Episodic ataxia type 2 (EA2) is an inherited autosomal dominant disorder related to
cerebellar dysfunction and is associated with mutations in the pore-forming alpha(1A)-subunits of human P/Q-type Ca(2+) channels (
Cav2.1 channels). The majority of EA2 mutations result in significant loss-of-function phenotypes. Whether EA2 mutants may display dominant-negative effects in human, however, remains controversial. To address this issue, five EA2 mutants in the long
isoform of human alpha(1A)-subunits were expressed in Xenopus oocytes to explore their potential dominant-negative effects. Upon coexpressing the
cRNA of alpha(1A)-WT with each alpha(1A)-mutant in molar ratios ranging from 1:1 to 1:10, the amplitude of
Ba(2+) currents through wild-type (WT)-Cav2.1 channels decreased significantly as the relative molar ratio of alpha(1A)-mutants increased, suggesting the presence of an alpha(1A)-mutant-specific suppression effect. When we coexpressed alpha(1A)-WT with
proteins not known to interact with
Cav2.1 channels, we observed no significant suppression effects. Furthermore, increasing the amount of auxiliary subunits resulted in partial reversal of the suppression effects in nonsense but not missense EA2 mutants. On the other hand, when we repeated the same coinjection experiments of alpha(1A)-WT and mutant using a splice variant of alpha(1A)-subunit that contained a considerably shorter COOH terminus (i.e., the short
isoform), no significant dominant-negative effects were noted until we enhanced the relative molar ratio to 1:10. Altogether, these results indicate that for human WT-Cav2.1 channels comprising the long-alpha(1A)-subunit
isoform, both missense and nonsense EA2 mutants indeed display prominent dominant-negative effects.