The affinity of histamine for Gq protein-coupled histamine H(1)-receptors is predominantly regulated by their internalization in human astrocytoma cells.
We examined the regulatory mechanisms of the affinity of Gq protein-coupled histamine H(1)-receptors for histamine after histamine pretreatment in intact human U373 MG astrocytoma cells. In control cells, the displacement curves for histamine against the binding of 5 nM [(3)H]mepyramine, a radioligand for H(1)-receptors, showed the presence of two binding sites for histamine, that is, high and low affinity sites. Pretreatment with 0.1 mM histamine for 30 min at 37°C induced a significant reduction in the percentage of high affinity sites for histamine and a concomitant increase in the percentage of low affinity sites with no change in their pIC(50) values. These histamine-induced changes were insensitive to 30 µM KN-62, an inhibitor of Ca(2+)/calmodulin-dependent protein kinase II, but they were completely inhibited either by 0.4 mM ZnCl(2), an inhibitor of G protein-coupled receptor kinases (GRKs), or under hypertonic conditions, where clathrin-mediated endocytosis is known to be inhibited. These results suggest that histamine-induced conversion of high to low affinity sites for histamine is predominantly regulated by GRK/clathrin-mediated internalization of H(1)-receptors in human astrocytoma cells.
Department of Pharmacodynamics, Meiji Pharmaceutical University, Tokyo 204-8588, Japan. hishi@my-pharm.ac.jp
Shigeru
S
Hishinuma
Yuko
Y
Sato
Chizuru
C
Akatsu
Masaru
M
Shoji
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D001254:Astrocytoma / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D002966:Clathrin / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D054768:G-Protein-Coupled Receptor Kinases / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006632:Histamine / Q000378:metabolism*; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006801:Humans; D011969:Receptors, Histamine H1 / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D017967:Zinc Compounds / Q000494:pharmacology
D002712:Chlorides; D002966:Clathrin; D006634:Histamine H1 Antagonists; D011969:Receptors, Histamine H1; D017967:Zinc Compounds; C063302:KN 62; D006632:Histamine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; C016837:zinc chloride; D054768:G-Protein-Coupled Receptor Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D002118:Calcium