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Identification and characterization of histamine H 1 ‐ and H 2 ‐receptors in guinea‐pig left atrial membranes by [ 3 H]‐mepyramine and [ 3 H]‐tiotidine binding
Author(s) -
Hattori Yuichi,
Endou Masayuki,
Gando Satoshi,
Kanno Morio
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.tb09829.x
Subject(s) - mepyramine , dissociation constant , histamine , binding site , stereochemistry , histamine h1 receptor , histamine receptor , population , chemistry , receptor , antagonist , guinea pig , biology , biochemistry , endocrinology , demography , sociology
1 Histamine receptors in the membranes prepared from guinea‐pig left atria were characterized with [ 3 H]‐mepyramine and [ 3 H]‐tiotidine binding. 2 The binding of the H 1 ‐antagonist, [ 3 H]‐mepyramine, was saturable and of high affinity with a maximum binding capacity of 307 ± 27 fmol mg −1 protein ( n = 14) and with an equilibrium dissociation constant ( K D ) of 1.5 ± 0.2 n m ( n = 14). The binding was rapid and readily reversible. 3 The competition curve for [ 3 H]‐mepyramine binding by histamine was biphasic and revealed high and low affinity states of binding. The addition of 5′‐guanylylimidodiphosphate (GppNHp) (100 μm) converted this heterogeneous binding into homogeneous binding of low affinity. 4 The competition curves of H 1 ‐antagonists with [ 3 H]‐mepyramine had Hill coefficients not significantly different from unity, consistent with competition with [ 3 H]‐mepyramine at a single site. GppNHp did not shift the competition curves. 5 Dissociation constants for H 1 ‐antagonists determined from inhibition of [ 3 H]‐mepyramine binding correlated well with the constants derived from inhibition of the positive inotropic response of guinea‐pig left atria to histamine. 6 The H 2 ‐antagonist, [ 3 H]‐tiotidine, labelled an apparently homogeneous population of recognition sites with a maximum binding capacity of 41 ± 8 fmol mg −1 protein ( n = 6) and a K D of 10.8 ± 1.2 n m ( n = 6). 7 Although histamine competed for [ 3 H]‐tiotidine binding in a concentration‐dependent manner, the curve was monophasic and was not shifted by GppNHp. 8 It is concluded that both H 1 and H 2 ‐receptors exist in guinea‐pig left atria. H 1 ‐receptors probably couple to intracellular effector(s) through a guanine nucleotide‐dependent transducing mechanism. On the other hand, H 2 ‐receptors seem unlikely to be linked to guanine nucleotide regulatory proteins in guinea‐pig left atria, which may explain the failure of histamine to cause an increase in cyclic AMP in spite of the presence of H 2 ‐receptors.