Vol. 280, Issue 2, 795-801, 1997

Nitrous Oxide Enhances Na⁺/Ca⁺⁺Exchange in the Neuroblastoma Cell Line SK-N-SH¹

M. C. Resendes² , G. C. Kalogeros, S. J. Dixon³ and R. B. Philp

Departments of Pharmacology and Toxicology (M.C.R., G.C.K., R.B.P.) and of Physiology and Division of Oral Biology, Faculty of Dentistry (S.J.D.), The University of Western Ontario, London, Ontario, Canada

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.