To determine the optimal concentration of the mu-opioid agonist (see Note 1), it is often necessary to asses its effect across a range of the doses. This is especially true when characterizing a newly identified receptor isoform or working with variable tissues and cell types. An in-depth discussion of the construction of concentration curves is beyond the scope of the present paper as excellent reviews on this topic already exist (32). A simple way to prepare a dose response curve for morphine to assay cAMP levels in vitro is provided (see Note 2).
