Neurochemistry International 41 (2002) 391–397
Toluene inhibits voltage-sensitive calcium channels expressed
in pheochromocytoma cells
, Timothy J. Shafer
, John J. Woodward
Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA 23298, USA
Neurotoxicology Division, US Environmental Protection Agency, Research Triangle Park, NC 27711, USA
Received 3 October 2001; received in revised form 6 February 2002; accepted 22 February 2002
Commercial solventssuch as toluene are commonly used as drugs of abuse by children and adolescents. The cellular and molecular sites
and mechanisms of actions of these compounds are not well studied but their effects on behavior resemble those of central nervous system
depressants such as alcohol, barbiturates and benzodiazepines. In this study, the effects of toluene on voltage-sensitive calcium channels
(VSCCs) were measured in pheochromocytoma cells. The KCl-induced rise in intracellular calcium as measured by calcium imaging was
cells express mainly the L-type of calcium channel. Toluene (0.3–3000
M) by itself did not affect intracellular calcium levels in resting
cells but dose-dependently inhibited the KCl-induced rise in calcium. This inhibition was substantially reversed upon washout of the
toluene-containing solution. KCl-dependent increases in intracellular calcium in cells differentiated with nerve growth factor (NGF)
were largely insensitive to nifedipine. Toluene produced a greater inhibition of the KCl response in NGF treated cells as compared with
undifferentiated cells. A similar ﬁnding was obtained when whole-cell patch-clamp-electrophysiology was used to directly monitor the
effectsof toluene on voltage-activated calcium currents in undifferentiatedand differentiatedcells. These results showthat dihydropyridine
sensitive and insensitive calcium channels are inhibited by toluene and may represent important sites of action for this compound.
Published by Elsevier Science Ltd.
Keywords: Abused solvents; Calcium channels; Calcium imaging
Volatile solvents, such as toluene, make up a large class of
abused inhalants that are found in commercial and industrial
products including paints, paint thinners, adhesives, glue,
gasoline, and cleaning agents (Arlien-Soborg, 1992). Recent
surveys have reported that a signiﬁcant number of adoles-
cents around the world use volatile solvents for recreational
purposes (Neumark et al., 1998). These compounds are ad-
ministered by “hufﬁng” or “snifﬁng” concentrated vapors
arising from solvent-soaked rags or containers (McGarvey
et al., 1999; Streicher et al., 1981). Despite the widespread
abuse of toluene and other solvents, the molecular sites of
This article has been reviewed by the National Health and Environmen-
tal Effects Research Laboratory, US Environmental Protection Agency,
and is approved for publication. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
Corresponding author. Present address: Department of Physiology and
Neuroscience, Medical University of South Carolina, 67 President St,
IOP4N, P.O. Box 250861, Charleston, SC 29425, USA.
Tel.: +1-843-792-5225; fax: +1-843-792-7353.
E-mail address: email@example.com (J.J. Woodward).
action of these compounds are largely unknown (Balster,
More is known about the behavioral effects of these
substances and toluene and other abused solvents produce
effects similar to that of central nervous system depres-
sants. These include psychomotor impairment (Moser and
Balster, 1986), excitation and then inhibition of locomotor
activity (Bushnell et al., 1985; Warren et al., 2000) and loss
of righting reﬂex and sedation (Tegeris and Balster, 1994).
In addition, abused solvents possess anti-convulsant and
anti-anxiety effects (Echeverria et al., 1991; Wood et al.,
1984) and produce ethanol-like discriminative stimulus ef-
fects in mice (Rees et al., 1987). Finally, toluene and other
solvents produce concentration-dependent effects on mea-
sures of cognitive activity in both animals (Bushnell et al.,
1994) and man (Echeverria et al., 1991).
These ﬁndings suggest that toluene and other abused
solvents may share similar sites of action with CNS de-
pressants. These compounds act primarily by altering the
function of both voltage-activated and ligand-gated ion
channels. For example, recent studies using recombinant
expression systems have shown that toluene and related
0197-0186/02/$ – see front matter. Published by Elsevier Science Ltd.