A derivative of befunolol, BFE-55, interacts with only the high affinity sites in beta-adrenoceptors

The effect of BFE-55, a derivative of befunolol (a beta-adrenergic partial agonist) on specific [3H]befunolol binding to a microsomal fraction from the guinea pig taenia caecum was tested. A Scatchard plot of specific [3H]befunolol binding in the absence of BFE-55 was concave, suggesting an existence of high and low affinity sites in beta-adrenoceptors. In contrast, the Scatchard plot of data in the presence of BFE-55 (3 X 10(-7) M) was straight. In the presence of BFE-55, the high affinity sites disappeared and the low affinity site was unaffected. In the absence and presence of BFE-55 there was no difference between the pKD values or Bmax values at the low affinity site. These findings indicate that BFE-55 interacts with only the high affinity sites in beta-adrenoceptors.