Table 4

Effect of Ca2+ on the affinities of several compounds on the GABABR1a S269A mutant compared with the wild-type receptor

AgonistsIC50 (μM)IC50(μM)IC50/IC50
 GABA238  ± 28227  ± 550.95
 APPA86.0  ± 4.0140  ± 31.63
 Baclofen28.8  ± 5.431.2  ± 0.91.08
AntagonistsIC50 (nM)IC50(nM)IC50/IC50
 CGP642134.48  ± 0.847.04  ± 2.111.57
 CGP54626A102  ± 26123  ± 211.21
 CGP56999A1.43  ± 0.372.77  ± 0.941.93

[125I]CGP64213 binding on membranes prepared from HEK 293 cells expressing the indicated receptor was measured in the absence and presence of increasing concentrations of the indicated compounds. IC50 values were determined as described underExperimental Procedures. Experiments were conducted in the presence of 1 mM Ca2+, or in the presence of 1 mM EGTA with no added Ca2+. Values are means ± S.E.M. of at least three independent experiments performed in triplicate. The ratio of the mean IC50 determined in the absence of Ca2+ over those determined in the presence of Ca2+ is indicated.