Bupivacaine Indirectly Potentiates Glutamate-induced Intracellular Calcium Signaling in Rat Hippocampal Neurons by Impairing Mitochondrial Function in Cocultured Astrocytes

• Published in: Anesthesiology (Philadelphia) 2018-03, Vol.128 (3), p.539-554
• Main Authors: Xing, Yuan, Zhang, Nan, Zhang, Wei, Ren, Lei-Ming
• Format: Article
• Language: English
• ISSN: 0003-3022; 1528-1175
• DOI: 10.1097/ALN.0000000000002003

BACKGROUND:Bupivacaine induces central neurotoxicity at lower blood concentrations than cardiovascular toxicity. However, central sensitivity to bupivacaine is poorly understood. The toxicity mechanism might be related to glutamate-induced excitotoxicity in hippocampal cells. METHODS:The intracellular free Ca concentration ([Ca]i), mitochondrial membrane potential, and reactive oxygen species generation were measured by fluorescence and two-photon laser scanning microscopy in fetal rat hippocampal neurons and astrocytes. RESULTS:In astrocyte/neuron cocultures, 300 μM bupivacaine inhibited glutamate-induced increases in [Ca]i in astrocytes by 40% (P < 0.0001; n = 20) but significantly potentiated glutamate-induced increases in [Ca]i in neurons by 102% (P = 0.0007; n = 10). Ropivacaine produced concentration-dependent effects similar to bupivacaine (0.3 to 300 μM). Tetrodotoxin did not mimic bupivacaine’s effects. In pure cell cultures, bupivacaine did not affect glutamate-induced increases in [Ca]i in neurons but did inhibit increased [Ca]i in astrocytes. Moreover, bupivacaine produced a 61% decrease in the mitochondrial membrane potential (n = 20) and a 130% increase in reactive oxygen species generation (n = 15) in astrocytes. Cyclosporin A treatment suppressed bupivacaine’s effects on [Ca]i, mitochondrial membrane potential, and reactive oxygen species generation. When astrocyte/neuron cocultures were incubated with 500 μM dihydrokainic acid (a specific glutamate transporter–1 inhibitor), bupivacaine did not potentiate glutamate-induced increases in [Ca]i in neurons but still inhibited glutamate-induced increases in [Ca]i in astrocytes. CONCLUSIONS:In primary rat hippocampal astrocyte and neuron cocultures, clinically relevant concentrations of bupivacaine selectively impair astrocytic mitochondrial function, thereby suppressing glutamate uptake, which indirectly potentiates glutamate-induced increases in [Ca]i in neurons.