Biomaterial Database

Labelling of Ri adenosine receptors in rat fat cell membranes with (-)-[125iodo]N6-hydroxyphenylisopropyladenosine. 1984

D Ukena, and R Furler, and M J Lohse, and G Engel, and U Schwabe

A new adenosine analogue, (-)-iodo-N6-phydroxyphenylisopropyladenosine [(-)-IHPIA], has been developed for radioligand binding studies of Ri adenosine receptors. In addition, the effects of (-)IHPIA on adenosine-mediated responses of rat fat cells have been characterized. (-)IHPIA is slightly less potent at Ri adenosine receptors than (-)N6-phenylisopropyladenosine [(-)PIA] as assessed by adenylate cyclase and lipolysis studies. (-)IHPIA inhibited basal adenylate cyclase activity with an IC50 of 60 nmol/l compared to an IC50 of 16.3 nmol/l for (-)PIA. (-)PIA and (-)IHPIA inhibited adenosine deaminase-stimulated lipolysis of intact rat fat cells with an IC50 of 0.55 and 3.6 nmol/l. The potency of (-)N6-phydroxyphenylisopropyladenosine [(-)HPIA] was intermediate. (-)HPIA has been labelled with carrier-free Na[125I] to very high specific activity (2,175 Ci/mmol) and used as agonist radioligand in binding studies of Ri adenosine receptors. The binding of (-)[125I]HPIA was saturable, reversible and stereospecific. Saturation analysis revealed two affinity states with dissociation constants (KD) of 0.7 and 7.6 nmol/l and maximal number of binding sites (Bmax) of 0.94 and 0.95 pmol/mg protein. The rate constant of association, k1, was 3.7 X 10(8) l X mol-1 X min-1. Binding was slowly reversible with a t1/2 of 88 min. In competition experiments specific binding was most potently inhibited by (-)PIA, N6-cyclohexyladenosine (CHA), (-)HPIA and (-)IHPIA, followed by 5'-N-ethylcarboxamidoadenosine (NECA) and 2-chloroadenosine. 1,3-Diethyl-8-phenylxanthine (DPX) and 8-phenyltheophylline were the most potent adenosine antagonists with Ki-values of 67 and 83 nmol/l, whereas the methylxanthines 3-isobutyl-1-methylxanthine, theophylline and caffeine had Ki-values between 1 and 21 mumol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D007457	Iodine Radioisotopes	Unstable isotopes of iodine that decay or disintegrate emitting radiation. I atoms with atomic weights 117-139, except I 127, are radioactive iodine isotopes.	Radioisotopes, Iodine
D008066	Lipolysis	The metabolic process of breaking down LIPIDS to release FREE FATTY ACIDS, the major oxidative fuel for the body. Lipolysis may involve dietary lipids in the DIGESTIVE TRACT, circulating lipids in the BLOOD, and stored lipids in the ADIPOSE TISSUE or the LIVER. A number of enzymes are involved in such lipid hydrolysis, such as LIPASE and LIPOPROTEIN LIPASE from various tissues.	Lipolyses
D010660	Phenylisopropyladenosine	N-Isopropyl-N-phenyl-adenosine. Antilipemic agent. Synonym: TH 162.	Isopropylphenyladenosine,L-Phenylisopropyladenosine,N(6)-Phenylisopropyl-Adenosine,L Phenylisopropyladenosine
D011869	Radioligand Assay	Quantitative determination of receptor (binding) proteins in body fluids or tissue using radioactively labeled binding reagents (e.g., antibodies, intracellular receptors, plasma binders).	Protein-Binding Radioassay,Radioreceptor Assay,Assay, Radioligand,Assay, Radioreceptor,Assays, Radioligand,Assays, Radioreceptor,Protein Binding Radioassay,Protein-Binding Radioassays,Radioassay, Protein-Binding,Radioassays, Protein-Binding,Radioligand Assays,Radioreceptor Assays
D011956	Receptors, Cell Surface	Cell surface proteins that bind signalling molecules external to the cell with high affinity and convert this extracellular event into one or more intracellular signals that alter the behavior of the target cell (From Alberts, Molecular Biology of the Cell, 2nd ed, pp693-5). Cell surface receptors, unlike enzymes, do not chemically alter their ligands.	Cell Surface Receptor,Cell Surface Receptors,Hormone Receptors, Cell Surface,Receptors, Endogenous Substances,Cell Surface Hormone Receptors,Endogenous Substances Receptors,Receptor, Cell Surface,Surface Receptor, Cell
D011983	Receptors, Purinergic	Cell surface proteins that bind PURINES with high affinity and trigger intracellular changes which influence the behavior of cells. The best characterized classes of purinergic receptors in mammals are the P1 receptors, which prefer ADENOSINE, and the P2 receptors, which prefer ATP or ADP.	Methyladenine Receptors,Purine Receptors,Purinergic Receptor,Purinergic Receptors,Purinoceptors,Purine Receptor,Purinoceptor,Receptors, Methyladenine,Receptors, Purine,Receptor, Purine,Receptor, Purinergic
D002462	Cell Membrane	The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.	Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D000241	Adenosine	A nucleoside that is composed of ADENINE and D-RIBOSE. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.	Adenocard,Adenoscan
D000262	Adenylyl Cyclases	Enzymes of the lyase class that catalyze the formation of CYCLIC AMP and pyrophosphate from ATP.	Adenyl Cyclase,Adenylate Cyclase,3',5'-cyclic AMP Synthetase,Adenylyl Cyclase,3',5' cyclic AMP Synthetase,AMP Synthetase, 3',5'-cyclic,Cyclase, Adenyl,Cyclase, Adenylate,Cyclase, Adenylyl,Cyclases, Adenylyl,Synthetase, 3',5'-cyclic AMP
D000273	Adipose Tissue	Specialized connective tissue composed of fat cells (ADIPOCYTES). It is the site of stored FATS, usually in the form of TRIGLYCERIDES. In mammals, there are two types of adipose tissue, the WHITE FAT and the BROWN FAT. Their relative distributions vary in different species with most adipose tissue being white.	Fatty Tissue,Body Fat,Fat Pad,Fat Pads,Pad, Fat,Pads, Fat,Tissue, Adipose,Tissue, Fatty