Fig. 2. Effects of α-2 agonists in α-1A and α-1B fluorometric imaging plate reader assay. Intracellular calcium concentration in HEK293 cells expressing (  A ) bovine α-1A receptors and (  B ) rat α-1B receptors. Clonidine and tizanidine are strong α-1A agonists and partial α-1B agonists, but brimonidine is a weak agonist compared with the α-1 agonist, phenylephrine. Data are a representative experiment in triplicate.