title: The relationship between beta-adrenoceptor regulation and beta-adrenergic responsiveness in hepatocytes. Studies on acquisition, desensitization and resensitization of isoproterenol-sensitive adenylate cyclase in primary culture.
abstract: The role of beta-adrenoceptor regulation in the mechanisms controlling beta-adrenergic responsiveness in hepatocytes was explored, using primary monolayer cultures. When plated in vitro, these cells gradually acquire a strong catecholamine-sensitive adenylate cyclase activity and an enhanced ability to bind the beta-adrenoceptor ligand [125I]iodocyanopindolol (125ICYP). Examination of the time course showed that the increase in the number of 125ICYP binding sites was detectable within 1-2 h of culturing and slightly preceded the elevation of isoproterenol-responsive activity. Then the responsiveness rose steeply and between about 5-24 h it closely followed the increase in beta-receptor binding. Addition of isoproterenol (10 microM) to cells after 20 h of culturing caused a rapid homologous desensitization of the adenylate cyclase (50% after about 5 min). This was paralleled by a down-regulation of beta-adrenoceptors measured both in membrane particles and in total cell lysates. Removal of isoproterenol led to a resensitization of the adenylate cyclase, which was rapid and protein-synthesis-independent after a brief (10-min) desensitization, or slow and cycloheximide-sensitive after prolonged (4-h) exposure to the agonist. In both cases an up-regulation of the 125ICYP binding paralleled the recovery from refractoriness. In contrast, no concurring changes in 125ICYP binding were measured when the beta-adrenoceptor-linked adenylate cyclase activity was enhanced by pretreatment with pertussin toxin (islet-activating protein, IAP) or was desensitized by exposure of the cells to glucagon or 8-bromo-cAMP; however, these modulations of the adenylate cyclase were nonselective, since the pretreatments with IAP, glucagon or 8-bromo-cAMP affected both isoproterenol-sensitive and glucagon-sensitive activities. The results suggest that, in hepatocytes, regulation at the beta-adrenoceptor level is a major determinant for both short-term and long-term selective changes of the beta-adrenergic responsiveness.
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005934:Glucagon / Q000494:pharmacology; D020120:Iodocyanopindolol; D007545:Isoproterenol / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D037342:Pertussis Toxin; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D011943:Receptors, Adrenergic, beta; D010566:Virulence Factors, Bordetella; D015124:8-Bromo Cyclic Adenosine Monophosphate; D020120:Iodocyanopindolol; D005934:Glucagon; D010869:Pindolol; D037342:Pertussis Toxin; D000262:Adenylyl Cyclases; D007545:Isoproterenol