Figure 2.

Expression and function of β₁-adrenergic receptors in transgenic animals. (A) Detection of β-adrenergic receptors in left ventricular myocardial membranes prepared from wild-type mice (WT) and mice from the two transgenic lines β₁TG7 and β₁TG4. β-Adrenergic receptors were quantified by saturation with the radioligand [¹²⁵I]cyanopindolol. The data shown are means ± SEM of four experiments. (B) Frequency responses in organ bath experiments. Right atria from 8- to 12-week-old wild-type mice (▫) and mice from the two transgenic lines β₁TG7 (▪) and β₁TG4 (●) were mounted in an organ bath. Spontaneous contraction frequencies were recorded under basal conditions and in the presence of increasing concentrations of (−)isoproterenol. EC₅₀ values were 1.5 ± 0.2 nM for wild-type mice, 1.1 ± 0.1 nM for β₁TG7, and 0.4 ± 0.05 nM for β₁TG4, and maximal effects were 233 ± 9, 253 ± 4, and 270 ± 8 beats per min, respectively. The data shown are means ± SEM of nine (WT), six (β₁TG7), and four (β₁TG4) atria.