title: κ-Opioid receptor inhibition of calcium oscillations in spinal cord neurons.
abstract: Mouse embryonic spinal cord neurons in culture exhibit spontaneous calcium oscillations from day in vitro (DIV) 6 through DIV 10. Such spontaneous activity in developing spinal cord contributes to maturation of synapses and development of pattern-generating circuits. Here we demonstrate that these calcium oscillations are regulated by κ opioid receptors (KORs). The κ opioid agonist dynorphin (Dyn)-A (1-13) suppressed calcium oscillations in a concentration-dependent manner, and both the nonselective opioid antagonist naloxone and the κ-selective blocker norbinaltorphimine eliminated this effect. The KOR-selective agonist (+)-(5α,7α,8β)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec-8-yl]-benzeneacetamide (U69593) mimicked the effect of Dyn-A (1-13) on calcium oscillations. A κ-specific peptide antagonist, zyklophin, was also able to prevent the suppression of calcium oscillations caused by Dyn-A (1-13). These spontaneous calcium oscillations were blocked by 1 μM tetrodotoxin, indicating that they are action potential-dependent. Although the L-type voltage-gated calcium channel blocker nifedipine did not suppress calcium oscillations, the N-type calcium channel blocker ω-conotoxin inhibited this spontaneous response. Blockers of ionotropic glutamate receptors, 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline and dizocilpine maleate (MK-801), also suppressed calcium oscillations, revealing a dependence on glutamate-mediated signaling. Finally, we have demonstrated expression of KORs in glutamatergic spinal neurons and localization in a presynaptic compartment, consistent with previous reports of KOR-mediated inhibition of glutamate release. The KOR-mediated inhibition of spontaneous calcium oscillations may therefore be a consequence of presynaptic inhibition of glutamate release.
authors.affiliation: Department of Pharmacology, Creighton University, Omaha, NE, USA.
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Kelamangalath
authors.forename: Shashank M
authors.initials: SM
authors.lastname: Dravid
authors.forename: Joju
authors.initials: J
authors.lastname: George
authors.forename: Jane V
authors.initials: JV
authors.lastname: Aldrich
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Murray
mesh_terms: D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D017473:Receptors, Opioid, kappa / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism*
chemical_list: D017473:Receptors, Opioid, kappa; D002118:Calcium