The Slack and Slick genes encode Na+-activated K+ channels, which regulate the rate at which neurons adapt to maintained synaptic stimulation and the accuracy of timing of neuronal action potentials. These channels have also been proposed to play a key role in the protection of neurons and cardiomyocytes from hypoxic injury. In their general structure, they resemble other voltage-gated K channels, but have very large (>600 amino acid) intracellular C-termini. The C-terminal domain of Slack interacts with Fragile- X Mental Retardation protein (FMRP), an RNA-binding protein that regulates trafficking and translation of a subset of subset of neuronal mRNAs. The work in this application will use biochemical and electrophysiological assays to determine the specific regions of Slack and FMRP involved in their interactions both in vitro and in vivo, and will determine which specific regions are required for FMRP to control the gating of Slack channels. We shall also determine how the expression of Na+-activated K+ channels is altered in a mouse model of Fragile X syndrome (Fmr1-/-). In particular we shall determine the mechanism that in Fmr1-/- animals causes the total loss of expression of the distal C- terminus of Slack, a region that appears to be required for FMRP binding to the channels. Parallel electrophysiological and pharmacological experiments will evaluate the effects of this altered pattern of Slack expression on the functional properties of Na+- activated K+ channels in native neurons. An understanding of the biological properties and regulation of Slack and Slick channels will lead to a clearer understanding of the deficits in Fragile X syndrome and related disorders and is expected to lead to the development of novel therapeutic strategies.
Recent evidence suggests that activation of a relatively newly discovered class of proteins, termed sodium- activated potassium channels is regulated by their binding to Fragile X Mental Retardation Protein (FMRP). Inherited loss or deficits in FMRP are the leading cause of inherited intellectual disorders. The experiments in this application will determine the mechanisms and biological consequences of this channel-FMRP interaction. This information will be used to evaluate whether these channels are likely to be therapeutically useful drug targets, and in particular, whether pharmacological manipulations of sodium-activated potassium channels can overcome some of the impairments in neuronal activity that accompany loss of FMRP.
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