Collision coupling in the GABA_B receptor–G protein–GIRK signaling cascade

Abstract

The signaling cascade comprising the 4‐aminobutyrate(B) receptor (GABABR), G protein and the G protein‐gated K+ channel (GIRK) mediates neuronal inhibition in the brain. Precoupling between components of the pathway (within a permanent macromolecular complex) has been proposed, but this remains debatable. We investigated this mechanism in Xenopus oocytes by varying the expression of the GABABR. Increased expression of GABABR accelerates activation of GIRK by agonist, implying that some of the components in this cascade interact by a classical collision mechanism. We also find that GABABR has a bidirectional effect on the basal activity of the GIRK channel. Our results suggest a complex mechanism of coupling between GABABR and GIRK which involves elements of both precoupling and collision coupling.

A Collision Coupling Model Governs the Activation of Neuronal GIRK1/2 Channels by Muscarinic-2 Receptors

“…Our results show that the increase in the amount of mRNA of M2R per oocyte (i.e., increase in surface density) speeds up the activation of GIRK1/2 ( Figure 1A, red plot-mono-exponential fit from which we extract t act ), with a corresponding decrease in the time constant of activation ( Figure 1B). These results are consistent with those obtained for M2R-G z -GIRK and GABA B R-G i/o -GIRK cascades in this heterologous model (Vorobiov et al, 2000;Kahanovitch et al, 2017).…”

“…In previous publications, we presented evidence for catalytic collision coupling between M2R and Gα z ( Vorobiov et al, 2000 ) and GABA B receptors with endogenous or coexpressed Gα i/o ( Kahanovitch et al, 2017 ) in the GPCR-G protein-GIRK cascade reconstituted in Xenopus oocytes. To examine whether this is also the case for the M2R-G i/o -GIRK cascade, and for the following quantitative description and kinetic modeling of the cascade, we first characterized the mode of M2R-G i/o coupling using our previously developed strategy ( Vorobiov et al, 2000 ).…”

“…According to this model, a single receptor may activate several G-proteins (as in visual system; (Arshavsky et al, 2002)) and, therefore, an increase in the number of receptors is expected to accelerate activation kinetics of I evoked . Indeed, this was observed for several GPCR-GIRK cascades (Vorobiov et al, 2000;Wellner-Kienitz et al, 2000;Hein et al, 2005;Kahanovitch et al, 2017). The second mechanism posits long-lived "preformed" complexes of GPCRs, G-proteins, regulatory proteins (e.g., Regulators of G Protein Signaling; RGS) and GIRKs in various combinations (Huang et al, 1995;Lavine et al, 2002;Fowler et al, 2006;Jaen and Doupnik, 2006;Dupre et al, 2007;Rusinova et al, 2007;Dupre et al, 2009;Nagi and Pineyro, 2014;Tateyama and Kubo, 2018).…”

Nociceptin/Orphanin-FQ Inhibits Gonadotropin-Releasing Hormone Neurons via G-Protein-Gated Inwardly Rectifying Potassium Channels

“…5 A ) and had no effect on its magnitude (Table 3, rows a and h). It is widely agreed that GABA B receptors are mediated by GIRK channels (Kahanovitch et al, 2017), including in GnRH neurons (Zhang et al, 2009). Thus, the effect of TPNQ was tested on the inhibition triggered by the activation of GABA B receptor.…”

“…The sensitivity of the OFQ inhibition to Cs and Ba, but not to TPNQ, naringin, or ML297, indicated a different subunit composition of the GIRK channels associated with ORL1 (Kobayashi et al, 2011) in GnRH cells and suggested the presence of GIRK2 subunits in their GIRK channels. To further test this hypothesis, baclofen, a GABA B agonist, was used to activate GIRK channels (Kahanovitch et al, 2017). Although GABA B can use two-pore domain potassium channels (Bushell et al, 2002; Deng et al, 2009), the literature supports the role of GABA B using inwardly rectifying potassium currents in GnRH neurons (Wagner et al, 1998; Zhang et al, 2009).…”