title: Mechanism of the dynorphin-induced dualistic effect on free intracellular Ca2+ concentration in cultured rat spinal neurons.
abstract: In order to study the different mechanisms of dynorphin spinal analgesia and neurotoxicity at low and high doses, the effects of various concentrations of dynorphin A-(1-17) on the free intracellular Ca2+ concentration ([Ca2+]i) in the cultured rat spinal neurons were studied using single cell microspectrofluorimetry. While dynorphin A-(1-17) 0.1-100 microM had no significant effect on basal [Ca2+]i, dynorphin A-(1-17) 0.1 and 1 microM significantly decreased the high KCl-evoked peak [Ca2+]i by 94% and 83% respectively. Dynorphin A-(1-17) 10 and 100 microM did not affect the peak [Ca2+]i following K+ depolarization, but in all these neurons there was a sustained and irreversible rise in [Ca2+]i following high-K+ challenge. Pretreatment with the specific kappa-opioid receptor antagonist nor-binaltorphimine 10 microM, but not the competitive NMDA receptor antagonist, DL-2-amino-5-phosphonovalerate (APV) 10 microM, significantly blocked the inhibitory effect of dynorphin A-(1-17) 0.1 microM on peak [Ca2+]i. However, APV 10 microM and nor-binaltorphimine 10 microM significantly antagonized the sustained rise in [Ca2+]i induced by a high concentration of dynorphin A-(1-17) 10 microM. Furthermore, in the presence, and following the addition, of increasing concentrations of dynorphin A-(1-17) (0.1, 1, 10 and 100 microM), the high concentrations of dynorphin A-(1-17) failed to produce a sustained rise in peak [Ca2+]i. These results suggested that dynorphin exerted a dualistic modulatory effect on [Ca2+]i in cultured rat spinal neurons, inducing a sustained and irreversible intracellular Ca2+ overload via activation of both NMDA and kappa-opioid receptors at higher concentrations, but inhibiting depolarization-evoked Ca2+ influx via kappa-opioid but not NMDA receptors at lower concentrations. Serial addition of graded concentrations of dynorphin A-(1-17) prevented the effect of high concentrations of dynorphin A-(1-17) on [Ca2+]i.
authors.affiliation: Research Institute of Surgery, The Third Military Medical University, Daping, Chongqing, PR China. jshaw@public.cq.sc.cn
authors.forename: W H
authors.initials: WH
authors.lastname: Hu
authors.forename: C H
authors.initials: CH
authors.lastname: Zhang
authors.forename: H F
authors.initials: HF
authors.lastname: Yang
authors.forename: Y F
authors.initials: YF
authors.lastname: Zheng
authors.forename: N
authors.initials: N
authors.lastname: Liu
authors.forename: X J
authors.initials: XJ
authors.lastname: Sun
authors.forename: J
authors.initials: J
authors.lastname: Jen
authors.forename: M F
authors.initials: MF
authors.lastname: Jen
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004399:Dynorphins / Q000494:pharmacology*; D007202:Indicators and Reagents; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
chemical_list: D007202:Indicators and Reagents; D012996:Solutions; D004399:Dynorphins; D011188:Potassium; D002118:Calcium