title: Alpha 2-adrenoceptor-GTP binding regulatory protein-adenylate cyclase system in cerebral cortical membranes of adult and senescent rats.
abstract: The characterization of [3H]clonidine binding and effects of GTP, forskolin, islet-activating protein (IAP) and cholera toxin on adenylate cyclase activity were investigated in cerebral cortical membranes from 70-day-old and 2-year-old rats. Neither Kd nor Bmax values in [3H]clonidine binding were changed between day 70 and year 2. The activation of adenylate cyclase by forskolin was significantly higher in senescent than in adult animals. The inhibitory effect of adrenaline, which was completely abolished by the pretreatment with IAP/NAD on forskolin/GTP-stimulated cyclase activity, was low in senescent rats compared to that in adult ones. The stimulatory effect of cholera toxin/NAD was also low at the senescent stage compared to that at the adult stage. It is suggested that ligand binding affinity and the density in alpha 2-adrenoceptors do not change between day 70 and year 2 but that GTP binding and/or coupling activity of inhibitory as well as stimulatory GTP binding regulatory protein to catalytic units decrease in synaptic membranes of 2-year-old compared to those of 70-day-old rat brain.
mesh_terms: D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism / Q000502:physiology*; D000375:Aging; D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D003000:Clonidine / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000201:enzymology / Q000378:metabolism; D009243:NAD / Q000494:pharmacology; D037342:Pertussis Toxin; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D011942:Receptors, Adrenergic, alpha; D010566:Virulence Factors, Bordetella; D009243:NAD; D005576:Colforsin; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D003000:Clonidine; D004837:Epinephrine