The DNA encoding the C140 cell surface receptor has been cloned and sequenced. The availability of this DNA permits the recombinant production of the C140 receptor which can be produced at cell or oocyte surfaces and is useful in assay systems both for the detection of substances which affect its activity, including agonists and antagonists. Further, the elucidation of the structure of the C140 receptor permits the design of agonist and antagonist compounds which are useful in these assays. The availability of the C140 receptor also permits production of antibodies specifically immunoreactive with the receptor per se or with specific regions thereof.