title: Characterization of agonist radioligand interactions with porcine atrial A1 adenosine receptors.
abstract: The agonist radioligand (-)-N6-[125I]-p-hydroxyphenylisopropyl-adenosine ([ 125I]HPIA) was used to characterize adenosine recognition sites in porcine atrial membranes. [125I]HPIA showed saturable binding to an apparently homogeneous population of sites with a maximum binding capacity of 35 +/- 3 fmol/mg of protein and an equilibrium dissociation constant of 2.5 +/- 0.4 nM. Kinetic experiments were performed to address the molecular mechanism of [125I]HPIA binding in porcine atrial membranes. [125I]HPIA apparently interacts with the cardiac adenosine receptor in a simple bimolecular reaction. A kinetically derived [125I] HPIA dissociation constant (2.4 nM) was in good agreement with that parameter measured at equilibrium. Guanyl nucleotides negatively modulated [125I]HPIA binding by increasing its rate of dissociation. This finding is consonant with the formation of a ternary complex in porcine atrial membranes, consisting of ligand, receptor, and guanyl nucleotide-binding protein. Prototypic adenosine receptor agonists and antagonists inhibited specific binding in a manner consistent with the labeling of an A1 adenosine receptor. The results of these experiments suggest that the adenosine receptor present in porcine atrial membranes, as labeled by [125I]HPIA, is of the A1 subtype.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives*; D000818:Animals; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D009206:Myocardium / Q000032:analysis*; D010660:Phenylisopropyladenosine / Q000031:analogs & derivatives* / Q000378:metabolism; D011869:Radioligand Assay; D011983:Receptors, Purinergic / Q000032:analysis* / Q000187:drug effects; D013552:Swine; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D007457:Iodine Radioisotopes; D011983:Receptors, Purinergic; D013873:Thionucleotides; D010660:Phenylisopropyladenosine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C036265:N-(4-hydroxyphenyl)-1-isopropyladenosine; D006160:Guanosine Triphosphate; D000241:Adenosine