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Opposing modulation of Cx26 gap junctions and hemichannels by CO 2

Nijjar, Sarbjit, Maddison, Daniel, Meigh, Louise, Wolf, Elizabeth, Rodgers, Thomas, Cann, Martin J. and Dale, Nicholas 2021. Opposing modulation of Cx26 gap junctions and hemichannels by CO 2. Journal of Physiology 599 (1) , pp. 103-118. 10.1113/JP280747

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Cx26 hemichannels open in response to moderate elevations of CO2 (urn:x-wiley:00223751:media:tjp14422:tjp14422-math-0002 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 urn:x-wiley:00223751:media:tjp14422:tjp14422-math-0003 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% CI, 50.5–100.0%) 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 urn:x-wiley:00223751:media:tjp14422:tjp14422-math-0004 caused a median reduction in the gap junction conductance of 41.7% (95% CI, 26.6–53.7%). This effect of propionate was unaffected by the K125R mutation (median reduction 48.1%, 95% CI, 28.0–86.3%). 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
Date Type: Publication
Status: Published
Schools: Medicine
Additional Information: This is an open access article under the terms of the Creative Commons Attribution License
Publisher: Wiley
ISSN: 0022-3751
Date of First Compliant Deposit: 7 July 2022
Date of Acceptance: 2 October 2020
Last Modified: 07 Jul 2022 13:30

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