Volatile Anesthetic Depression of Ca2+ Entry Into and Glutamate Release from Cultured Cerebellar Granule Neurons

Background: Volatile anesthetics (VAs) are known to have actions on a variety of ligand- and voltage gated ion channels, and thereby inhibit neuronal function. VA effects mediated by actions on voltage-gated Ca channels (VGCCs) were determined by studying their effects on the depolarization-induced rise in intracellular Ca2+ transients and the consequent glutamate release in cultured neonatal rat cerebellar granule neurons. Methods: Using a glutamate dehydrogenase-coupled assay for glutamate release, and fura-2 to measure intracellular [Ca2+] ([Ca2+]i), neurons at 37℃ were depolarized by a rapid increase in [K+]o from 5 to 55 mM.  Actions of halothane, isoflurane, enflurane, and sevoflurane were compared with effects of altered [Mg2+]o, and by specific blockade of L-, P/Q- and/or N-type VGCC by nicardipine, ω-agatoxin IVA, and ω-conotoxin-GVIA, respectively.  Whole-cell patch-clamp studies in these same neurons of VGCC Ba2+ currents were also performed at 22℃. Results: Clinical VA concentrations dose-dependently depressed both peak [Ca2+]i and glutamate release by 35-70%.  With N- and/or L-type VGCC blockade, VAs caused a further marked decrease in [Ca2+]i transients. VAs depressed whole cell patch-clamped Ba2+ currents in these granule cell neurons by 35-40%. Conclusions: VAs depress Ca2+ entry by inhibiting a variety of VGCCs, and thereby reduce neuronal glutamate release. This action may contribute to the mechanism of anesthesia as well as provide protection during ischemic insults that cause neuronal injury.  Citation: Carl Lynch III, Ning Miao, Kaoru Nagao, Joseph J. Pancrazio. Volatile anesthetic depression of Ca2+ entry into and glutamate release from cultured cerebellar granule neurons. J Anesth Perioper Med 2017; 4: 45-59. doi:10.24015/JAPM.2017.0016This is an open-access article, published by Evidence Based Communications (EBC). This work is licensed under the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium or format for any lawful purpose. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.