Temperature dependence of the binding of [3H]mepyramine and related compounds to the histamine H1 receptor.
The extent of the promethazine-sensitive binding of [3H]mepyramine to a washed fraction from guinea pig cerebellum was little altered between 4 degrees and 30 degrees. The dissociation of [3H]mepyramine from the H1 receptor was markedly temperature-sensitive. An Arrhenius plot of the variation of the dissociation rate constant, k-1, with temperature was linear over the range 37 degrees -15 degrees (E alpha = 160 kJ mole-1). The association rate constant, k1, was also temperature-dependent, and an Arrhenius plot approximated well to a straight line between 30 degrees and 15 degrees (E alpha = 112 kJ mole-1). The linear relationship may hold down to 4 degrees. A consequence of the slow dissociation at 4 degrees is that the IC50 for mepyramine inhibition of promethazine-sensitive [3H]mepyramine binding at 4 degrees is independent of the concentration of [3H]mepyramine if the cerebellar homogenate is first incubated with the nonradioactive antagonist before addition of the 3H-ligand. Promethazine binding showed a temperature dependence similar to that of mepyramine, and for both antagonists and for chlorpromazine the affinity constant was not greatly increased (equal to or less than a factor of 2) at 4 degrees compared with 30 degrees. Tripelennamine showed a more rapid dissociation at 4 degrees than the other antagonists. Mequitazine dissociated slowly at 4 degrees, but the affinity constant was lower at 4 degrees than at 30 degrees.
D000631:Aminopyridines / Q000378:metabolism*; D000818:Animals; D002531:Cerebellum / Q000378:metabolism; D002746:Chlorpromazine / Q000378:metabolism; D006168:Guinea Pigs; D006634:Histamine H1 Antagonists / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010640:Phenothiazines / Q000378:metabolism; D011398:Promethazine / Q000378:metabolism; D011738:Pyrilamine / Q000378:metabolism*; D011968:Receptors, Histamine / Q000378:metabolism*; D011969:Receptors, Histamine H1 / Q000378:metabolism*; D013696:Temperature; D014309:Tripelennamine / Q000378:metabolism
D000631:Aminopyridines; D006634:Histamine H1 Antagonists; D010640:Phenothiazines; D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D014309:Tripelennamine; D011398:Promethazine; D011738:Pyrilamine; D002746:Chlorpromazine; C006069:mequitazine