Src Tyrosine Kinases Regulate Neuronal Differentiation of Mouse Embryonic Stem Cells Via Modulation of Voltage-Gated Sodium Channel Activity.

Voltage-gated Na channel activity is vital for the proper function of excitable cells and has been indicated in nervous system development. Meanwhile, the Src family of non-receptor tyrosine kinases (SFKs) has been implicated in the regulation of Na channel activity. The present investigation tests the hypothesis that Src family kinases influence neuronal differentiation via a chronic regulation of Na channel functionality. In cultured mouse embryonic stem (ES) cells undergoing neural induction and terminal neuronal differentiation, SFKs showed distinct stage-specific expression patterns during the differentiation process. ES cell-derived neuronal cells expressed multiple voltage-gated Na channel proteins (Na) and underwent a gradual increase in Na channel activity. While acute inhibition of SFKs using the Src family inhibitor PP2 suppressed the Na current, chronic inhibition of SFKs during early neuronal differentiation of ES cells did not change Na expression. However, a long-lasting block of SFK significantly altered electrophysiological properties of the Na channels, shown as a right shift of the current-voltage relationship of the Na channels, and reduced the amplitude of Na currents recorded in drug-free solutions. Immunocytochemical staining of differentiated cells subjected to the chronic exposure of a SFK inhibitor, or the Na channel blocker tetrodotoxin, showed no changes in the number of NeuN-positive cells; however, both treatments significantly hindered neurite outgrowth. These findings suggest that SFKs not only modulate the Na channel activation acutely, but the tonic activity of SFKs is also critical for normal development of functional Na channels and neuronal differentiation or maturation of ES cells. [ABSTRACT FROM AUTHOR]