title: Ca(2+)/calmodulin-mediated regulation of the desensitizing process in G(q) protein-coupled histamine H(1) receptor-mediated Ca(2+) responses in human U373 MG astrocytoma cells.
abstract: We investigated Ca(2+)/calmodulin (CaM)-mediated regulation of the desensitizing process of the histamine H(1) receptor-mediated increase in intracellular Ca(2+) concentration in human U373 MG astrocytoma cells. The desensitizing process was evaluated by measuring the histamine-induced Ca(2+) responses in cells pretreated with histamine for 15 s-30 min under various conditions. Under normal physiological conditions, desensitization developed with three successive phases : a fast desensitization within 15 s, a transient resensitization at 45 s, and a prompt and sustained redesensitization from 1 to 30 min. Similar processes of desensitization/resensitization occurred even under hypertonic conditions, where histamine-mediated internalization of the histamine H(1) receptor is inhibited. The transient resensitization phase was selectively prevented by deprivation of extracellular Ca(2+) and, even more strikingly, by the presence of W-7 (a CaM antagonist). FK506 and cyclosporin A, Ca(2+)/CaM-dependent protein phosphatase (PP2B) inhibitors, mimicked such effects. In the presence of KN-62, a Ca(2+)/CaM-dependent protein kinase II (CaM kinase II) inhibitor, the early development of desensitization disappeared, allowing a slow and simple development of desensitization. The early processes of desensitization and resensitization were unaffected by W-5, okadaic acid, and KN-04 (less potent inhibitors against CaM, PP2B, and CaM kinase II, respectively) or by GF109203X and chelerythrine (protein kinase C inhibitors). The high-affinity site for histamine was converted to a lower-affinity site by histamine treatment, which also showed a transient restoration phase at 45 s in a manner sensitive to KN-62 and FK506. These results provide the first evidence that Ca(2+)/CaM plays a crucial role in determining the early phase of the desensitizing process via activation of CaM kinase II and PP2B, by regulating agonist affinity for histamine H(1) receptors.
authors.affiliation: Department of Pharmacodynamics, Meiji Pharmaceutical University, Tokyo, Japan. hishi@mypharm.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Hishinuma
authors.forename: K
authors.initials: K
authors.lastname: Ogura
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D001254:Astrocytoma; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000502:physiology*; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology*; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D019319:Okadaic Acid / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011738:Pyrilamine / Q000494:pharmacology; D011899:Ranitidine / Q000494:pharmacology; D011969:Receptors, Histamine H1 / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology*; D016559:Tacrolimus / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D065095:Calcineurin Inhibitors; D002147:Calmodulin; D004791:Enzyme Inhibitors; D006634:Histamine H1 Antagonists; D010880:Piperidines; D011969:Receptors, Histamine H1; D013449:Sulfonamides; D019319:Okadaic Acid; C063302:KN 62; C017967:W 7; D006632:Histamine; D016572:Cyclosporine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011899:Ranitidine; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D011738:Pyrilamine; C052075:thioperamide; D002118:Calcium; D016559:Tacrolimus