Cell-signaling assays

A method of identifying a compound as a modulator of G-protein-linked receptor activity that generates or consumes a cyclic nucleotide through the action of a cyclase or phosphodiesterase, comprising:

• conducting a G-protein-linked-receptor mediated reaction that generates or consumes a cyclic nucleotide in the presence of a candidate compound;
• contacting, in vitro, a product of the reaction with a luminescent tracer and with the opposite member of a specific binding pair to the cyclic nucleotide, wherein the tracer and the cyclic nucleotide compete for binding to the opposite member of the specific binding pair;
• illuminating the tracer with polarized light, wherein the light is capable of inducing emission of polarized light from the tracer;
• detecting the extent of polarization of light emitted from the tracer;
• and
• identifying the candidate compound as a modulator of the reaction based on the extent of polarization of the emitted light.