Table 1.

Potency (pEC₅₀) and maximal agonist response (E_max) in the presence of the GLP-1 receptor antagonist, exendin-3

[Exendin-3] (M)	cAMP		GPA1/Gαs		GPA1/Gαi
	pEC50a	Emaxb	pEC50a	Emaxb	pEC50a	Emaxb
Vehicle	10.2 ± 0.1***	100 ± 4.3***	7.9 ± 0.1	100 ± 9.0***	7.3 ± 0.07*	100 ± 9.2***
1 ± 10−11	10.1 ± 0.1***	100 ± 5.7***	7.8 ± 0.1	100 ± 9.2***	6.9 ± 0.1*	100 ± 8.1***
1 ± 10−8	9.2 ± 0.1***	61.7 ± 6.2***	7.6 ± 0.2	68 ± 7.1***	6.8 ± 0.2*	81 ± 7.1***
1 ± 10−6	8.9 ± 0.1***	49.5 ± 7.1***	7.3 ± 0.4	23 ± 7.0***	6.7 ± 0.1*	42 ± 5.9***
	cAMP		GPA1/Gαs		GPA1/Gαi
	Slopec	pKBd	Slopec	pKBd	Slopec	pKBd
1 ± 10−8	0.5 ± 0.005	7.9 ± 0.1	0.5 ± 0.006	7.8 ± 0.1	0.13 ± 0.006	7.9 ± 0.1***

Values generated through fitting of a three-parameter logistic equation and represent the mean ± SEM from five independent experimental repeats.

^aThe negative logarithm of the agonist concentration required to generate half the maximal response.

^bThe maximal response to the ligand expressed as a percentage of that obtained in the absence of antagonist.

^cSlope of linear regression from double reciprocal plot of GLP-1 in the presence and absence of 10 nM exendin-3.

^dThe negative logarithm of the equilibrium disassociation constant for the antagonist calculated using the method of Gaddum et al., 1955. Statistical significance compared with vehicle (*P < 0.05, **P < 0.01; ***P < 0.001) was determined by one-way anova with Dunnett's post-test.