Some unique properties of CGP-12177.

CGP-12177, like isoproterenol, has a lower affinity for desensitized receptors. Experiments were performed to study whether this property of CGP-12177 is due to its partial agonist activity or its impermeability for membranes. Reduced binding of [3H]DHA to desensitized receptors at 0 degrees C as well as a reversal of the reduced binding in the presence of digitonin indicate a permeability barrier. A partial agonist effect of CGP-12177 was only found in intact C6 cells and neither in C6 membranes nor in S49 cells. This peculiar effect in intact C6 cells is stereospecific and not due to an inhibition of phosphodiesterases.