CHARACTERIZATION OF A TACHYKININ PEPTIDE NK2 RECEPTOR TRANSFECTED INTO MURINE FIBROBLAST B82 CELLS

Membranes isolated from a murine fibroblast B82 cell line (SKLKB82#3) transfected with the bovine stomach cDNA pSKR56S exhibited binding of [His(I-125)1]neurokinin A (I-125-NKA) to a single population of sites with a B(max) of 147 fmol/mg of protein and a K(d) of 0.59 nM. Control cell lines had little or no specific binding. The ligand binding in SKLKB82#3 cells was reversible and was inhibited by peptides in the potency rank of neuropeptide-gamma > neuropeptide K > neurokinin A > [10-norleucine]neurokinin A-(4-10) > substance P >> senktide (succinyl-Asp-Phe-MePhe-Gly-Leu-Met-NH2). Specific binding was enhanced by Mn2+, Mg2+, and Ca2+ and was inhibited by guanine nucleotide analogues. Thus, SKLKB82#3 cells have been transfected with NK2 receptors that have become associated with an endogenous guanine nucleotide-binding protein. In comparison with membranes from the hamster urinary bladder, a tissue enriched in NK2 receptors, NK2 receptor antagonists displayed markedly different potencies, either more or less potent, in inhibiting specific binding in membranes of the transfected cells. Furthermore, inhibition of I-125-NKA binding by nucleotide analogues was markedly different in SKLKB82#3 cells compared with hamster bladder tissue. The different binding profile in the cells is not due to an artefact introduced during cDNA transfection because a similar profile was also observed in bovine stomach membranes. These results may indicate the existence of two distinct NK2 receptors.