title: Calcitonin gene-related peptide elevates calcium and polarizes membrane potential in MG-63 cells by both cAMP-independent and -dependent mechanisms.
abstract: Published data suggest that the neuropeptide calcitonin gene-related peptide (CGRP) can stimulate osteoblastic bone formation; however, interest has focused on activation of cAMP-dependent signaling pathways in osteogenic cells without full consideration of the importance of cAMP-independent signaling. We have now examined the effects of CGRP on intracellular Ca(2+) concentration ([Ca(2+)](int)) and membrane potential (E(m)) in preosteoblastic human MG-63 cells by single-cell fluorescent confocal analysis using fluo 4-AM-fura red-AM and bis(1,3-dibarbituric acid)-trimethine oxanol [DiBAC(4)(3)] bis-oxonol assays. CGRP produced a two-stage change in [Ca(2+)](int): a rapid transient peak and a secondary sustained increase. Both responses were dose dependent with an EC(50) of approximately 0.30 nM, and the maximal effect (initially approximately 3-fold over basal levels) was observed at 20 nM. The initial phase was sensitive to inhibition of Ca(2+) mobilization with thapsigargin, whereas the secondary phase was eliminated only by blocking transmembrane Ca(2+) influx with verapamil or inhibiting cAMP-dependent signaling with the Rp isomer of adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS). These data suggest that CGRP initially stimulates Ca(2+) discharge from intracellular stores by a cAMP-independent mechanism and subsequently stimulates Ca(2+) influx through L-type voltage-dependent Ca(2+) channels by a cAMP-dependent mechanism. In addition, CGRP dose-dependently polarized cellular E(m), with maximal effect at 20 nM and an EC(50) of 0.30 nM. This effect was attenuated with charybdotoxin (-20%) or glyburide (glibenclamide; -80%), suggesting that E(m) hyperpolarization is induced by both Ca(2+)-activated and ATP-sensitive K(+) channels. Thus CGRP signals strongly by both cAMP-dependent and cAMP-independent signaling pathways in preosteoblastic human MG-63 cells.
authors.affiliation: Medical Research Service (151), Kansas City Dept. of Veterans Affairs Medical Center, 4801 E. Linwood Blvd., Kansas City, MO 64128, USA. dburns@kumc.edu
authors.forename: Douglas M
authors.initials: DM
authors.lastname: Burns
authors.forename: Lisa
authors.initials: L
authors.lastname: Stehno-Bittel
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Kawase
mesh_terms: D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018613:Microscopy, Confocal; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D012516:Osteosarcoma; D015221:Potassium Channels / Q000378:metabolism; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: D005456:Fluorescent Dyes; D015221:Potassium Channels; D018015:Receptors, Calcitonin Gene-Related Peptide; D000242:Cyclic AMP; D015740:Calcitonin Gene-Related Peptide; D002118:Calcium