Diversity among skeletal muscle fiber types is controlled by innervation-dependent and muscle fiber type specific cell signaling and downstream transcriptional regulation. A cell signaling pathway has been revealed that regulates avian slow myosin heavy chain 2 (MyHC2) gene expression in innervated secondary muscle fibers. This signaling cascade, initiated by innervation-induced depolarization, is mediated by the inositol 1,4,5 triphoshate receptor 1 (IP3R1). Importantly, innervation- induced expression of the slow MyHC2 gene is fiber type specific in that muscle fibers in vitro derived from myoblasts of slow muscle origin are induced to express slow MyHC2, but muscle fibers in vitro derived from myoblasts of fast muscle origin are refractory to slow MyHC2 gene expression. To elucidate the regulatory signaling mechanism governing this cell type specific induction of slow MyHC2 gene expression, we have developed an in vitro electrical stimulation model. Muscle fiber type specific induction of slow MyHC2 gene expression is maintained in this stimulation model allowing us to initiate structure/function analyses of the cell type specific response to cell depolarization, resulting in differential expression of the slow MyHC2 gene. Results of our current studies focus on the differential regulation of IP3R1 activity via fiber type specific protein-protein interactions and the effect of these interactions on muscle fiber type specific gene expression will be discussed.