Histamine H1 receptor occupancy triggers inositol phosphates and intracellular calcium mobilization in human non-pigmented ciliary epithelial cells.
Agonists and antagonists of histamine were used to characterize the stimulation of inositol phosphates formation and elevation of intracellular Ca2+ by histamine in cultured non-pigmented epithelial (NPE) cells from human ciliary body. Agonists specific for the H1 histamine receptor subtype were 20- to 200-fold more potent than the H2-specific agonists tested, and 5-16% as potent as histamine in inositol phosphates stimulation. An H1 antagonist was 10,000-fold more potent than an H2 antagonist in blocking histamine stimulation of inositol phosphates. H1 agonists also mimicked and H1 antagonists inhibited the elevation of intracellular Ca2+ by histamine. The first phase of the Ca2+ response to histamine was largely independent of extracellular Ca2+ while the second phase required extracellular Ca2+. Dose-response curves for histamine elevation of intracellular Ca2+ (EC50 = 10 microM, maximum at 100 microM) and inositol phosphates (EC50 = 2 microM, maximum at 100 microM) were similar. These data support the characterization of the NPE histamine receptor as an H1 receptor linked to elevation of inositol phosphates and intracellular Ca2+.
Crook
R B
RB
Cellular Pharmacology Laboratory, University of California, San Francisco 94143-0730.
Bazan
N G
NG
Polansky
J R
JR
D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002852:Chromatography, Ion Exchange; D002924:Ciliary Body / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005470:Fluorometry; D006632:Histamine / Q000494:pharmacology; D006633:Histamine Antagonists / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D011969:Receptors, Histamine H1 / Q000378:metabolism*
D006633:Histamine Antagonists; D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D007295:Inositol Phosphates; D011969:Receptors, Histamine H1; D006632:Histamine; D002118:Calcium