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Am J Physiol Cell Physiol 275: C1113-C1123, 1998;
0363-6143/98 $5.00
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Vol. 275, Issue 4, C1113-C1123, October 1998

Identification of the pH sensor and activation by chemical modification of the ClC-2G Clminus channel

Katarina Stroffekova1, Elena Y. Kupert1, Danuta H. Malinowska1, and John Cuppoletti1,2

1 Department of Molecular and Cellular Physiology and 2 Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0576

Rabbit and human ClC-2G Cl- channels are voltage sensitive and activated by protein kinase A and low extracellular pH. The objective of the present study was to investigate the mechanism involved in acid activation of the ClC-2G Cl- channel and to determine which amino acid residues play a role in this acid activation. Channel open probability (Po) at ±80 mV holding potentials increased fourfold in a concentration-dependent manner with extracellular H+ concentration (that is, extracellular pH, pHtrans), with an apparent acidic dissociation constant of pH 4.95 ± 0.27. 1-Ethyl-3(3-dimethylaminopropyl)carbodiimide-catalyzed amidation of the channel with glycine methyl ester increased Po threefold at pHtrans 7.4, at which the channel normally exhibits low Po. With extracellular pH reduction (protonation) or amidation, increased Po was due to a significant increase in open time constants and a significant decrease in closed time constants of the channel gating, and this effect was insensitive to applied voltage. With the use of site-directed mutagenesis, the extracellular region EELE (amino acids 416-419) was identified as the pH sensor and amino acid Glu-419 was found to play the key or predominant role in activation of the ClC-2G Cl- channel by extracellular acid.

human and rabbit chloride channels; Xenopus laevis oocytes; cystic fibrosis; acid-activated chloride channel; protein kinase-regulated chloride channel; protein kinase A; gastric secretion; epithelial transport; chloride transport; water-soluble carbodiimide; amidation


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