Expression in mammalian cells and electrophysiological characterization oftwo 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 f irst ionic channel disease to be associated with defects in a potassium cha nnel. Until now 10 different point mutations in the KCNA1-gene have been re ported to cause this disorder. We have investigated the functional conseque nces 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 pa tch-clamp technique; we injected cRNA coding for, respectively, F184C and V 408A mutant Kv1.1 channels into mammalian cells and compared the resulting currents with those in the wild-type. The expression levels of F184C and V4 08A mutant channels relative to that of the wild-type was 38 and 68%, respe ctively. Since the single-channel conductance of the F184C mutant was simil ar to that of the wild-type (12 pS) without an apparent change in the maxim um open probability, we conclude that the lower expression level in the F18 4C 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 deactiva ted and inactivated faster compared with the wild-type. Studies with differ ent extracellular cations and tetraethylammonium gave no indication that th e 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 studi es on the functional consequences of Kv1.1 mutations associated with EA-1, in an attempt to understand the pathophysiology of the disease.