Collision coupling in the GABAB receptor-G protein-GIRK signaling cascade.

The signaling cascade comprising the 4-aminobutyrate(B) receptor (GABAB R), 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 GABAB R. Increased expression of GABAB R 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 GABAB R has a bidirectional effect on the basal activity of the GIRK channel. Our results suggest a complex mechanism of coupling between GABAB R and GIRK which involves elements of both precoupling and collision coupling.