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Department of Microbiology and Molecular Genetics, University of California, Irvine, California 92697-4025
Functional modulation of voltage-gated sodium channels
affects the electrical excitability of neurons. Protein kinase A (PKA) can decrease sodium currents by phosphorylation at consensus sites in
the cytoplasmic I-II linker. Once the sites are phosphorylated, however, additional PKA activity can increase sodium currents by an
unknown mechanism. When the PKA sites were eliminated by substitutions
of alanine for serine, peak sodium current amplitudes were increased by
20-80% when PKA was activated in Xenopus oocytes either
by stimulation of a coexpressed
2-adrenergic receptor or
by perfusion with reagents that increase cAMP. Potentiation required
the I-II linker of the brain channel, in that a chimeric channel in
which the brain linker was replaced with the comparable linker from the
skeletal muscle channel did not demonstrate potentiation. Using a
series of chimeric and deleted channels, we demonstrate that
potentiation is not dependent on any single region of the linker and
that the extent of potentiation varies depending on the total length
and the residues throughout the linker. These data are consistent with
the hypothesis that potentiation by PKA is an indirect process
involving phosphorylation of an accessory protein that interacts with
the I-II linker of the sodium channel.
modulation; ion channel; phosphorylation; protein kinase A; site-directed mutagenesis
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