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Opposing modulation of Cx26 gap junctions and hemichannels by CO2.

Nijjar, Sarbjit and Maddison, Daniel and Meigh, Louise and Wolf, Elizabeth and Rodgers, Thomas and Cann, Martin and Dale, Nicholas (2020) 'Opposing modulation of Cx26 gap junctions and hemichannels by CO2.', Journal of physiology .

Abstract

Cx26 hemichannels open in response to moderate elevations of CO2 (PCO2 55 mmHg) via a carbamylation reaction that depends on residues K125 and R104. Here we investigate the action of CO2 on Cx26 gap junctions. Using a dye transfer assay, we found that an elevated PCO2 of 55 mmHg greatly delayed the permeation of a fluorescent glucose analogue (NBDG) between HeLa cells coupled by Cx26 gap junctions. However, the mutations K125R or R104A abolished this effect of CO2. Whole cell recordings demonstrated that elevated CO2 reduced the Cx26 gap junction conductance (median reduction 66.7%, 95% confidence interval, 50.5 to 100.0%) but had no effect on Cx26K125R or Cx31 gap junctions. CO2 can cause intracellular acidification. Using 30 mM propionate, we found that acidification in the absence of a change in PCO2 caused a median reduction in the gap junction conductance of 41.7% (26.6 to 53.7%). This effect of propionate was unaffected by the K125R mutation (median reduction 48.1%, 28.0 to 86.3%). pH‐dependent and CO2‐dependent closure of the gap junction are thus mechanistically independent. Mutations of Cx26 associated with the Keratitis Ichthyosis Deafness syndrome (N14K, A40V and A88V), in combination with the mutation M151L, also abolished the CO2‐dependent gap junction closure. Elastic network modelling suggests that the lowest entropy state when CO2 is bound, is the closed configuration for the gap junction but the open state for the hemichannel. The opposing actions of CO2 on Cx26 gap junctions and hemichannels thus depend on the same residues and presumed carbamylation reaction.

Item Type:Article
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Available under License - Creative Commons Attribution.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1113/JP280747
Publisher statement:© 2020 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Date accepted:02 October 2020
Date deposited:04 November 2020
Date of first online publication:06 October 2020
Date first made open access:04 November 2020

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