Coupling of M2 muscarinic receptors to membrane ion channels via phosphoinositide 3-kinase γ and atypical protein kinase C

Abstract

We report a novel signaling pathway linking M2 muscarinic receptors to metabotropic ion channels. Stimulation of heterologously expressed M2 receptors, but not other G(i)/G(o)-associated receptors (M4 or α(2c)), activates a calcium- and voltage-independent chloride current in Xenopus oocytes. We show that the stimulatory pathway linking M2 receptors to these chloride channels consists of Gβγ stimulation of phosphoinositide 3-kinase γ (PI-3Kγ), formation of phosphatidylinositol 3,4,5-trisphosphate (PIP3), and activation of atypical protein kinase C (PKC). The chloride current is activated in the absence of M2 receptor stimulation by the injection of PIP3, and PIPs current activation is blocked by a pseudosubstrate inhibitory peptide of atypical PKC but not other PKCs. Moreover, the current is activated by injection of recombinant PKCζ at concentrations as low as 1 nM. M2 recepto-current coupling was disrupted by inhibiton of PI-3K and by injection of βγ binding peptides, but it was not affected by expression of dominant negative p85 cRNA. We also show that this pathway mediates M2 receptor coupling to metabotropic nonselective cation channels in mammalian smooth muscle cells, thus demonstrating the broad relevance of this signaling cascade in neurotransmitter signaling.