Sevoflurane depolarizes pre-synaptic mitochondria in the central nervous system.
BACKGROUND
Volatile anaesthetics protect the heart from ischaemic injury by activating mitochondrial signalling pathways. The aim of this study was to test whether sevoflurane, which is increasingly used in neuroanaesthesia, affects mitochondrial function in the central nervous system by altering the mitochondrial membrane potential (DeltaPsi(m)).


METHODS
In order to correlate free cytosolic Ca(2+) ([Ca(2+)](i)) and DeltaPsi(m), rat neural presynaptic terminals (synaptosomes) were loaded with the fluorescent probes fura-2 and JC-1. During sevoflurane exposure, 4-aminopyridine (4-AP) 500 micro M to induce pre-synaptic membrane depolarization or carbonylcyanide-p-(trifluoromethoxy)-phenylhydrazone (FCCP) 1 micro M to induce maximum mitochondrial depolarization was added. In order to block mitochondrial ATP-regulated K(+)-channels (mitoK(ATP)), the antagonist 5-hydroxydecanoate (5-HD) 500 micro M was added.


RESULTS
In Ca(2+)-containing medium, both sevoflurane 1 and 2 MAC gradually decreased the normalized JC-1 ratio from 0.96 +/- 0.01 in control to 0.92 +/- 0.01 and 0.89 +/- 0.01, representing a depolarization of DeltaPsi(m) (n = 9, P < 0.05). Sevoflurane 2 MAC increased [Ca(2+)](i). In Ca(2+)-depleted medium, sevoflurane 1 and 2 MAC depolarized DeltaPsi(m), while [Ca(2+)](i) remained unaltered. Sevoflurane 2 MAC attenuated the 4-AP-induced depolarization of DeltaPsi(m). When mitoK(ATP) was blocked, the sevoflurane-induced depolarization of DeltaPsi(m) was attenuated, but not blocked. The depolarizing effect of sevoflurane on DeltaPsi(m) compared with FCCP was calculated to 13.2 +/- 1.3% in Ca(2+)-containing and 15.1 +/- 1.2% in Ca(2+)-depleted medium (n = 7).


CONCLUSIONS
Sevoflurane depolarizes DeltaPsi(m) in rat synaptosomes, and the effect is not dependent on Ca(2+)-influx to the cytosol. Opening of mitoK(ATP) is partly responsible for the depolarizing effect of sevoflurane.
Moe
M C
MC
Institute for Surgical Research and Department of Neurosurgery, Rikshospitalet University Hospital, 0027 Oslo, Norway. cmoe@klinmed.uio.no
Bains
R
R
Vinje
M L
ML
Larsen
G A
GA
Kampenhaug
E B
EB
Berg-Johnsen
J
J
D015761:4-Aminopyridine / Q000008:administration & dosage; D000255:Adenosine Triphosphate; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000008:administration & dosage / Q000031:analogs & derivatives*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects* / Q000502:physiology; D003652:Decanoic Acids / Q000008:administration & dosage; D005260:Female; D005454:Fluorescence Polarization; D006880:Hydroxy Acids / Q000008:administration & dosage; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000187:drug effects; D008738:Methyl Ethers / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects* / Q000502:physiology; D026902:Potassium Channel Blockers / Q000008:administration & dosage; D015221:Potassium Channels; D017729:Presynaptic Terminals / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D000077149:Sevoflurane; D013574:Synaptosomes / Q000187:drug effects; D013997:Time Factors
D018685:Anesthetics, Inhalation; D000889:Anti-Arrhythmia Agents; D003652:Decanoic Acids; D006880:Hydroxy Acids; D008565:Membrane Proteins; D008738:Methyl Ethers; D026902:Potassium Channel Blockers; D015221:Potassium Channels; C108897:carbonylcyanide 4-trifluoromethoxyphenylhydrazone; C117780:mitochondrial K(ATP) channel; D000077149:Sevoflurane; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C052853:5-hydroxydecanoic acid; D000255:Adenosine Triphosphate; D015761:4-Aminopyridine