title: Nitrous oxide enhances Na+/Ca++ exchange in the neuroblastoma cell line SK-N-SH.
abstract: Changes in the concentration of cytosolic free calcium ([Ca++]i) play fundamental roles in the initiation and regulation of many neuronal processes. Altered regulation of [Ca++]i has been implicated in the action of some anesthetics. We investigated the effects of nitrous oxide (N2O) on Ca++ mobilization and membrane potential in the human neuroblastoma cell line SK-N-SH. [Ca++]i was monitored by fluorescence spectrophotometry of cells loaded with fura-2 or fluo-3. N2O reversibly suppressed carbachol-stimulated increases in [Ca++]i. N2O also inhibited increases in [Ca++]i induced by calcium ionophore or depolarization suggesting a mechanism involving enhanced efflux or sequestration of cytosolic Ca++. The inhibitory effect of N2O was attenuated when the transmembrane Na+ gradient was altered either by suspending cells in nominally Na(+)-free buffer or by pretreating cells with ouabain. The inhibitory effect of N2O was also attenuated by the Na+/Ca++ exchange inhibitor 3,4-dichlorobenzamil. The effects of N2O on membrane potential were measured fluorimetrically using bis(1,3-dibutylthiobarbituric acid)-trimethine oxonol. In the presence of N2O, resting membrane potential was hyperpolarized, a condition that would favor Ca++ efflux mediated by the electrogenic Na+/Ca++ exchanger. Taken together, these findings indicate that N2O suppresses carbachol-stimulated increases in [Ca++]i by enhancing Na+/Ca++ exchange activity. Enhancement of neuronal Na+/Ca++ exchange may contribute to the anesthetic action of N2O.
authors.affiliation: Department of Pharmacology, The University of Western Ontario, London, Canada.
authors.forename: M C
authors.initials: MC
authors.lastname: Resendes
authors.forename: G C
authors.initials: GC
authors.lastname: Kalogeros
authors.forename: S J
authors.initials: SJ
authors.lastname: Dixon
authors.forename: R B
authors.initials: RB
authors.lastname: Philp
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000814:Aniline Compounds; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D002460:Cell Line; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009447:Neuroblastoma; D009609:Nitrous Oxide / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D013050:Spectrometry, Fluorescence; D014407:Tumor Cells, Cultured; D014966:Xanthenes
chemical_list: D000814:Aniline Compounds; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D019831:Sodium-Calcium Exchanger; D014966:Xanthenes; C041470:3',4'-dichlorobenzamil; C059715:Fluo-3; D015759:Ionomycin; D010042:Ouabain; D000584:Amiloride; C056369:5-(N-methyl-N-isobutyl)amiloride; D012964:Sodium; D009609:Nitrous Oxide; D002118:Calcium; D016257:Fura-2