TY - JOUR
T1 - Interactions between impermeant blocking ions in the cystic fibrosis transmembrane conductance regulator chloride channel pore
T2 - Evidence for anion-induced conformational changes
AU - Ge, Ning
AU - Linsdell, Paul
PY - 2006/3
Y1 - 2006/3
N2 - It is well known that extracellular Cl- ions can weaken the inhibitory effects of intracellular open channel blockers in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel pore. This effect is frequently attributed to repulsive ion-ion interactions inside the pore. However, since Cl- ions are permeant in CFTR, it is also possible that extracellular Cl- ions are directly competing with intracellular blocking ions for a common binding site; thus, this does not provide direct evidence for multiple, independent anion binding sites in the pore. To test for the possible through-space nature of ion-ion interactions inside the CFTR pore, we investigated the interaction between impermeant anions applied to either end of the pore. We found that inclusion of low concentrations of impermeant Pt(NO2) 4 2- ions in the extracellular solution weaken the blocking effects of three different intracellular blockers [Pt(NO2) 4 2- , glibenclamide and 5-nitro-2-(3-phenylpropylamino)benzoic acid] without affecting their apparent voltage dependence. However, the effects of extracellular Pt(NO2) 4 2- ions are too strong to be accounted for by simple competitive models of ion binding inside the pore. In addition, extracellular Fe(CN) 6 3- ions, which do not appear to enter the pore, also weaken the blocking effects of intracellular Pt(NO2) 4 2- ions. In contrast to previous models that invoked interactions between anions bound concurrently inside the pore, we propose that Pt(NO2) 4 2- and Fe(CN) 6 3- binding to an extracellularly accessible site outside of the channel permeation pathway alters the structure of an intracellular anion binding site, leading to weakened binding of intracellular blocking ions.
AB - It is well known that extracellular Cl- ions can weaken the inhibitory effects of intracellular open channel blockers in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel pore. This effect is frequently attributed to repulsive ion-ion interactions inside the pore. However, since Cl- ions are permeant in CFTR, it is also possible that extracellular Cl- ions are directly competing with intracellular blocking ions for a common binding site; thus, this does not provide direct evidence for multiple, independent anion binding sites in the pore. To test for the possible through-space nature of ion-ion interactions inside the CFTR pore, we investigated the interaction between impermeant anions applied to either end of the pore. We found that inclusion of low concentrations of impermeant Pt(NO2) 4 2- ions in the extracellular solution weaken the blocking effects of three different intracellular blockers [Pt(NO2) 4 2- , glibenclamide and 5-nitro-2-(3-phenylpropylamino)benzoic acid] without affecting their apparent voltage dependence. However, the effects of extracellular Pt(NO2) 4 2- ions are too strong to be accounted for by simple competitive models of ion binding inside the pore. In addition, extracellular Fe(CN) 6 3- ions, which do not appear to enter the pore, also weaken the blocking effects of intracellular Pt(NO2) 4 2- ions. In contrast to previous models that invoked interactions between anions bound concurrently inside the pore, we propose that Pt(NO2) 4 2- and Fe(CN) 6 3- binding to an extracellularly accessible site outside of the channel permeation pathway alters the structure of an intracellular anion binding site, leading to weakened binding of intracellular blocking ions.
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U2 - 10.1007/s00232-005-7028-2
DO - 10.1007/s00232-005-7028-2
M3 - Article
C2 - 16794779
AN - SCOPUS:33745894984
SN - 0022-2631
VL - 210
SP - 31
EP - 42
JO - Journal of Membrane Biology
JF - Journal of Membrane Biology
IS - 1
ER -