G-protein-coupled A1 adenosine receptors in coated vesicles of mammalian brain: characterization by radioligand binding and photoaffinity labelling

Abstract:

A 1 adenosine receptors in coated vesicles have been characterized by radioligand binding and photoaffinity labelling. Saturation experiments with the antagonist 8-cyclopentyl-1, 3-[3 H] dipropyl-xanthine ([3 H] DPCPX) gave a K d value of 0.7 nM and a B max value of 82±13 fmol/mg protein. For the highly A 1-selective agonist 2-chloro-N 6-[3 H] cyclopentyladenosine ([3 H] CCPA) a K d value of 1.7 nM and a B max value of 72±29 fmol/mg protein was estimated. Competition of agonists for [3 H] DPCPX binding gave a pharmacological profile with R-N 6-phenylisopropyladenosine (R-PIA)> CCPA> S-PIA> 5′-N-ethylcarboxamido-adenosine (NECA), which is identical to brain membranes. The competition curves were best fitted according to a two-site model, suggesting the existence of two affinity states. GTP shifted the competition curve for CCPA to the right and only one affinity state similar to the low affinity state in …

Año de publicación:

1992

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Fuente:

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