Tight agonist binding may prevent the correct interpretation of agonist competition binding curves for alpha sub(2)-adrenergic receptors

alpha sub(2)-Adrenergic receptors in calf retina membranes can be specifically labeled with the tritiated antagonist super(3)H-RX 781094. Saturation binding occurs to a single class of noncooperative sites. The findings are confirmed by kinetic experiments using the radiolabeled agonist super(3)H-UK 14304. Slow agonist dissociating kinetics may prevent the correct evaluation of the agonist binding parameters by computerized analysis of competition binding curves when the incubation time is too short, especially at low temperature.