Abstract
The agonist radioligand (-)-N6-[125I]-p-hydroxyphenylisopropyladenosine ([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.
Original language | English (US) |
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Pages (from-to) | 334-339 |
Number of pages | 6 |
Journal | Molecular Pharmacology |
Volume | 34 |
Issue number | 3 |
State | Published - 1988 |
Externally published | Yes |
All Science Journal Classification (ASJC) codes
- Molecular Medicine
- Pharmacology