Table 1

Agonist binding constants (K i) and ligand-independent (IB) and agonist-dependent (IA) coupling efficacy of human WT and mutant B1 and B2 receptors in HEK293 cells

WT B11.67 ± 0.27UB1982058
 B1Stop3462.90 ± 0.90UB1141580
 B1Stop3372.28 ± 0.72UB108840
 B1Stop3285.70 ± 1.15UB55320
 B1Stop3223.24 (2)UB11320
 B1Stop3212.15 (2)UB48404
 B1Stop3204.02 ± 0.24UB23425
 B1R318 0.194 ± 0.031UB198908
WT B2UB1.86 ± 0.340194
 B2Stop321UB2.05 ± 0.60020
 B2Stop320UB1.06 ± 0.750251
 B2Stop314UB1.79 ± 0.2800
 B2Stop313UB3.37 ± 0.7702
 B2A311 UB1.09 ± 0.11221256
 B2A314 0579
 B2A324 0392
 B2A329 0244
 B2Stop313A311 041 (2)
 B2Stop321A311 UB1.09 ± 0.11034 (2)
 B2Stop315A314 2265 (2)
B1(B2ICIV)2.53 ± 0.234337
 B1(B2ICIV)Stop320A317 15108 (2)
 B1(B2ICIV)Stop320A318 43562
 B1(B2ICIVASer/Thr)4.04 ± 0.2440834
 B1(B2ICIVASer/Thr)A346 122982

K i values were obtained from competition binding experiments on intact HEK293 cells expressing each receptor construct and calculated using the Radlig curve-fitting program. The values are presented as the average ± S.E. of at least three experiments or the average of two experiments as indicated after the value. IAand IB values are the slopes from experiments in which cellular PI hydrolysis (dpm) in the absence and presence of agonist was determined as a function of the receptor number (fmol/106cells) as described in Fig. 1. Values were generated with points from at least three different experiments, or two experiments as indicated after the value, with each experiment yielding at least five points and with each point done in duplicate.

    • UB, undetectable binding of the radioligand to the construct.