Reversible and irreversible labeling and autoradiographic localization of the cerebral histamine H2 receptor using [125I]iodinated probes.
Iodoaminopotentidine (I-APT)--i.e., N-[2-(4-amino-3-iodobenzamido)ethyl]-N'-cyano-N''-(3-[3- (1-piperidinylmethyl)phenoxy]propyl)guanidine--represents one of the most potent H2-receptor antagonists known so far. In membranes of guinea pig brain 125I-APT bound reversibly, selectively, and with high affinity (Kd = 0.3 nM) to a homogeneous population of sites unambiguously identified as H2 receptors by inhibition studies conducted with a large panel of antagonists. 125I-APT binding was also inhibited by histamine, and the effect was modulated by a guanyl nucleotide, which is consistent with the association of the H2 receptor with a guanine nucleotide binding regulatory protein. The low nonspecific binding of 125I-APT generated high contrast autoradiographic pictures in brain sections and established the precise distribution of H2 receptors. Their highly heterogeneous distribution and laminated pattern in some areas--e.g., cerebral and hippocampal cortices--suggest their major association with neuronal elements. These localizations were more consistent than those of H1 receptors with the distribution of histaminergic projections, indicating that H2 receptors mediate a larger number of postsynaptic actions of histamine--e.g., in striatum. Colocalizations of H1 and H2 receptors in some areas account for their known synergistic interactions in cAMP formation induced by histamine. The distribution of 125I-APT binding sites did not strictly parallel that of the H2-receptor-linked adenylate cyclase activity, which may reflect heterogeneity among H2 receptors. After UV irradiation and SDS/PAGE analysis, [125I]iodoazidopotentidine (125I-AZPT), a photoaffinity probe derived from 125I-APT, was covalently incorporated in several peptides, among which the labeling of two peptides of 59 and 32 kDa was prevented by H2 antagonists, suggesting that they correspond to H2-receptor binding peptides or proteolysis products of the latter. These probes should be useful for sensitive radioassays, localization, purification, and molecular studies of the H2 receptor, which were previously impracticable.
Ruat
M
M
Unité de Neurobiologie et Pharmacologie (U. 109), l'Institut National de la Santé et de la Recherche, Paris, France.
Traiffort
E
E
Bouthenet
M L
ML
Schwartz
J C
JC
Hirschfeld
J
J
Buschauer
A
A
Schunack
W
W
D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D001386:Azides / Q000138:chemical synthesis / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006146:Guanidines / Q000138:chemical synthesis / Q000378:metabolism*; D006168:Guinea Pigs; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D009928:Organ Specificity; D011970:Receptors, Histamine H2 / Q000378:metabolism*
D000345:Affinity Labels; D001386:Azides; D006146:Guanidines; D007457:Iodine Radioisotopes; D011970:Receptors, Histamine H2; C063279:iodoaminopotentidine; C063280:iodoazidopotentidine