The interaction of U-73122 with the histamine H1 receptor: implications for the use of U-73122 in defining H1 receptor-coupled signalling pathways.
U-73122, an N-aminosteroid homologue of N-ethylmaleimide (NEM), widely used as an inhibitor of phospholipase C, was found to be a potent inhibitor (IC50 5.5+/-0.5 microM) of the binding of [3H]mepyramine to guinea-pig cerebellar membranes. The succinimido analogue, U-73343, also inhibited the binding of [3H]mepyramine (estimated IC50 24+/-1 microM), but NEM was only a weak inhibitor, even at 10 mM. The interaction of U-73122 and U-73343 with the H1 receptor was effectively irreversible, on the time-scale of the experiment. There is no indication that reaction with a receptor thiol residue is involved in the binding of U-73122, since preincubation of membranes with 2 mM NEM did not significantly increase the IC50 for the inhibition of [3H]mepyramine binding by U-73122. We conclude that U-73122 binds to the histamine H1 receptor in the concentration range in which it acts as an inhibitor or PLC. This compromises the use of U-73122 to provide evidence that an H1 agonist action is mediated via PLC. The tight binding of U-73343 to the receptor appears to be primarily a function of the hydrophobic nature of the compound.
Hughes
S A
SA
Department of Pharmacology, University of Cambridge, UK.
Gibson
W J
WJ
Young
J M
JM
D000818:Animals; D001667:Binding, Competitive; D004963:Estrenes / Q000378:metabolism* / Q000494:pharmacology; D005033:Ethylmaleimide / Q000378:metabolism / Q000494:pharmacology; D006168:Guinea Pigs; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism / Q000494:pharmacology; D011738:Pyrilamine / Q000037:antagonists & inhibitors / Q000378:metabolism; D011760:Pyrrolidinones / Q000378:metabolism* / Q000494:pharmacology; D011969:Receptors, Histamine H1 / Q000378:metabolism*; D014316:Tritium; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D004963:Estrenes; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D011969:Receptors, Histamine H1; D014316:Tritium; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C074854:U 73343; D010738:Type C Phospholipases; D011738:Pyrilamine; D005033:Ethylmaleimide