Effects of Isoflurane on Voltage-Dependent Calcium Fluxes
in Rabbit T-Tubule Membranes: Comparison with Alcohols
Murat Oz,*
,1
Yulia Tchugunova,† Meral Dinc,† and Susan M. J. Dunn‡
*Cellular Neurobiology Section, National Institute on Drug Abuse, 5500 Nathan Shock Drive, Baltimore, Maryland 21224;
†Department of Pulmonary Diseases, Oncological Hospital, Ankara 06947, Turkey; and ‡Department of Pharmacology,
University of Alberta, Edmonton, Alberta T6G 2H7, Canada
Received October 1, 2001; published online January 21, 2002
The effects of racemic () and ()- and ()-stereoiso-
mers of isoflurane on depolarization-induced
45
Ca
2
fluxes mediated by voltage-dependent Ca
2
channels
were investigated in transverse tubule membrane ves-
icles from rabbit skeletal muscle. In the concentration
range 0.5 to 2 mM, ()-isoflurane inhibited
45
Ca
2
fluxes and functionally modulated the effects of the
Ca
2
channel antagonist nifedipine (1–10 M). Isoflu-
rane-induced inhibition of
45
Ca
2
fluxes was not signif-
icantly affected by pretreatment with either pertussis
toxin (5 g/ml) or phorbol 12-myristate 13-acetate (50
nM). Further experiments indicated that there were
no significant differences between ()- and ()-stereo-
isomers of isoflurane with respect to the extent of in-
hibition of
45
Ca
2
fluxes. Radioligand binding studies
indicated that racemic and ()- and ()-isoflurane
were equally effective in displacing the specific bind-
ing of [
3
H]PN 200-110 to transverse tubule membranes.
There were no apparent differences between the ef-
fects of ()- and ()-isoflurane on the characteristics
of [
3
H]PN 200-110 binding. Although the concentra-
tions of isoflurane for the inhibitions of
45
Ca
2
fluxes
and radioligand bindings were similar, the concentra-
tions of n-alcohols required for the inhibition of
45
Ca
2
fluxes were lower than those for the displacement of
radioligand. Comparison of the data for the displace-
ment of [
3
H]PN 200-110 binding and the inhibition of
45
Ca
2
fluxes by isoflurane and by n-alcohols suggested
that both isoflurane and n-alcohols may have more
than a single binding site. In conclusion, results indi-
cate that isoflurane, independent of intracellular Ca
2
levels, nonstereospecifically inhibits the function of
voltage-dependent Ca
2
channels and this effect is me-
diated through multiple binding sites. © 2002 Elsevier
Science (USA)
Key Words: calcium channels; volatile anesthetics;
stereoisomers; alcohols; skeletal muscle.
In the search of potential targets for the cellular and
molecular actions of volatile anesthetics, a number of
ion channels have been investigated (for a review, see
1). In previous studies it has been reported that volt-
age-dependent Ca
2+
channels (VDCCs)
2
of neurons,
smooth and cardiac muscles are affected by these com-
pounds (2– 4). The VDCC of skeletal muscle is the best
characterized Ca
2+
channel subtype in terms of its
molecular structure (5) but there has been no report on
the effect of volatile anesthetics on its function. Fur-
thermore, observations that volatile anesthetics can
have multiple effects at various levels of cellular func-
tion complicate the interpretation of some of the earlier
findings in which intact cells were used. For example,
volatile anesthetics have been shown to release Ca
2+
from intracellular stores of several cell types including
cultured neurons and cardiac and skeletal muscle fi-
bers (6 – 8). Since VDCCs are inactivated by rises in
intracellular Ca
2+
(9 –11), it is possible that some of the
effects of volatile anesthetics are mediated by increases
in intracellular Ca
2+
concentrations. Furthermore, vol-
atile anesthetics have been shown to directly and/or
indirectly (via increases in intracellular Ca
2+
concen-
trations) activate several second messenger systems
including protein kinases C and A and calmodulin (12,
13) which are known to affect the functional properties
of VDCCs. Thus the possible secondary effects of vola-
1
To whom correspondence should be addressed. Fax: (410) 550-
1621. E-mail: moz@intra.nida.nih.gov.
2
Abbreviations used: VDCC, voltage-dependent Ca
2+
channel; T,
transverse; EGTA, ethylene glycol bis (-aminoethyl ether) N, N'-
tetraacetic acid; DMSO, dimethyl sulfoxide; PMA, phorbol 12-myris-
tate 13-acetate; ANOVA, analysis of variance; PTX, pertussis toxin;
DHP, 1,4-dihydropyridine; PN 200-110, isradipine.
0003-9861/02 $35.00 275
© 2002 Elsevier Science (USA)
All rights reserved.
Archives of Biochemistry and Biophysics
Vol. 398, No. 2, February 15, pp. 275–283, 2002
doi:10.1006/abbi.2001.2726, available online at http://www.idealibrary.com on