TABLE 1.

Affinities of NMB and Bn for wild-type GRP and NMB receptors on N-terminal truncated NMBR [NMBR(1,40–390)], chimeric GRP, and NMB receptors

The affinities (IC₅₀) were measured by competitive displacement of 50 pM ¹²⁵I-[Tyr⁴]Bn by NMB or Bn in whole-cell radioligand binding assays as described under Materials and Methods. The top part of this table shows the comparison between WT NMBR, N-terminal truncated NMBR, [NMBR(1,40–390)], and stably transfected Balb-3T3 cells and are determined from the dose-inhibition curves shown in Fig. 1. The bottom part of this table shows the IC₅₀ of NMB and Bn for wild-type GRPR, NMBR, four chimeric GRP receptors (gain-of-affinity for NMB), and four chimeric NMB receptors (loss-of-affinity for NMB) transiently expressed in Balb-3T3 cells. The chimeric NMBR and GRPR receptor were made by exchanging the extracellular domain of each receptor as shown in Figs. 2 and 3 and described in their legends. The significant decrease or increase in affinity from the wild type was calculated using the paired t test. Values are mean ± S.E.M. from at least four experiments, and in each experiment, each point was measured in duplicate.

	IC50
	NMB	Bn
	nM
Stably transfected
WT NMBR	0.3 ± 0.1	1.5 ± 0.2
[NMBR(1,40–390)]	0.3 ± 0.1	2.8 ± 0.1
Transiently transfected
WT GRPR	115.1 ± 7.3	0.8 ± 0.1
WT NMBR	1.0 ± 0.2	4.5 ± 0.5
Chimeric GRPRs (gain-of-affinity for NMB)
[e1NMBR]GRPR	61.1 ± 16.3a	0.9 ± 0.3
[e2NMBR]GRPR	128.2 ± 39.5	0.7 ± 0.1
[e3NMBR]GRPR	24.9 ± 4.9b	0.6 ± 0.1
[e4NMBR]GRPR	62.8 ± 15.8a	1.4 ± 0.2
Chimeric NMBRs (loss-of-affinity for NMB
[e1GRPR]NMBR	1.5 ± 0.2	4.0 ± 0.8
[e2GRPR]NMBR	4.0 ± 1.1	4.0 ± 0.7
[e3GRPR]NMBR	80.4 ± 14.5c	5.2 ± 0.7
[e4GRPR]NMBR	2.8 ± 0.5	1.2 ± 0.2

^aa P < 0.03 vs WT GRPR for NMB.

^bb P < 0.004 vs WT GRPR for NMB.

^cc P < 0.0001 vs WT NMBR for NMB.