The proposed research will examine the molecular, biophysical and intracellular signaling mechanisms by which insulin-like growth factor-1 (IFG-1) rapidly regulates neuronal L-type calcium channels via activation of its receptor tyrosine kinase (RTK). RTKs are ubiquitously expressed on post-mitotic neurons, but little is known about their neuronal function(s). Our recent studies using cerebellar granule neurons demonstrate that, within seconds of activating the IGF-1/RTK, both N and L calcium channel activities alter dramatically in ways expected to increase neuroexcitability, synaptic release, and somal calcium influx, and that RTK regulation of L channels is a controlling factor in neuronal survival. Here, we will: (1) Determine the regulated sites on the channels through biochemical (mapping phosphorylation sites) and molecular biological approaches (expression of mutated channels in neuronal cell lines), using biophysical analyses to assess whether and how the IGF-1-L channel regulation is modified. (2) Identify the biophysical mechanisms of the RTK-induced modulation by single channel analysis of the cerebellar L channels. (3) Define the intracellular pathway linking the IGF-1/RTK activation to L channel modulation through transient expression of active, inactive, and constitutively active variants of signaling components in granule neurons in culture. Together, the proposed experiments will provide significant insights into the mechanisms that regulate neuroexcitability, with particular relevance to development, damage- and age-induced states of under- activity and epileptic states of over-activity.
