Abstract.
We have investigated the effects of extracellular and intracellular pH on single channel and macroscopic (macropatches) currents through volume-regulated anion channels (VRAC) in endothelial cells.
Protonation of extracellular binding sites with an apparent pK of 4.6 increased voltage independent of the single-channel amplitude. Cytosolic acidification had a dual effect on VRAC currents: on the one hand, it increased single channel conductance by ∼20% due to protonation of a group with an apparent pK of 6.5 and a Hill coefficient of 2. On the other hand, it reduced channel activity due to protonation of a group with an apparent pK of 6.3 and a Hill coefficient of 2.1. This dual effect enhances the macroscopic current at a slightly acidic pH but inhibits it at more acidic pH. Cytosolic alkalization also reduced channel activity with a pK of 8.4 and a Hill coefficient of 1.9, but apparently did not affect single-channel conductance.
These data show that VRAC channels are maintained in an active state in a narrow pH range around the normal physiological pH and shut down outside this range. They also show that HEPES-buffered pipette solutions do not effectively buffer pH in the vicinity of the VRAC channels.
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Received: 31 January 2000/Revised: 21 April 2000
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Sabirov, R., Prenen, J., Droogmans, G. et al. Extra- and Intracellular Proton-Binding Sites of Volume-Regulated Anion Channels. J. Membrane Biol. 177, 13–22 (2000). https://doi.org/10.1007/s002320001090
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DOI: https://doi.org/10.1007/s002320001090