title: Identification of three isoforms of the InsP3 receptor in human myometrial smooth muscle.
abstract: The mechanisms responsible for the mobilisation of Ca2+ from intracellular stores sensitive to inositol trisphosphate (InsP3) were studied in saponin-permeabilised human myometrial cells in which the sarcoplasmic reticulum was pre-loaded with 45Ca2+. InsP3-induced 45Ca2+ release was measured over the InsP3 concentration range of 100 nM to 100 microM and showed a graded response. InsP3-induced 45Ca2+ release was inhibited by heparin (20-40 microg/ml) but not significantly affected by caffeine. The Ca2+ sensitivity of InsP3-induced Ca2+ release was measured under conditions which were designed to exclude interference with Ca2+ released by the ryanodine receptor/channel complex. The data showed a bell-shaped relationship with the InsP3 receptor (InsP3R) functional at 10 nM, becoming maximally activated at 300 nM but inhibited at 10 microM Ca2+. Messenger RNA encoding for three isoforms of InsP3R, type I, II and type III, was shown to be present. The relative expression levels of these messengers were obtained by ratio-PCR analysis and the levels of expression of the different isoforms were found to differ between individual patients.
authors.affiliation: Department of Physiological Sciences, The Medical School, The University, Newcastle upon Tyne NE2 4HH, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Morgan
authors.forename: H
authors.initials: H
authors.lastname: De Smedt
authors.forename: J I
authors.initials: JI
authors.lastname: Gillespie
mesh_terms: D001483:Base Sequence; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D015220:Calcium Channels / Q000737:chemistry* / Q000235:genetics; D002478:Cells, Cultured; D005260:Female; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007536:Isomerism; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000737:chemistry* / Q000166:cytology; D009215:Myometrium; D016133:Polymerase Chain Reaction / Q000379:methods; D011247:Pregnancy; D012333:RNA, Messenger / Q000032:analysis; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000235:genetics
chemical_list: D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D002118:Calcium