Sequestration of G-Protein bg Subunits by Different G-Protein a Subunits Blocks Voltage-Dependent Modulation of Ca Channels in Rat Sympathetic Neurons
نویسندگان
چکیده
The membrane-delimited and voltage-dependent inhibition of N-type Ca channels is mediated by Gbg subunits. Previously, exogenous excess GDP-bound GaoA has been shown to dramatically attenuate the norepinephrine (NE)-mediated Ca current inhibition by sequestration of Gbg subunits in rat superior cervical ganglion (SCG) neurons. In the present study, we determined whether the attenuation of NE-mediated modulation is specific to GaoA or shared by a number of closely related (Gatr , GaoB, Gai1 , Gai2 , Gai3 , Gaz ) or unrelated (Gas , Gaq , Ga11 , Ga16 , Ga12 , Ga13 ) Ga subunits. Individual Ga subunits from different subfamilies were transiently overexpressed in SCG neurons by intranuclear injection of mammalian expression vectors encoding the desired protein. Strikingly, all Ga subunits except Gaz nearly blocked basal facilitation and NEmediated modulation. Likewise, VIP-mediated Ca current inhibition, which is mediated by cholera toxin-sensitive G-protein, was also completely suppressed by a number of Ga subunits overexpressed in neurons. Gas expression produced either enhancement or attenuation of the VIP-mediated modulation—an effect that seemed to depend on the expression level. The onset of the nonhydrolyzable GTP analog, guanylylimidodiphosphate-mediated facilitation was significantly delayed by overexpression of different GDP-bound Ga subunits. Taken together, these data suggest that a wide variety of Ga subunits are capable of forming heterotrimers with endogenous Gbg subunits mediating voltage-dependent Ca channel inhibition. In conclusion, coupling specificity in signal transduction is unlikely to arise as a result of restricted Ga/Gbg interaction.
منابع مشابه
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