Expression in mammalian cells and electrophysiological characterization of two mutant Kv1.1 channels causing episodic ataxia type 1 (EA-1).
Episodic ataxia type 1 (EA-1) is a rare neurological disorder and was the first ionic channel disease to be associated with defects in a potassium channel. Until now 10 different point mutations in the KCNA1-gene have been reported to cause this disorder. We have investigated the functional consequences of two mutations leading to amino acid substitutions in the first and sixth transmembrane segments of a Kv1.1 channel subunit, by means of the patch-clamp technique; we injected cRNA coding for, respectively, F184C and V408A mutant Kv1.1 channels into mammalian cells and compared the resulting currents with those in the wild-type. The expression levels of F184C and V408A mutant channels relative to that of the wild-type was 38 and 68%, respectively. Since the single-channel conductance of the F184C mutant was similar to that of the wild-type (12 pS) without an apparent change in the maximum open probability, we conclude that the lower expression level in the F184C mutant channels is due to a reduced number of functional channels on the cell surface. F184C activated slower, and at more depolarized potentials, and deactivated faster compared with the wild-type. V408A channels deactivated and inactivated faster compared with the wild-type. Studies with different extracellular cations and tetraethylammonium gave no indication that the pore structure was changed in the mutant channels. Acetazolamide, that is helpful in some patients suffering from EA-1, was without effect on Kv1.1 wild-type or mutant channels. This study confirms and extends earlier studies on the functional consequences of Kv1.1 mutations associated with EA-1, in an attempt to understand the pathophysiology of the disease.
Bretschneider
F
F
Department of Applied Physiology, University of Ulm, Germany.
Wrisch
A
A
Lehmann-Horn
F
F
Grissmer
S
S
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001259:Ataxia / Q000235:genetics*; D004553:Electric Conductivity; D004594:Electrophysiology; D051662:Kv1.1 Potassium Channel; D009154:Mutation / Q000502:physiology*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D019789:Tetraethylammonium / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051662:Kv1.1 Potassium Channel; D019789:Tetraethylammonium; D000086:Acetazolamide