Characterization of granulocyte beta adrenergic receptors in atopic eczema

The binding of (-)-3H-dihydroalprenolol (3H-DHA) and 125I-hydroxybenzylpindolol (125I-HYP) to the beta-adrenergic receptors in homogenized granulocyte preparations from control subjects and patients with atopic eczema was characterized. No difference was found for the affinity (KD=2 X 10(-9) M) or the total number of high-affinity binding sites (1,200 to 1,600 per cell) with 3H-DHA or 125I-HYP (KD 1.6 X 10(-10) M) in granulocytes from the two study populations. Scatchard plots of the data obtained from DHA binding isotherms suggested that negative cooperativity may exist as a property of the beta 2-receptor. Granulocyte preparations from control subjects and patients with atopic eczema also showed propranolol protectable 3H-DHA binding with a KD of 10(-7) M. It is not clear whether these 3H-DHA binding sites represent physiologically significant beta-adrenergic receptors at these concentrations of radioligand. It was found that 15,000 to 20,000 binding sites of this lower affinity for DHA exist per cell in granulocytes from the two populations of subjects. These data suggest that the reduced isoproterenol responsiveness of granulocytes from patients with atopic eczema is not the result of abnormal or reduced numbers of beta-adrenergic receptors.