The ligand binding signals to a wide variety of seven transmembrane cell surface receptors are transduced into intracellular signals through heterotrimeric G-proteins. Recently, there have been reports which show diverse coupling patterns of ligand-activated receptors to the members of Gq family $alpha$ subunits. In order to shed some light on these complex signal processing networks, interactions between G$alpha$q family of G protein and neurokinin-2 receptor as well as muscarinic M$_{1}$ receptor, which are considered to be new thearpeutic targets in asthma, were studied. Using washed membranes from Cos-7 cells co-transfected with different G.alpha.q and receptor cDNAs, the receptors were stimulated with various concentrations of carbachol and neurokinin A and the agonist-dependent release of [$^3H$]inositol phosphates through phospholipase C beta-1 activation was measured. Differential coupling of Gaq family of G-protein to muscarinic M$_{1}$ receptor and neurokinin-2 receptor was observed. The neurokinin-2 receptor shows a ligand-mediated response in membranes co-transfected with G$alpha$q, G$alpha$11 and G$alpha$14 but not G$alpha$16 and the ability of the muscarinic $M_1$ receptor to activate phospholipase C through G$alpha$/11 but not G$alpha$14 and G$alpha$16 was demonstrated. Clearly G$alpha$/11 can couple $M_1$ and neurokinin-2 receptor to activate phospholipase C. But, there are differences in the relative coupling of the G$alpha$14 and G$alpha$16 subunits to these receptors.