Coupling of M3 acetylcholine receptor to Gq16 activates a natriuretic peptide receptor guanylyl cyclase

Muscarinic activation of tracheal smooth muscle (TSM) involves a M(3)AChR/heterotrimeric-G protein/NPR-GC coupling mechanism. G protein activators Mastoparan (MAS) and Mastoparan-7 stimulated 4- and 10-fold the NPR-GC respectively, being insensitive to PTX and antibodies against Galpha(i/o) subfamily. Muscarinic and MAS stimulation of NPR-GC was blocked by antibodies against C-terminal of Galpha(q16), whose expression was confirmed by RT-PCR. However, synthetic peptides from C-terminal of Galpha(q15/16) stimulated the NPR-GC. Coupling of alpha(q16) to M(3)AChR is supported by MAS decreased [(3)H]QNB binding, being abolished after M(3)AChR-4-DAMP-alkylation. Anti-i(3)M(3)AChR antibodies blocked the muscarinic activation of NPR-GC, and synthetic peptide from i(3)M(3)AChR (M(3)P) was more potent than MAS increasing GTPgamma [(35)S] and decreasing the [(3)H]QNB activities. Coupling between NPR-GC and Galpha(q16) was evaluated by using trypsin-solubilized-fraction from TSM membranes, which displayed a MAS-sensitive-NPR-GC activity, being immunoprecipitated with anti-Galpha(q16), also showing an immunoreactive heterotrimeric-G-beta-subunit. These data support the existence of a novel transducing cascade, involving Galpha(q16)beta gamma coupling M(3)AChR to NPR-GC.