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Characterization of diadenosine tetraphosphate (Ap 4 A) binding sites in cultured chromaffin cells: evidence for a P 2y site
Author(s) -
Pintor Jesús,
Torres Magdalena,
Castro Enrique,
MirasPortugal M. Teresa
Publication year - 1991
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1991.tb12363.x
Subject(s) - binding site , stereochemistry , chemistry , receptor , adenosine , chromaffin cell , biology , biochemistry , catecholamine , adrenal medulla , neuroscience
1 Diadenosine tetraphosphate (Ap 4 A) a dinucleotide, which is stored in secretory granules, presents two types of high affinity binding sites in chromaffin cells. A K d value of 8 ± 0.65 × 10 −11 m and B max value of 5420 ± 450 sites per cell were obtained for the high affinity binding site. A K d value of 5.6 ± 0.53 × 10 −9 m and a B max value close to 70,000 sites per cell were obtained for the second binding site with high affinity. 2 The diadenosine polyphosphates, Ap 3 A, Ap 4 A, Ap 5 A and Ap 6 A, displaced [ 3 H]‐Ap 4 A from the two binding sites, the K i values being 1.0 n m , 0.013 n m , 0.013 n m and 0.013 n m for the very high affinity binding site and 0.5 μ m , 0.13 μ m , 0.062 μ m and 0.75 μ m for the second binding site. 3 The ATP analogues displaced [ 3 H]‐Ap 4 A with the potency order of the P 2y receptors, adenosine 5′‐O‐(2 thiodiphosphate) (ADP‐β‐S) > 5′‐adenylyl imidodiphosphate ( AMP‐PNP ) > α,β‐methylene ATP (α,β‐MeATP), in both binding sites. The K i , values were respectively 0.075 n m , 0.2 n m and 0.75 n m for the very high affinity binding site and 0.125 μ m , 0.5 μ m and 0.9 μ m for the second binding site.