Characterization of Ligand-Binding Properties and Selectivities of Three Rat Tachykinin Receptors by Transfection and Functional Expression of Their Cloned cDNAs in Mammalian Cells1

We investigated the ligand-binding properties and selectivities of rat substance P, substance K and neuromedin K receptors by transfection and functional expressions of the cDNAs for these receptor subtypes in monkey kidney COS cells. Selective radi-oligand binding analysis of both substance P and substance K receptors revealed the presence of high-affinity and low-affinity components which are governed primarily by the difference in rates of dissociation of the ligand-receptor complex. The two affinity components were interconvertible by the presence and absence of a guanine nucleotide, suggesting the involvement of a G protein in the two affinity states. The Iigand bindings of the three receptors were inhibited in different potencies by naturally occurring tachykinins and a series of carboxyl-terminal fragments containing a common tachykinin sequence, and this comprehen