Constitutive Activity and Structural Instability of the Wild‐Type Human H2 Receptor

• Published in: Journal of neurochemistry Vol. 71; no. 2; pp. 799 - 807
• Main Authors: Alewijnse, Astrid E., Smit, Martine J., Hoffmann, Marcel, Verzijl, Dennis, Timmerman, Henk, Leurs, Rob
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.08.1998; Blackwell
• Subjects: Animals; Binding, Competitive - physiology; Biological and medical sciences; Burimamide - pharmacology; Cell receptors; Cell structures and functions; CHO Cells - physiology; Cimetidine - pharmacology; Constitutive activity; Cricetinae; Cyclic AMP - metabolism; Dose-Response Relationship, Drug; Down-Regulation - genetics; Down‐regulation; Famotidine - pharmacology; Fundamental and applied biological sciences. Psychology; Gene Expression - drug effects; Histamine H2 Antagonists - pharmacology; Histamine H2 receptor; Humans; Inverse agonism; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine); Ranitidine - pharmacology; Receptors, Histamine H2 - genetics; Structural instability; Up-Regulation - genetics; Up‐regulation; Human; Regulation(control); Structure activity relation; Inverse agonist; Structural instability; CHO cell line; H2 Histamine receptor; Biological receptor
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.1998.71020799.x

: Stable expression of the human H2 receptor in Chinese hamster ovary cells resulted in an increase in basal cyclic AMP (cAMP) production, which was inhibited by the inverse agonists cimetidine, famotidine, and ranitidine with potencies similar to those found for the rat H2 receptor. Burimamide, a neutral antagonist at the rat H2 receptor, behaved as a weak partial agonist at the human H2 receptor. Burimamide competitively antagonized both the histamine‐induced increase in cAMP and the cimetidine‐induced reduction of the basal cAMP level with apparent KB values that were similar to its H2 receptor affinity. Investigation of the modulation of receptor expression after long‐term drug treatment revealed that at low concentrations histamine induced a significant reduction in H2 receptor expression, whereas at high concentrations receptor expression was slightly increased. The partial agonist burimamide induced, like inverse agonists, an upregulation of the human H2 receptor after prolonged treatment. These findings suggest a structural instability of the constitutively active human H2 receptor in transfected Chinese hamster ovary cells. Occupation of the H2 receptor by any ligand reduces the instability, thus resulting in higher cellular expression levels.