Isoflurane inhibition of endocytosis is an anesthetic mechanism of action

• Published in: Current biology Vol. 32; no. 14; pp. 3016 - 3032.e3
• Main Authors: Jung, Sangwook, Zimin, Pavel I., Woods, Christian B., Kayser, Ernst-Bernhard, Haddad, Dominik, Reczek, Colleen R., Nakamura, Ken, Ramirez, Jan-Marino, Sedensky, Margaret M., Morgan, Philip G.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 25.07.2022
• Subjects: Adenosine Triphosphate; Anesthetics, Inhalation - pharmacology; Animals; ATP; complex I; Electron Transport Complex I - genetics; Endocytosis; exocytosis; Glucose; Isoflurane - pharmacology; Mice; mitochondria; mouse; presynapse; volatile anesthetics; mouse; presynapse; mitochondria; complex I; endocytosis; volatile anesthetics; exocytosis; ATP
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2022.05.037

The mechanisms of volatile anesthetic action remain among the most perplexing mysteries of medicine. Across phylogeny, volatile anesthetics selectively inhibit mitochondrial complex I, and they also depress presynaptic excitatory signaling. To explore how these effects are linked, we studied isoflurane effects on presynaptic vesicle cycling and ATP levels in hippocampal cultured neurons from wild-type and complex I mutant (Ndufs4(KO)) mice. To bypass complex I, we measured isoflurane effects on anesthetic sensitivity in mice expressing NADH dehydrogenase (NDi1). Endocytosis in physiologic concentrations of glucose was delayed by effective behavioral concentrations of isoflurane in both wild-type (τ [unexposed] 44.8 ± 24.2 s; τ [exposed] 116.1 ± 28.1 s; p < 0.01) and Ndufs4(KO) cultures (τ [unexposed] 67.6 ± 16.0 s; τ [exposed] 128.4 ± 42.9 s; p = 0.028). Increasing glucose, to enhance glycolysis and increase ATP production, led to maintenance of both ATP levels and endocytosis (τ [unexposed] 28.0 ± 14.4; τ [exposed] 38.2 ± 5.7; reducing glucose worsened ATP levels and depressed endocytosis (τ [unexposed] 85.4 ± 69.3; τ [exposed] > 1,000; p < 0.001). The block in recycling occurred at the level of reuptake of synaptic vesicles into the presynaptic cell. Expression of NDi1 in wild-type mice caused behavioral resistance to isoflurane for tail clamp response (EC50 Ndi1(−) 1.27% ± 0.14%; Ndi1(+) 1.55% ± 0.13%) and halothane (EC50 Ndi1(−) 1.20% ± 0.11%; Ndi1(+) 1.46% ± 0.10%); expression of NDi1 in neurons improved hippocampal function, alleviated inhibition of presynaptic recycling, and increased ATP levels during isoflurane exposure. The clear alignment of cell culture data to in vivo phenotypes of both isoflurane-sensitive and -resistant mice indicates that inhibition of mitochondrial complex I is a primary mechanism of action of volatile anesthetics. •Isoflurane inhibits mitochondrial complex I and decreases presynaptic ATP levels•The fall in ATP levels accompanies a failure in endocytosis at the presynapse•NDi1 bypasses complex I and rescues isoflurane’s effects on ATP and endocytosis•NDi1 causes resistance to the behavioral effects of volatile anesthetics. Jung et al. demonstrate that in neuronal cultures, isoflurane decreases presynaptic ATP levels and inhibits presynaptic endocytosis after intense neuronal stimulation. Both effects result from inhibition of mitochondrial complex I. ATP-dependent failure of presynaptic endocytosis is one primary mechanism of action of isoflurane.