Modulation of Slack and Slick Channels by Protein Phosphorylation

Leonard K. Kaczmarek, Departments of Pharmacology and Cellular and Molecular Physiology, Yale University

Potassium channels that are activated by intracellular Na+ (KNa channels) are expressed at high levels in many brain regions, including the amygdala and the striatum, suggesting that their activity regulates the firing patterns of neurons in reward/addition pathways. These channels regulate the rate at which neuronal firing adapts to maintained stimulation. KNa channels are encoded by two genes, Slack and Slick. In addition to being regulated by changes in intracellular Na+, both Slack and Slick channels are very strongly modulated by the activation of protein kinase C, and this enzyme represents the most potent mechanism currently known to regulate these channels. Activation of protein kinase C increases Slack currents and slows their rate of activation. In contrast to Slack channels, the activity of Slick channels, as well as of Slack/Slick heteromeric channels, is strongly suppressed upon activation of protein kinase C. A variety of experiment approaches have indicated that the substrate sites that modulate channel activity are likely to be on the very large cytoplasmic C-terminal domains of the channel subunits themselves. These same C-terminal domains have been shown to interact with proteins that regulate local protein translation in neurons, suggesting that phosphorylation of the C-terminal domains may regulate the interaction of these proteins with components of the local protein synthetic machinery. Experiments in this project will use the Discovery Proteomics Core of the Center to identify the specific amino acid residues at which the Slack and Slick channels are phosphorylated under both basal conditions and after activation of protein kinase C. Combined with electrophysiological and molecular biological approaches, this information will lead to an understanding of the contribution of these channels to neuronal firing patterns and to the modulation of synaptic transmission.