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Differential contribution of two serine residues of wild type and constitutively active β 2 ‐adrenoceptors to the interaction with β 2 ‐selective agonists
Author(s) -
Kikkawa Hideo,
Kurose Hitoshi,
Isogaya Masafumi,
Sato Yoji,
Nagao Taku
Publication year - 1997
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 - 10.1038/sj.bjp.0701229
Subject(s) - isoprenaline , agonist , chemistry , partial agonist , salmeterol , salbutamol , intrinsic activity , terbutaline , practolol , endocrinology , pharmacology , receptor , medicine , stimulation , propranolol , biochemistry , biology , asthma
We have studied the difference in receptor binding activity between partial and full β 2 ‐adrenoceptor agonists and the abilities of the agonists to interact with Ser 204 and Ser 207 in the fifth transmembrane region of the β 2 ‐adrenoceptor, amino acid residues that are important for activation of the β 2 ‐adrenoceptor. In the binding study with [ 125 I]‐iodocyanopindolol, the K i values of (±)‐salbutamol, (±)‐salmeterol, TA‐2005 and (−)‐isoprenaline for the β 2 ‐adrenoceptor expressed in COS‐7 cell membranes were 3340, 21.0, 12.0 and 904n m , respectively. The β 1 /β 2 selectivity of these agonists was in the order of (±)‐salmeterol (332 fold)>TA‐2005 (52.8)>(±)‐salbutamol (6.8)>(−)‐isoprenaline (1.1), and the β 3 ‐/β 2 ‐adrenoceptor selectivity of these agonists was in the order of TA‐2005 (150 fold)>(±)‐salmeterol (88.6)>(±)‐salbutamol (10.4)>(−)‐isoprenaline (3.2). The maximal activation of adenylyl cyclase by stimulation of the β 1 ‐, β 2 ‐ and β 3 ‐adrenoceptors by TA‐2005 was 32, 100 and 100% of that by (−)‐isoprenaline, respectively, indicating that TA‐2005 is a full agonist at the β 2 ‐ and β 3 ‐adrenoceptors and a partial agonist at the β 1 ‐adrenoceptor. (±)‐Salbutamol and (±)‐salmeterol were partial agonists at both β 1 ‐ (8% and 9% of (−)‐isoprenaline) and β 2 ‐ (83% and 74% of (−)‐isoprenaline) adrenoceptors. The affinities of full agonists, TA‐2005 and (−)‐isoprenaline, were markedly decreased by substitution of Ala for Ser 204 (S204A) of the β 2 ‐adrenoceptor, whereas this substitution slightly reduced the affinities of partial agonists, (±)‐salbutamol and (±)‐salmeterol. Although the affinities of full agonists for the S207A‐β 2 ‐adrenoceptor were decreased, those of partial agonists for the S207A‐β 2 ‐adrenoceptor were essentially the same as for the wild type receptor. The constitutively active mutant (L266S, L272A) of the β 2 ‐adrenoceptor had an increased affinity for all four agonists. The affinities of full agonists were decreased by substitution of Ser 204 of the constitutively active mutant, whereas the degree of decrease was smaller than that caused by the substitution of the wild type receptor. Although the affinities of (±)‐salbutamol and (±)‐salmeterol for the S207A‐β 2 ‐adrenoceptor were essentially the same as those for the wild type β 2 ‐adrenoceptor, the affinities of (±)‐salbutamol and (±)‐salmeterol for the constitutively active β 2 ‐adrenoceptor were decreased by substitution of Ser 207 . These results suggest that Ser 204 and Ser 207 of the wild type and constitutively active β 2 ‐adrenoceptors differentially interacted with β 2 ‐selective agonists.