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Voltage‐dependent flickery block of an open cystic fibrosis transmembrane conductance regulator (CFTR) channel pore
Author(s) -
Zhou Zhen,
Hu Shenghui,
Hwang TzyhChang
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0435f.x
Subject(s) - cystic fibrosis transmembrane conductance regulator , chemistry , membrane potential , conductance , hyperpolarization (physics) , patch clamp , biophysics , reversal potential , permeability (electromagnetism) , membrane , biochemistry , stereochemistry , physics , biology , receptor , nuclear magnetic resonance spectroscopy , gene , condensed matter physics
1 Fast flickery block of the cystic fibrosis transmembrane conductance regulator (CFTR) was studied with cell‐attached and whole‐cell patch‐clamp recordings from mouse NIH3T3 cells stably expressing a mutant CFTR channel, K1250A‐CFTR. This mutant CFTR channel, once open, can stay open for minutes. Within a prolonged opening, the kinetics of fast flickery closures can be readily quantified. 2 Flickering block of K1250A‐CFTR channels was voltage dependent since the open probability within an opening burst decreased as the membrane was hyperpolarized. 3 Mean open time (τ o ) and mean closed time (τ c ), obtained from single‐channel kinetic analysis, were corrected for missed events. Our data show that corrected τ c was voltage dependent while corrected τ o exhibited little voltage dependence. Results from whole‐cell current relaxation upon voltage jump further indicate that τ c at a membrane potential of ‐100 mV was at least 10‐fold longer than that at +100 mV. 4 τ c , but not τ o , was sensitive to external permeant anions. After complete replacement of external Cl − with impermeant anions, τ c showed little voltage dependence and approximated a value observed under strong hyperpolarization in the presence of high external permeant anions. These results suggest that the resident time of the blocker is prolonged by conditions (i.e. hyperpolarization or the absence of external permeant anions) that deplete Cl − in the CFTR pore. 5 Results from macroscopic current noise analysis of both wild‐type CFTR and K1250A‐CFTR channels further confirm the voltage dependence and Cl − sensitivity of the fast flickery block observed with single‐channel analysis. 6 We conclude that the voltage dependence of the flickery block in CFTR is mainly due to the voltage‐dependent occupancy of an anion‐binding site in the channel pore by trans‐anions. The blocker acquires a voltage‐dependent off rate through an electrostatic interaction with Cl − in the pore.