title: All-or-none activation of CRAC channels by agonist elicits graded responses in populations of mast cells.
abstract: In nonexcitable cells, receptor stimulation evokes Ca(2+) release from the endoplasmic reticulum stores followed by Ca(2+) influx through store-operated Ca(2+) channels in the plasma membrane. In mast cells, store-operated entry is mediated via Ca(2+) release-activated Ca(2+) (CRAC) channels. In this study, we find that stimulation of muscarinic receptors in cultured mast cells results in Ca(2+)-dependent activation of protein kinase Calpha and the mitogen activated protein kinases ERK1/2 and this is required for the subsequent stimulation of the enzymes Ca(2+)-dependent phospholipase A(2) and 5-lipoxygenase, generating the intracellular messenger arachidonic acid and the proinflammatory intercellular messenger leukotriene C(4). In cell population studies, ERK activation, arachidonic acid release, and leukotriene C(4) secretion were all graded with stimulus intensity. However, at a single cell level, Ca(2+) influx was related to agonist concentration in an essentially all-or-none manner. This paradox of all-or-none CRAC channel activation in single cells with graded responses in cell populations was resolved by the finding that increasing agonist concentration recruited more mast cells but each cell responded by generating all-or-none Ca(2+) influx. These findings were extended to acutely isolated rat peritoneal mast cells where muscarinic or P2Y receptor stimulation evoked all-or-none activation of Ca(2+)entry but graded responses in cell populations. Our results identify a novel way for grading responses to agonists in immune cells and highlight the importance of CRAC channels as a key pharmacological target to control mast cell activation.
authors.affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
authors.forename: Wei-Chiao
authors.initials: WC
authors.lastname: Chang
authors.forename: Joseph
authors.initials: J
authors.lastname: Di Capite
authors.forename: Charmaine
authors.initials: C
authors.lastname: Nelson
authors.forename: Anant B
authors.initials: AB
authors.lastname: Parekh
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000378:metabolism* / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002217:Carbachol / Q000494:pharmacology*; D002413:Cations, Divalent / Q000378:metabolism; D045744:Cell Line, Tumor; D018679:Cholinergic Agonists / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D005260:Female; D054513:Group IV Phospholipases A2 / Q000096:biosynthesis / Q000378:metabolism; D017997:Leukotriene C4 / Q000096:biosynthesis / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology; D008407:Mast Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000378:metabolism / Q000502:physiology
chemical_list: D015220:Calcium Channels; D002413:Cations, Divalent; D018679:Cholinergic Agonists; D011976:Receptors, Muscarinic; D017997:Leukotriene C4; D002217:Carbachol; D048049:Extracellular Signal-Regulated MAP Kinases; D054513:Group IV Phospholipases A2; D002118:Calcium