PT  - JOURNAL ARTICLE
AU  - Leid, M
AU  - Schimerlik, M I
AU  - Murray, T F
TI  - Characterization of agonist radioligand interactions with porcine atrial A1 adenosine receptors.
DP  - 1988 Sep 01
TA  - Molecular Pharmacology
PG  - 334--339
VI  - 34
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/34/3/334.short
4100  - http://molpharm.aspetjournals.org/content/34/3/334.full
SO  - Mol Pharmacol1988 Sep 01; 34
AB  - 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.