Background: Volatile anesthetics may act in part by inhibiting voltage
-dependent calcium channels. The effects of several volatile agents on
three types of calcium channels in a thyroid C-cell line were examine
d. Methods: Whole-cell calcium currents were recorded using standard p
atch clamp techniques. Current-voltage relationships were derived befo
re, during, and after application of isoflurane, enflurane, or halotha
ne. Low-voltage-activated (LVA; T type) calcium currents were isolated
based on the voltage range of activation. High-voltage-activated (HVA
) calcium currents were separated into L and N types using omega-conot
oxin GVIA (omega-CTX) and nicardipine. Results: All three agents rever
sibly decreased both LVA and HVA currents at clinically relevant conce
ntrations. Isoflurane and enflurane both reduced peak LVA current more
than peak HVA current: -33 +/- 6% (mean +/- SE) versus -22 +/- 4% for
0.71 mM isoflurane (n = 6), and -46 +/- 6% versus -35 +/- 5% for 1.21
mM enflurane (n = 6). In contrast, halothane depressed LVA and HVA cu
rrents to a similar extent: -22 +/- 4% versus -29 +/- 3% for 0.65 mM h
alothane (n = 6). Isoflurane had no effect on LVA whole-cell current k
inetics. Pretreatment with either omega-CTX (400 nM) or nicardipine (1
mu M) did not change the sensitivity of HVA current to isoflurane. Co
nclusions: Isoflurane and enflurane block LVA calcium channels more po
tently than either L-type or N-type calcium channels, but halothane sh
ows no such preferential effect. These results may have implications f
or the mechanism action of volatile anesthetics.