Table 1.

Inhibition of [³⁵S]-GTPγS binding stimulation in HEK-rCRF₁ cell membranes by the peptide antagonist α-helical CRF(9-41) and the non-peptide antagonist antalarmin

Stimulating ligand	Activity	Stimulation	Antagonism by α-helical CRF(9-41)	Antagonism by antalarmin
		EC50 (M) (pEC50)	Kb (M) (pKb)	Kb (M) (pKb)
Sauvagine	Gs	1.68 × 10−11 (10.78±0.05)	4.41 × 10−9 a (8.36±0.09)	9.05 × 10−9 a (8.04±0.04)
	Gi	3.85 × 10−9 (8.41±0.05)	2.86 × 10−9 a (8.54±0.03)	7.95 × 10−9 b ±7.85 × 10−10
Urocortin	Gs	1.11 × 10−11 (10.96±0.06)	1.31 × 10−8 a (7.88±0.10)	8.33 × 10−8 a (7.08±0.09)
	Gi	4.90 × 10−10 (9.31±0.06)	1.04 × 10−8 a (7.98±0.01)	2.85 × 10−8 b ±1.91 × 10−9

The results are from concentration–response curves of sauvagine- and urocortin-evoked binding of [³⁵S]-GTPγS to HEK-rCRF₁ cell membranes at conditions selectively representing activation of Gs- or Gi-proteins in the absence and presence of the antagonists. As shown in Figures 1 and 2, EC₅₀ values for the stimulation by sauvagine and urocortin and K_b values for the antagonists were calculated. The constants and their pK values are presented as means±s.e.

Between sauvagine and urocortin, the Schild pK_b and Gaddum K_b values of antalarmin were significantly different (P<0.001), as were the Schild pK_b values of α-helical CRF(9-41) (P<0.05).

^aSchild analysis for competitive antagonism.

^bGaddum analysis for non-competitive antagonism.