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

Abstract

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