Gα₁₄ subunit-mediated inhibition of voltage-gated Ca²⁺ and K⁺ channels via neurokinin-1 receptors in rat celiac-superior mesenteric ganglion neurons

The mechanisms by which G proteins modulate voltage-gated Ca²⁺ channel currents (CaV), particularly Ca_V2.2 and CaV2.3, are voltage dependent (VD) or voltage independent (VI). VD pathways are typically mediated by Gα_i/o and Gα_S subfamilies. On the other hand, VI inhibition modulation is coupled to the Gα_q subfamily and signaling pathways downstream of phospholipase C stimulation. In most studies, this latter pathway has been shown to be linked to Gα_q and/or Gα₁₁ protein subunits. However, there are no studies that have examined whether natively expressed Gα₁₄ subunits (Gα_q subfamily member) couple G protein-coupled receptors (GPCR) with Ca_V2.2 channels. We report that Gα₁₄ subunits functionally couple the substance P (SP)/neurokinin-1 (NK-1) receptor pathway to Ca_V2.2 channels in acutely dissociated rat celiac-superior mesenteric ganglion (CSMG) neurons. Exposure of CSMG neurons to SP blocked the Ca_V2.2 currents in a predominantly VD manner that was pertussis toxin and cholera toxin resistant, as well as Gα_q/11 independent. However, silencing Gα₁₄ subunits significantly attenuated the SP-mediated Ca²⁺ current block. In another set of experiments, exposure of CSMG neurons to SP led to the inhibition of KCNQ K⁺ M-currents. The SP-mediated M-current block was significantly reduced in neurons transfected with Gα₁₄ smallinterference RNA. Finally, overexpression of the GTP-bound Gα_q/11 binding protein RGS2 did not alter the block of M-currents by SP but significantly abolished the oxotremorine methiodidemediated M-current inhibition. Taken together, these results provide evidence of a new Gα₁₄-coupled signaling pathway that modulates Ca_V2.2 and M-currents via SP-stimulated NK-1 receptors in CSMG neurons.