Antagonist affinities on CGRP receptors. a, apparent pA₂ values for CGRP_8–37 on human cells and tissues. For CGRP receptors (CLR/RAMP1), data have been combined from studies on recombinant receptors and also SK-N-MC cells. b, apparent pA₂ values for BIBN4096BS on rat (▵) and human (•) cells and tissues. It should be noted that because BIBN4096BS is probably an allosteric antagonist (Hay et al., 2006), the apparent pA₂ values are simply to give a guide as to its affinity at the preparations illustrated here. Data for both figures from Hay et al. (2004), updated to 2008 (Sheykhzade et al., 2004; Springer et al., 2004; Kawase et al., 2005; Nodin et al., 2005; Verheggen et al., 2005; Bailey and Hay, 2006; Gupta et al., 2006a,b; Takhshid et al., 2006; Edvinsson et al., 2007; De Mey et al., 2008; Wunder et al., 2008). In addition, an apparent pA₂ for BIBN4096BS of 14 on human pial arteries has been reported (Moreno et al., 2002). Where no error bar is shown, the result is from a single study; otherwise n = 2 to 12. HUVEC, human umbilical vein endothelial cells.