ABSTRACT
The process of desensitization has been observed in a diverse range of biological systems, including chemotaxis responses of bacteria, pheromone responses of yeast and the adaptation of the eyes to light. The role of desensitization of adrenoceptor-mediated functional responses appears to be to limit the tissue responsiveness during continued neuronal firing or maintained circulating catecholamine levels. This process will thereby protect the tissues from excessive stimulation. The extremely short process of desensitization which involves uncoupling of the receptor from G protein activation occurs within seconds to minutes and may be a further means of turning off the agonist signal. Considerably more work has been done to elucidate the mechanisms of desensitization by use of the ß-adrenoceptor-adenylyl cyclase system because the structure of this receptor and its second messenger coupling has been well denned by molecular biological techniques. Cholinergic responses also display supersensitivity.
