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Regulation of mammalian Shaker ‐related K + channels: evidence for non‐conducting closed and non‐conducting inactivated states
Author(s) -
Jäger Heike,
Rauer Heiko,
Nguyen Angela N.,
Aiyar Jayashree,
Chandy K. George,
Grissmer Stephan
Publication year - 1998
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.1469-7793.1998.291bw.x
Subject(s) - shaker , histidine , chemistry , tetramer , potassium channel , lysine , asparagine , protonation , stereochemistry , amino acid , biophysics , mutant , leucine , potassium , extracellular , biochemistry , ion , enzyme , biology , organic chemistry , physics , quantum mechanics , gene , vibration
1 Using the whole‐cell recording mode we have characterized two non‐conducting states in mammalian Shaker ‐related voltage‐gated K + channels induced by the removal of extracellular potassium, K + o . 2 In the absence of K + o , current through Kv1.4 was almost completely abolished due to the presence of a charged lysine residue at position 533 at the entrance to the pore. Removal of K + o had a similar effect on current through Kv1.3 when the histidine at the homologous position (H404) was protonated (pH 6.0). Channels containing uncharged residues at the corresponding position (Kv1.1: Y; Kv1.2: V) did not exhibit this behaviour. 3 To characterize the nature of the interaction between Kv1.3 and K + o concentration ([K + ] o ), we replaced H404 with amino acids of different character, size and charge. Substitution of hydrophobic residues (A, V and L) either in all four subunits or in only two subunits in the tetramer made the channel insensitive to the removal of K + o , possibly by stabilizing the channel complex. Replacement of H404 with the charged residue arginine, or the polar residue asparagine, enhanced the sensitivity of the channel to 0 mm K + o , possibly by making the channel unstable in the absence of K + o . Mutation at a neighbouring position (400) had a similar effect. 4 The effect of removing K + o on current amplitude does not seem to be correlated with the rate of C‐type inactivation since the slowly inactivating G380F mutant channel exhibited a similar [K + ] o dependence as the wild‐type Kv1.3 channel. 5 CP‐339,818, a drug that recognizes only the inactivated conformation of Kv1.3, could not block current in the absence of K + o unless the channels were inactivated through depolarizing pulses. 6 We conclude that removal of K + o induces the Kv1.3 channel to transition to a non‐conducting ‘closed’ state which can switch into a non‐conducting ‘inactivated’ state upon depolarization.