title: Ca2+/calmodulin-mediated regulation of agonist-induced sequestration of Gq protein-coupled histamine H1 receptors in human U373 MG astrocytoma cells.
abstract: We investigated the regulation by intracellular Ca2+ of agonist-induced sequestration of Gq protein-coupled histamine H1 receptors in human U373 MG astrocytoma cells. Histamine-induced sequestration of H1 receptors from the cell surface membrane was detected as the loss of [3H]mepyramine binding sites on intact cells accessible to the hydrophilic H1-receptor antagonist pirdonium. The changes in the pirdonium-sensitive binding of [3H]mepyramine were mirrored by changes in the subcellular distribution of H1 receptors detected by sucrose density gradient centrifugation. The histamine-induced sequestration of H1 receptors did not occur in hypertonic medium, in which clathrin-mediated endocytosis is known to be inhibited, but was significantly accelerated in the absence of extracellular Ca2+ or in the presence of the calmodulin antagonists W-7 and calmidazolium. Inhibitors of protein kinase C (H-7 and GF109203X), Ca2+/calmodulin-dependent protein kinase II (KN-62), or protein phosphatase 2B (FK506) did not alter the time course of H1-receptor sequestration. These results provide the first evidence that agonist-induced, clathrin-mediated sequestration of Gq protein-coupled receptors is transiently inhibited by Ca2+/calmodulin, with the result that receptors remain on the cell surface membrane during the early stage of agonist stimulation.
authors.affiliation: Department of Pharmacodynamics, Meiji Pharmaceutical University, Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Hishinuma
authors.forename: A
authors.initials: A
authors.lastname: Naiki
authors.forename: H
authors.initials: H
authors.lastname: Tsuga
authors.forename: J M
authors.initials: JM
authors.lastname: Young
mesh_terms: D001254:Astrocytoma / Q000378:metabolism / Q000473:pathology; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002147:Calmodulin / Q000502:physiology*; D002499:Centrifugation, Density Gradient; D003470:Culture Media / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology; D017442:Histamine Agonists / Q000494:pharmacology*; D006634:Histamine H1 Antagonists / Q000378:metabolism; D006801:Humans; D006982:Hypertonic Solutions / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011738:Pyrilamine / Q000378:metabolism; D011940:Receptor Aggregation / Q000502:physiology; D011969:Receptors, Histamine H1 / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D014407:Tumor Cells, Cultured
chemical_list: D065095:Calcineurin Inhibitors; D002147:Calmodulin; D003470:Culture Media; D004791:Enzyme Inhibitors; D017442:Histamine Agonists; D006634:Histamine H1 Antagonists; D006982:Hypertonic Solutions; D011969:Receptors, Histamine H1; D006632:Histamine; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D011738:Pyrilamine; D002118:Calcium