MECHANISMS OF DESENSITIZATION OF ADRENERGIC RECEPTORS

The objective of the proposed research is to elucidate the molecular
mechanisms involved in desensitization of adrenergic receptors by
catecholamines and other agonists. Previous studies in isolated cells in
culture have documented several distinct steps involved in the overall
process of desensitization; however, the molecular nature of the changes
involved remains unknown. Recent studies indicate the widespread
occurrence and clinical significance of desensitization of adrenergic
receptors in various human tissues, in particular heart, lung, leukocytes,
and lymphocytes. Furthermore, preliminary studies suggest that the
cellular mechanisms involved in desensitization in these tissues in intact
animals are probably similar to those demonstrated in cultured cells. Thus
further studies of the molecular mechanisms involved in desensitization in
cultural cell lines, which are more amenable to study, will likely lead to
information that will be of relevance to understanding desensitization in
various tissues in man. The proposed studies will use recently developed techniques involving
short-time assays with intact cells to study the molecular events involved
in desensitization of beta-adrenergic receptors (BAR). These assays will
further investigate the involvement of internalization of BAR in
desensitization of cultured human astrocytoma cells (1321N1) and will be
used to identify inhbitors of the various biochemical reactions involved in
desensitization. The possible involvement of the cytoskeletal system,
transmethylation reactions, and various ions and ion gradients in
desensitization will be investigated. Other studies will attempt to
develop permeabilized and broken cell systems in which biochemical studies
of receptor modification can be carried out. Finally, the intact cell
binding techniques developed for study of BAR will also be applied to a
study of the likely involvement of similar changes in alpha1-adrenergic
receptors on intact cells in culture.