Hormone action at the membrane level. V. Binding of ( [formula omitted])-[ 3H]isoproterenol to intact chicken erythrocytes and erythrocyte ghosts

Abstract

The binding of ( ±)-[7- 3H]isoproterenol to intac chicken erythrocytes has been investigated by a rapid centrifugation technique. The binding is displaceable by a one thousand-fold excess of cold isoproterenol and consists of two fractions, only one of which is inhibitable by the beta antagonist (−)-propranolol. The total displaceable binding to intact cells amounts to 80 or 127 molecules per cell at a( ±)-isoproterenol concentration of 0.4 μM depending on the method employed to analyze the binding. Under similar conditions, the total displaceable binding to isolated membrane ghosts is 12 600 molecules per cell. The propranolol-inhibitable binding to intact cell reaches saturation within 5 min at 4 °C and gives by Scatchard analysis a maximum binding of 108 molecules per cell and with a K D of 0.4 μM. 50% inhibition of binding is obtained with 0.3 μM unlabeled (−)-isoproterenol as compared to 20 μM unlabeled (−)-isoproterenol. The binding of isoproterenol thus shows a marked stereospecific preference for the (−)-isomer.