Local anesthetics depolarize mitochondrial membrane potential by intracellular alkalization in rat dorsal root ganglion neurons.
BACKGROUND
Although it has been reported that local anesthetics, especially lidocaine, are cytotoxic, the mechanism is unclear. Depolarization of the mitochondrial membrane potential (DeltaPsim), one of the markers of mitochondrial failure, is regulated by the proton electrochemical gradient (Delta H(+)). Therefore, intracellular pH ([pH]in) and mitochondrial pH ([pH]m) are important factors for modifying DeltaPsim. However, the effects of local anesthetics on [pH]in and [pH]m are unclear. To investigate mitochondrial responses to local anesthetics, we simultaneously measured [pH]m and [pH]in, along with DeltaPsim.


METHODS
The ratiometric fluorescent probe JC-1 and HPTS were used for the simultaneous measurements of DeltaPsim with [pH]in in rat dorsal root ganglion neurons. A carboxy-SNARF-1 fluorescent probe was used to measure [pH]m. Lidocaine, mepivacaine, bupivacaine, procaine, QX-314, a charged form of lidocaine, and ammonium chloride (NH(4)Cl) were evaluated.


RESULTS
DeltaPsim was depolarized and [pH]in was increased by lidocaine, mepivacaine, bupivacaine, and procaine in a dose-dependent manner. Significantly, a relationship between DeltaPsim and [pH]in was observed for lidocaine, mepivacaine, bupivacaine, procaine, and NH(4)Cl perfusion. In contrast, QX-314 did not change DeltaPsim or [pH]in. In low-pH saline (pH6) and in the presence of a weak acid, lidocaine failed to increase [pH]in or depolarize DeltaPsim. The [pH]m was also increased by lidocaine, mepivacaine, bupivacaine, procaine, and NH(4)Cl.


CONCLUSIONS
These results demonstrate that uncharged (base) forms of local anesthetics induce DeltaPsim depolarization. One of the causes is intracellular and mitochondrial alkalization.
Onizuka
Shin
S
Department of Anesthesiology and Faculty of Medicine, University of Miyazaki, Kiyotake, Miyazaki 889-1692, Japan.
Tamura
Ryuji
R
Hosokawa
Nobuko
N
Kawasaki
Yuko
Y
Tsuneyoshi
Isao
I
D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D001578:Benzopyrans; D002138:Calibration; D004305:Dose-Response Relationship, Drug; D005260:Female; D005456:Fluorescent Dyes; D005727:Ganglia, Spinal / Q000166:cytology* / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D009284:Naphthols; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012235:Rhodamines
D000779:Anesthetics, Local; D001578:Benzopyrans; D005456:Fluorescent Dyes; D009284:Naphthols; D012235:Rhodamines; C068301:carboxy-seminaphthorhodaminefluoride