Premium
A 1 adenosine receptor inhibition of cyclic AMP formation and radioligand binding in the guinea‐pig cerebral cortex
Author(s) -
Alexander Stephen P.H.,
Curtis Alistair R.,
Kendall David A.,
Hill Stephen J.
Publication year - 1994
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.1476-5381.1994.tb17166.x
Subject(s) - ccpa , adenosine , guinea pig , radioligand , agonist , adenosine receptor , adenosine a1 receptor , medicine , chemistry , endocrinology , forskolin , receptor , biology
1 A 1 adenosine receptors were investigated by radioligand binding and functional studies in slices and particulate preparations from guinea‐pig cerebral cortex. 2 Binding of the adenosine receptor antagonist radioligand, 8‐cyclopentyl‐[ 3 H]‐1,3‐dipropylxanthine (DPCPX) to guinea‐pig cerebral cortical membranes exhibited high density (1410 ± 241 fmol mg −1 protein) and high affinity ( K d 3.8 ± 0.3 n m ). 3 [ 3 H]‐DPCPX binding to guinea‐pig cerebral cortical membranes was displaced in a monophasic manner by adenosine receptor antagonists with the rank order of affinity ( K i values, n m ): DPCPX (6) < xanthine amine congener (XAC, 153) < PD 115,199 (308). 4 Agonist displacement of [ 3 H]‐DPCPX binding was biphasic and exhibited the following rank order at the low affinity site ( K i values): 2‐chloro‐N 6 ‐cyclopentyl‐adenosine (CCPA, 513 n m ) = N 6 ‐R‐phenyl‐isopropyladenosine (R‐PIA, 526 n m ) = M 6 ‐cyclopentyladenosine (CPA, 532 n m ) < 2‐chloroadenosine (2CA, 3.2 μ m ) = 5′‐N‐ethylcarboxamidoadenosine (NECA, 4.6 μ m ) < N 6 ‐S‐phenylisopropyladenosine (S‐PIA, 19.9 μ m ). 5 In cerebral cortical slices, [ 3 H]‐DPCPX binding was displaced by antagonists and agonists in an apparently monophasic manner with the rank order of affinity ( K i values, n m ): DPCPX (14) < XAC (45) < R‐PIA (266) < PD 115,199 (666) < S‐PIA (21000). 6 Cyclic AMP accumulation stimulated by 30 μ m forskolin in guinea‐pig cerebral cortical slices was inhibited by R‐PIA, CCPA and CPA up to 1 μ m in a concentration‐dependent fashion with IQo values of 14, 18, and 22 n m , respectively. All three analogues inhibited the forskolin response to a similar extent (82–93% inhibition). NECA, S‐PIA and 2CA failed to inhibit the forskolin response, but rather enhanced the accumulation of cyclic AMP at concentrations of 100 n m or greater, presumably through activation of A 2b adenosine receptors coupled to stimulation of cyclic AMP accumulation in guinea‐pig cerebral cortical slices. 7 The inhibition of forskolin‐stimulated cyclic AMP accumulation by CPA was antagonized with the rank order of affinity ( K i values, n m ): DPCPX (6) < XAC (52) < PD 115,199 (505). 8 Xanthine‐based antagonists inhibited the adenosine receptor augmentation of histamine‐induced phosphoinositide turnover in guinea‐pig cerebral cortical slices with the rank order of affinity ( K i , n m ): DPCPX (12) = XAC (17) < PD 155,199 (640). 9 In summary, we observe a good correlation between antagonist affinity at A 1 receptors defined by radioligand binding, inhibition of cyclic AMP generation or augmentation of histamine‐evoked phosphoinositide turnover in guinea‐pig cerebral cortex.