Principles of Biochemical Toxicology: Book Review

Principles of Biochemical Toxicolog

Selective inhibition of γ-aminobutyric acid type A receptors in human IMR-32 cells by low concentrations of toluene

Effects of the neurotoxic organic solvent toluene on human neuronal nicotinic acetylcholine (nACh) and gaminobutyric acid type A (GABAA) neurotransmitter receptors were investigated in whole-cell voltage-clamped IMR- 32 neuroblastoma cells. Ion currents evoked by near maximum effective concentrations of 1 mM acetylcholine (ACh) and 1 mM g-aminobutyric acid (GABA) are inhibited by toluene in a concentration-dependent way. Concentration/ effect curves of toluene yield IC50 values of 2769/26 and 399/6 mM and slope factors of 1.49/0.2 and 0.89/0.1 for inhibition of the ACh- and GABA-induced ion currents, respectively. The results demonstrate the selective inhibition of human GABAA receptors by toluene at concentrations comparable with brain concentrations associated with occupational exposure

Sense in Pb2+ sensing

It is generally acknowledged that Pb(2+), which is sequestered by live cells from their direct environment, affects a large number of cellular processes at picomolar to micromolar concentrations. However, resolving the specific molecular targets and mechanisms responsible for the neurotoxic effects of this xenobiotic metal is hampered by the lack of suitable tools to investigate the intracellular dynamics of Pb(2+) at low concentrations. Fluorescent Ca(2+) indicators have been used as Pb(2+) sensors and have proven useful to detect cellular Pb(2+) entry and to estimate the overall intracellular free Pb(2+) concentration associated with adverse cellular effects. Despite the high affinity of these Ca(2+) indicators for Pb(2+), their utility for more advanced studies is limited. This is merely due to their moderate metal selectivity and uncertainties about the subcellular (co)localization of the indicators and the targets. Novel Pb(2+) sensors, specifically developed for this purpose, still lack affinity to sense toxicologically relevant intracellular concentrations of Pb(2+). Nonetheless, the development of genetically encoded protein sensors for Ca(2+), Zn(2+), and, recently, also for Pb(2+) opens a new and promising perspective to resolve spatiotemporal changes in intracellular Pb(2+) in relation to cellular signaling and intracell ular divalent metal homeostasis. Such a development is required for enabling more systematic studies of the intracellular dynamics of Pb(2+), which are essential for progress in mechanistic knowledge and will ultimately reveal the critical toxic targets of Pb(2+) at the subcellular and molecular level

Toluene-induced, Ca2+-dependent vesicular catecholamine release in rat PC12 cells

Acute effects of toluene on vesicular catecholamine release from intact PC12 phaeochromocytoma cells have been investigated using carbon fiber microelectrode amperometry. The frequency of vesicles released is low under basal conditions and is enhanced by depolarization. Toluene causes an increase in basal release frequency. The threshold effect is obtained at 30 mM toluene and the maximum enhancement of basal release is seven-fold at 1 mM toluene. Toluene-induced exocytosis depends on the influx of Ca21 through voltage-activated Ca21 channels, which are blocked by Cd21. Toluene neither affects depolarization-evoked exocytosis, nor the characteristics of release events. It is concluded that toluene-induced vesicular catecholamine release is due to an increase in intracellular Ca21 concentration, whereas basic processes underlying exocytosis do not appear to be affected by toluene at concentrations up to 300 mM