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Mechanisms for the time‐dependent decay of inward currents through cloned Kir2.1 channels expressed in Xenopus oocytes
Author(s) -
Shieh RuChi
Publication year - 2000
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.1469-7793.2000.00241.x
Subject(s) - xenopus , hyperpolarization (physics) , biophysics , chemistry , inward rectifier potassium ion channel , patch clamp , membrane potential , ion , ion channel , stereochemistry , biochemistry , biology , receptor , organic chemistry , nuclear magnetic resonance spectroscopy , gene
1 The decay of inward currents was characterized using the giant patch‐clamp technique in the cloned inward rectifier K + channels Kir2.1 expressed in Xenopus laevis oocytes. 2 The degree of decay was increased by strong hyperpolarization and reduced by increases in external [K + ]. This voltage (membrane potential, V m )‐ and K + ‐dependent decay is referred to as inactivation. The dissociation constant for the protective effects of external K + ions against inactivation was about 5 m m and was not V m dependent. 3 Internal K + ions also showed mildly protective effects against inactivation when external K + sites were not saturated. Results from variations in [K + ] suggest that the hyperpolarization‐induced inactivation of the Kir2.1 channels is not dependent on the driving force for K + ions. 4 In the mutant which demonstrates higher external K + affinity, the degree of inactivation was reduced. These results suggest that binding of K + ions in the external channel pore mouth stabilizes channel opening. 5 Internal Mg 2+ and polyamines induced time‐dependent decay of inward currents in a dose‐dependent but V m ‐independent manner between ‐150 and ‐60 mV. The order of potency for Mg 2+ ‐ and polyamine‐induced decay was different from that for inward rectification. Furthermore, mutations with reduced inward rectification did not show parallel reduction of Mg 2+ ‐ and polyamine‐induced decay. These results suggest that the effects of internal Mg 2+ and polyamines on Kir2.1 channels involve different binding sites. 6 This study provides evidence for V m ‐dependent processes controlling the inactivation of the Kir2.1 channels.