Differential inhibition of neuronal Na+-Ca2+ exchange versus store-operated Ca2+ channels by volatile anesthetics in pheochromocytoma (PC12) cells.
BACKGROUND
Ca2+ influx is a key component of neuronal intracellular Ca2+ ([Ca2+]i) regulation. The authors hypothesized that volatile anesthetic inhibition of neuronal activity is mediated by inhibition of Ca2+ influx via two major mechanisms: plasma membrane Na+-Ca2+ exchange (NCX) and the novel mechanism of Ca2+ influx triggered by endoplasmic reticulum Ca2+ depletion (store-operated Ca2+ channels [SOCCs]).


METHODS
Differentiated rat pheochromocytoma cells loaded with the Ca2+ indicator fura-2 were Na+-loaded with 0 Ca2+, 145 mm Na+ Tyrode's and 5 microm cyclopiazonic acid plus 10 microm ryanodine (functionally isolating plasma membrane). Influx-mode NCX was rapidly reactivated by 0 Na+ and 2.5 mm Ca2+. The protocol was repeated in the presence of volatile anesthetics (0.5-1.5 minimum alveolar concentration [MAC] halothane, isoflurane, or sevoflurane) or other drugs to characterize NCX. To examine SOCCs, endoplasmic reticulum Ca2+ was depleted by cyclopiazonic acid in 0 extracellular Ca2+, and Ca2+ influx was triggered by rapid reintroduction of extracellular Ca2+. The protocol was repeated in the presence of anesthetics or other drugs to characterize SOCCs.


RESULTS
Influx via NCX was not inhibited by voltage-gated Ca2+ channel blockers but was sensitive to NCX inhibitors. Halothane and isoflurane (0.5-1.5 MAC) significantly inhibited NCX (P < 0.05; paired comparisons), whereas sevoflurane at less than 1.5 MAC did not inhibit NCX. SOCC-mediated Ca2+ influx was insensitive to a variety of Ca2+ channel blockers but was inhibited by Ni2+. Such influx was sensitive only to halothane at greater than 1 MAC but not isoflurane or sevoflurane.


CONCLUSIONS
These data indicate that volatile anesthetics, especially halothane and isoflurane, interfere with neuronal [Ca2+]i regulation by inhibiting NCX but not SOCC-mediated Ca2+ influx (except high concentrations of halothane).
Department of Anesthesiology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Binnaz
B
Ay
Daniel
D
Wallace
Carlos B
CB
Mantilla
Yedotore S
YS
Prakash
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D009433:Neural Inhibition / Q000187:drug effects* / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D016716:PC12 Cells; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D014835:Volatilization
D018685:Anesthetics, Inhalation; D015220:Calcium Channels; D019831:Sodium-Calcium Exchanger; D002118:Calcium