Functional modulation of brain sodium channels by cAMP-dependent phosphorylation

Abstract

Voltage-gated Na⁺ channels, which are responsible for the generation of action potentials in brain, are phosphorylated by CAMP-dependent protein kinase in vitro and in intact neurons. Phosphorylation by CAMP-dependent protein kinase reduces peak Na⁺ currents 40%–50% in membrane patches excised from rat brain neurons or from CHO cells expressing type IIA Na⁺ channels. Inhibition of basal cAMP-dependent protein kinase activity by transfection with a plasmid encoding a dominant negative mutant regulatory subunit increases Na⁺ channel number and activity, indicating that even the basal level of kinase activity is sufficient to reduce Na⁺ channel activity significantly. Na+currents in membrane patches from kinase-deficient cells were reduced up to 80% by phosphorylation by cAMP-dependent protein kinase. These effects could be blocked by a specific peptide inhibitor of CAMP-dependent protein kinase and reversed by phosphoprotein phosphatases. Convergent modulation of brain Na⁺ channels by neurotransmitters acting through the CAMP and protein kinase C signaling pathways may result in associative regulation of electrical activity by different synaptic inputs.