title: Calcium-sensing receptor activation induces intracellular calcium oscillations.
abstract: Parathyroid hormone secretion is exquisitely sensitive to small changes in serum Ca2+ concentration, and these responses are transduced via the Ca2+-sensing receptor (CaR). We utilized heterologous expression in HEK-293 cells to determine the effects of small, physiologically relevant perturbations in extracellular Ca2+ on CaR signaling via phosphatidylinositol-phospholipase C, using changes in fura 2 fluorescence to quantify intracellular Ca2+. Chronic exposure of CaR-transfected cells to Ca2+ in the range from 0.5 to 3 mM modulated the resting intracellular Ca2+ concentration and the subsequent cellular responses to acute extracellular Ca2+ perturbations but had no effect on thapsigargin-sensitive Ca2+ stores. Modest, physiologically relevant increases in extracellular Ca2+ concentration (0.5 mM increments) caused sustained (30-40 min) low-frequency oscillations of intracellular Ca2+ (approximately 45 s peak to peak interval). Oscillations were eliminated by 1 microM thapsigargin but were insensitive to protein kinase inhibitors (staurosporine, KN-93, or bisindolylmaleimide I). Staurosporine did increase the fraction of cells oscillating at a given extracellular Ca2+ concentration. Serum Ca2+ concentrations thus chronically regulate cells expressing CaR, and small perturbations in extracellular Ca2+ alter both resting intracellular Ca2+ as well as Ca2+ dynamics.
authors.affiliation: Department of Physiology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205, USA. gbreitwi@pop.jhmi.edu
authors.forename: G E
authors.initials: GE
authors.lastname: Breitwieser
authors.forename: L
authors.initials: L
authors.lastname: Gama
mesh_terms: D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000166:cytology; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection
chemical_list: D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D047428:Protein Kinase Inhibitors; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D019284:Thapsigargin; D011494:Protein Kinases; D002118:Calcium; D016257:Fura-2