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ANESTHETIC PHARMACOLOGY

Isoflurane Inhibits Cyclic Adenosine Monophosphate Response Element-Binding Protein Phosphorylation and Calmodulin Translocation to the Nucleus of SH-SY5Y Cells

Jin Zhang, MD^*, Jhon-Jairo Sutachan, BS^*, Jose Montoya-Gacharna, MD^*, Chong-Feng Xu, PhD, Fang Xu, PhD^*, Thomas A. Neubert, PhD, Esperanza Recio-Pinto, PhD^*, and Thomas J. J. Blanck, MD, PhD^*

From the *Department of Anesthesiology, Kimmel Center for Biology and Medicine at the Skirball Institute, and Departments of Pharmacology, and Physiology and Neuroscience, NYU School of Medicine, New York City, New York.

Address correspondence and reprint requests to Thomas J. J. Blanck, Department of Anesthesiology, RR607A, NYU School of Medicine, 550 1st Ave., New York, NY 10016. Address e-mail to thomas.blanck{at}nyumc.org.

BACKGROUND: Calmodulin (CaM) activation by Ca²⁺, its translocation to the nucleus, and stimulation of phosphorylation of cyclic adenosine monophosphate response element-binding protein (CREB) (P-CREB) are necessary for new gene expression and have been linked to long-term potentiation, a process important in memory formation. Because isoflurane affects memory, we tested whether isoflurane interfered with the translocation of CaM to the neuronal cell nucleus and attenuated the formation P-CREB.

METHODS: SH-SY5Y cells, a human neuroblastoma cell line, were cultured. Cells were depolarized with KCl and the phosphorylation of CREB examined by Western blotting, enzyme-linked immunosorbant assay, and immunocytochemistry. The translocation of CaM from the cytosol to the nucleus was also examined after depolarization. Cells were depolarized and lysed and fractionated by centrifugation to determine the amount of CaM translocated to the nucleus. CaM was localized by immunocytochemistry and quantitated by Western blotting and imaging. Before and during KCl depolarization, cells were exposed to isoflurane, isoflurane plus Bay K 8644, nitrendipine, and -conotoxin GVIa, respectively.

RESULTS: P-CREB increased after KCl depolarization. The increase of P-CREB peaked at depolarization duration of 30 s. The increase in P-CREB formation was inhibited by nitrendipine, but not -conotoxin, and by isoflurane in a concentration-dependent fashion. Pretreatment with the L-type Ca²⁺ channel agonist, Bay K 8644, attenuated the inhibition of P-CREB formation by isoflurane. CaM presence in the nucleus occurred after KCl depolarization. CaM translocation was inhibited by nitrendipine and attenuated by isoflurane. Bay K 8644 pretreatment decreased the isoflurane inhibition of CaM translocation to the nucleus.

CONCLUSIONS: Our data demonstrate that isoflurane inhibits CaM translocation and P-CREB formation. This most likely occurs through isoflurane inhibition of Ca²⁺entry through L-type Ca²⁺ channels.