Cell-based assay for functional screening of compounds active at the human endothelin A receptor

We have developed a cell based assay for the functional screening of chemical libraries for novel chemical entities active at the human endothelin A (ET(A)) receptor. The assay is relatively inexpensive, suitable for dealing with large number of samples, and simple to operate; it generates results quickly. We achieved this by expressing the cDNA for the receptor in mammalian cell lines and determining whether coupling to pIA(A) occurred through the quantification of released radiolabeled arachidonic acid (AA) into the culture medium. Significant coupling was observed only when the receptor was expressed in the Chinese hamster ovary (CHO) line DG44. The assay could distinguish between ET(A)r agonists and antagonists, and the IC50 (the concentration that inhibits maximum response by 50%) values obtained were similar to those from other sources of receptor. The ET(B) receptor-selective agonist BQ3020 did not stimulate AA release, indicating that the assay can also discriminate between receptor subtypes.