Table 2.

Dissociation constants (K_B values) of antagonist inhibition

Receptor	Drug	Response	Adult, M	Fetus, M
α1	Prazosin (10−8 M)	Contraction	6.4 × 10−10	1.1 × 10−10
		[Ca2+]i	1.1 × 10−10	1.6 × 10−10
α1A	5-MU (10−8 M)	Contraction	1.1 × 10−9	0.2 × 10−9
		[Ca2+]i	1.1 × 10−9	0.7 × 10−9
α1B	CEC (10−5 M)	Contraction	5.3 × 10−10	No significant inhibition
		[Ca2+]i	0.8 × 10−10
α1D	BMY-7378 (10−7 M)	Contraction	6.7 × 10−9	No significant inhibition
		[Ca2+]i	25 × 10−9

[Ca²⁺]_i, intracellular Ca²⁺ concentration. See methods for details.