Aberrant CFTR-dependent HCO3- transport in mutations associated with cystic fibrosis.
Cystic fibrosis (CF) is a disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). Initially, Cl- conductance in the sweat duct was discovered to be impaired in CF, a finding that has been extended to all CFTR-expressing cells. Subsequent cloning of the gene showed that CFTR functions as a cyclic-AMP-regulated Cl- channel; and some CF-causing mutations inhibit CFTR Cl- channel activity. The identification of additional CF-causing mutants with normal Cl- channel activity indicates, however, that other CFTR-dependent processes contribute to the disease. Indeed, CFTR regulates other transporters, including Cl(-)-coupled HCO3- transport. Alkaline fluids are secreted by normal tissues, whereas acidic fluids are secreted by mutant CFTR-expressing tissues, indicating the importance of this activity. HCO3- and pH affect mucin viscosity and bacterial binding. We have examined Cl(-)-coupled HCO3- transport by CFTR mutants that retain substantial or normal Cl- channel activity. Here we show that mutants reported to be associated with CF with pancreatic insufficiency do not support HCO3- transport, and those associated with pancreatic sufficiency show reduced HCO3- transport. Our findings demonstrate the importance of HCO3- transport in the function of secretory epithelia and in CF.
Department of Physiology, The University of Texas Southwestern Medical Center, Dallas 75390, USA.
J Y
JY
Choi
D
D
Muallem
K
K
Kiselyov
M G
MG
Lee
P J
PJ
Thomas
S
S
Muallem
D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism; D003550:Cystic Fibrosis / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008564:Membrane Potentials; D008566:Membranes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010179:Pancreas / Q000378:metabolism; D014162:Transfection
D001639:Bicarbonates; C505032:CFTR protein, human; D002712:Chlorides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator