress; VRAC, volume-regulated anion channels. Submitted: 5 December 2001 Accepted: 22 April 2002 Revision received 8 April 2002

Journal

The Journal of General Physiology – Rockefeller University Press

Published: Jun 1, 2002

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