Rat parotid adenylate cyclase and Alpha-amylase secretion desensitize to Beta-adrenergic agonists without any receptor down-regulation. The hypothesis that desensitization of adenylate cyclase activity to Beta-adrenergic agonists in rat parotid is mediated through effects involving the catalytic subunit of adenylate cyclase will be tested.
The specific aims of the proposal are to determine the mechanism(s) by which desensitization is produced and by which forskolin counteracts desensitization. Monoclonal antibodies have been raised to purified adenylate cyclase catalytic subunit (protein obtained from Dr. A. G. Gilman). Desensitized and control adenylate cyclase catalytic subunit will be isolated by specific antibody interaction or by affinity chromatography on forskolin-Sepharose. Metabolic labelling studies will be performed to determine whether desensitization is produced by incorporation of a covalent modification into the catalytic subunit, or if a potential Desensitizing Ligand is responsible. Carbachol produces a stable depression of adenylate cyclase in rat parotid which is pharmacologically similar to isoproterenol-produced desensitization. The mechanism of carbachol effect will likewise be determined. Forskolin counteracts desensitization and stable depression, respectively. Its mechanism of action will be tested similarly. Phorbol esters have been found to produce desensitization symptoms, and their mechanism of doing so will be established. Reconstitution of purified components is the ultimate goal. Rat parotid will be used as a model tissue for understanding post-receptor mechanisms of desensitization. Desensitized Beta-adrenergic response is a major problem in therapy of certain disease states, including asthma. Better understanding of physiological control of salivary secretion will also result from these studies.
| Harper, J F (1988) Stimulus-secretion coupling: second messenger-regulated exocytosis. Adv Second Messenger Phosphoprotein Res 22:193-318 |
