title: The molecular basis for adrenergic desensitization in hamster brown adipose tissue: uncoupling of adenylate cyclase activation.
abstract: A crude membrane fraction was prepared from hamster brown adipose tissue. Extensive washing of the crude membranes was crucial for the appearance of specific beta-adrenergic receptor binding as assessed by (-)-[3H]dihydroalprenolol. Adrenergic agents competed for the specific binding sites with beta 1-specificity. Binding characteristics were very similar to those earlier found in intact cells, supporting our previous finding that a single (non-tumour) mammalian cell may contain as many as 60,000 beta-adrenergic receptors. Desensitization in situ (i.e. chronic norepinephrine stimulation due to cold acclimation) only marginally affected the number of beta 1-receptors and their affinity (Ki) for norepinephrine. Total (fluoride-stimulated) adenylate cyclase increased somewhat, but the Kact for norepinephrine slightly decreased. Thus the ratio Ki/Kact was rather unaffected by cold acclimation. However, the fraction of adenylate cyclase which could be stimulated by norepinephrine decreased drastically. GTP introduced a low-affinity form (for agonist) of the receptor. The form observed in isolated cells must primarily be the high-affinity form. The basis for desensitization must reside in a diminished ability to transfer the signal from the receptor to the cyclase. This change may be molecularly located in the N-protein or in its interaction with the receptor.
mesh_terms: D000064:Acclimatization; D000262:Adenylyl Cyclases / Q000378:metabolism*; D002001:Adipose Tissue, Brown / Q000201:enzymology*; D000320:Adrenergic Fibers / Q000201:enzymology*; D000818:Animals; D003080:Cold Temperature; D006224:Cricetinae; D004082:Dihydroalprenolol / Q000378:metabolism; D004789:Enzyme Activation; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000502:physiology; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008647:Mesocricetus; D013385:Succinate Dehydrogenase / Q000378:metabolism
chemical_list: D004082:Dihydroalprenolol; D006160:Guanosine Triphosphate; D005993:Glycerolphosphate Dehydrogenase; D013385:Succinate Dehydrogenase; D000262:Adenylyl Cyclases