PHOSPHORYLATION OF BRAIN SODIUM-CHANNELS IN THE I-II LINKER MODULATESCHANNEL FUNCTION IN XENOPUS OOCYTES

Voltage-gated sodium channels, which initiate action potentials in mam malian brain neurons, are modulated functionally by cAMP-dependent pro tein kinase A (PKA), resulting in reduced sodium current amplitude. Co mparing brain and muscle sodium channels, we show that only the brain channel is modulated by PKA, The brain sodium channel I-II linker is b oth necessary and sufficient for PKA modulation, as shown by exchangin g the I-II linker regions of the two channels, PKA consensus sites in the brain channel I-II linker were eliminated by deletion and site-spe cific mutagenesis. The mutant channels demonstrated decreased levels o f phosphorylation when metabolically labeled in oocytes with [gamma-P- 32]-ATP, and they did not respond with a reduction in current magnitud e after PKA induction, Modulation of the brain channel by PKA phosphor ylation was mimicked by adding fixed negative charges at the PKA conse nsus sites, suggesting that the decrease in current was a direct resul t of the negative charge at one or more of the PKA sites in the I-II l inker.