Voltage-dependent effect of Al3+ on channel activities in hippocampal neurons

A novel isophorone-based fluorescent probe for recognition of Al3+ and its bioimaging in cells and plants

In this work, a novel isophorone-based fluorescent probe H-1 was designed and synthesized. The probe H-1 could achieve highly selective detection of Al³⁺ through forming a 1:1 complex, with a recognition mechanism based on intramolecular charge transfer (ICT). The detection limit of the probe H-1 for Al³⁺ is as low as 8.25 × 10^-8 M which was determined by fluorescent titration. It is confirmed that H-1 could be used not only for fluorescence spectrometry to detect Al³⁺ ions in actual water samples, but also for biological imaging to detect Al³⁺ ions in cells and plants.

Early-life exposure to aluminum and fine motor performance in infants: a longitudinal study

BACKGROUND

Aluminum (Al) is a well-established neurotoxicant. However, little is known about its effects on the neurodevelopment of infants.

OBJECTIVES

To examine early-life exposure to Al in relation to neurodevelopment in healthy infants.

METHODS

Nail Al concentrations were measured among 747 newborn babies within 6 months of delivery in the Shanghai Birth Cohort. Neurodevelopment was assessed using Ages and stages questionnaire (third edition, ASQ-3) at ages 6 and 12 months. General linear regression models were performed to estimate the associations between Al concentrations and ASQ-3 scores.

RESULTS

After adjustment for potential confounders, early-life exposure to Al was not associated with any neurodevelopmental performance at age 6 months. However, Al level was associated with an increased risk of having a low fine motor score (quartile 4 vs. quartile 1, mean difference (MD): -1.63; 95% confidence interval (CI): -3.22, -0.05; P-trend < 0.01) at 12 months. No association was found for communication, gross motor, problem-solving, or personal-social score at 12 months.

SIGNIFICANCE

Early-life exposure to Al may be associated with poor fine motor skills in a dose-response manner among apparently healthy infants at age 12 months.

Link between Aluminum and the Pathogenesis of Alzheimer's Disease: The Integration of the Aluminum and Amyloid Cascade Hypotheses

Whilst being environmentally abundant, aluminum is not essential for life. On the contrary, aluminum is a widely recognized neurotoxin that inhibits more than 200 biologically important functions and causes various adverse effects in plants, animals, and humans. The relationship between aluminum exposure and neurodegenerative diseases, including dialysis encephalopathy, amyotrophic lateral sclerosis and Parkinsonism dementia in the Kii Peninsula and Guam, and Alzheimer's disease (AD) has been suggested. In particular, the link between aluminum and Alzheimer's disease has been the subject of scientific debate for several decades. However, the complex characteristics of aluminum bioavailability make it difficult to evaluate its toxicity and therefore, the relationship remains to be established. Mounting evidence has suggested that significance of oligomerization of β-amyloid protein and neurotoxicity in the molecular mechanism of AD pathogenesis. Aluminum may play crucial roles as a cross-linker in β-amyloid oligomerization. Here, we review the detailed characteristics of aluminum neurotoxicity based on our own studies and the recent literatures. Our aim is to revisit the link between aluminum and AD and to integrate aluminum and amyloid cascade hypotheses in the context of β-amyloid oligomerization and the interactions with other metals.

Potentiation of the nicotinic acetylcholine receptor by aluminum in mammalian neurons

Aluminum (Al(3+)), a known neurotoxic substance, has long been implicated in the pathogenesis of Alzheimer's disease and other neurodegenerative diseases. Al(3+) targets many ligand-gated and voltage-gated ion channels and modulates their functions. In the present study, the actions of Al(3+) on the nicotinic acetylcholine receptor (nAChR) were investigated by whole-cell patch clamp technique in acutely isolated rat trigeminal ganglion neurons. We observed that Al(3+) potentiated nicotine-evoked inward currents in a concentration-dependent manner (10-1000 microM). The effects of Al(3+) on nicotine-evoked currents were voltage independent. Al(3+) appeared to increase the affinity of nicotine to nAChR but not the efficacy. Al(3+) reduced the agonist concentration producing a half-maximal response (EC(50)) for nicotine from 74.4+/-1.9 microM to 32.9+/-2.6 microM, but did not alter the threshold nor maximal response. On the contrary, another trivalent cation, Ga(3+), had little effect on nicotine-evoked currents. The present results indicated that Al(3+) enhanced the function of nAChR and this potentiation might underlie the neurological alteration induced by Al(3+).

Does neurotransmission impairment accompany aluminium neurotoxicity?

Neurobehavioral disorders, except their most overt form, tend to lie beyond the reach of clinicians. Presently, the use of molecular data in the decision-making processes is limited. However, as details of the mechanisms of neurotoxic action of aluminium become clearer, a more complete picture of possible molecular targets of aluminium can be anticipated, which promises better prediction of the neurotoxicological potential of aluminium exposure. In practical terms, a critical analysis of current data on the effects of aluminium on neurotransmission can be of great benefit due to the rapidly expanding knowledge of the neurotoxicological potential of aluminium. This review concludes that impairment of neurotransmission is a strong predictor of outcome in neurobehavioral disorders. Key questions and challenges for future research into aluminium neurotoxicity are also identified.

Expression profiles of voltage-gated Na(+) channel alpha-subunit genes in rat and human prostate cancer cell lines

BACKGROUND

Voltage-gated Na(+) channel (VGSC) activity has been implicated in prostate cancer (PC) metastasis. Although VGSCs can occur as multiple-subunit assemblies, the alpha-subunits (VGSCalphas) alone can encode functional channels. The VGSCalpha gene(s) responsible for the functional VGSCalpha expression in strongly metastatic PC cell lines is not known.

METHODS

Two reverse transcription-PCR (RT-PCR) methods, degenerate primer screening and a novel semi quantitative PCR (SQT-PCR) technique, were used. These methods enabled a detailed qualitative and quantitative investigation of VGSCalpha mRNA expression in rat (MAT-LyLu/AT-2) and human (PC-3/LNCaP) PC cells of markedly different metastatic potential.

RESULTS

Expression of eight different VGSCalpha genes (SCN1A-4A, SCN7A-9A, and SCN11A) was determined in the PC cell lines. Most were expressed as multiple splice variants. SQT-PCR results were consistent with a basal level of VGSCalpha mRNA expression occurring in weakly metastatic (AT-2/LNCaP) cells, and this being greatly elevated in cells of stronger metastatic potential (MAT-LyLu/PC-3), primarily due to the elevated expression of the SCN9A gene (also termed PN1/hNe-Na).

CONCLUSIONS

(1) Several VGSCalpha genes and their splice variants are expressed similarly in both rat and human PC cell lines. (2) Expression levels are much higher in the strongly metastatic (MAT-LyLu/PC-3) cells. (3) Levels of SCN9A mRNA specifically are predominant in MAT-LyLu and PC-3 cells; thus, SCN9A is highly likely to be the main source of the functional VGSC detected.

ATP modulates Na+ channel gating and induces a non-selective cation current in a neuronal hippocampal cell line

Extracellular ATP evoked two excitatory responses in hippocampal neuroblastoma cells (HN2). The first, an opening of a receptor-operated non-selective cation channel and the second was a leftward shift in Na+ channel activation. Both ATP (5-1000 microM) and 2',3'-(4-benzoyl)-benzoyl-ATP (Bb-ATP, 50 microM) activated a non-selective cation current reversing near 0 mV and shifted the Na+ activation and inactivation curves to the left. Based on a comparison of a series of agonists and antagonists, the inward current appeared to be partially mediated by activation of a P2X7 receptor, although hybrid channels cannot be ruled out. The shift in Na+ channel gating could be separated from the opening of the cation channel, as application of the P2Y antagonist Reactive Blue-2 and GTP shifted the Na+ current activation to the left but failed to elicit the inward cation current. Both responses to ATP and Bb-ATP were insensitive to block by the P2X antagonist suramin (300 microM) but were prevented by incubation in oxidized ATP (200 microM); a putative P2X7 receptor antagonist. Prior screening of the surface negative charge of the membrane with a high concentration of divalent cations prevented both responses. We suggest that ATP4- activates a P2X receptor and becomes trapped on a site, on or near the Na+ channel. Activation of the P2X receptor leads to the opening of a non-specific cation channel, while the binding of ATP4- leads to a modified charge sensed by the Na+ channel, similar to what occurs in the presence of charged amphiphiles as well as a number of beta-scorpion toxins.

pH-dependent actions of aluminum on voltage-activated sodium currents in snail neurons

The pH-dependent actions of aluminum(III) hydroxides (Al(III))on the voltage-activated sodium currents (VASCs) in the giant neurons of the pond snail Lymnaea stagnalis L. were studied by means of a conventional two-electrode voltage-clamp technique. The final concentration of Al(III) was 5-500 microM at pH 7.7, 6.9 or 6.0. A significant and concentration-dependent increase in the peak amplitude of the VASCs was recorded over the entire voltage range at pH 7.7 (EC50 = 100.7 +/- 33.7 microM, n = 9), without alteration of the gating properties. A concentration-dependent decrease in the peak amplitude (IC50 = 175.9 +/- 73.6 microM, n = 6) and concomitant increases in the time constants of activation and inactivation of the VASCs were recorded in slightly acidic media (pH 6.0), whereas there were no changes in the investigated parameters at pH 6.9. A significant increase in the V1/2 of the half-maximal current of the steady-state inactivation resulted on Al(III) application at pH 7.7, but not at pH 6.9 or 6.0. These results suggest that Al(III) can differentially up- and down-modulate the sodium current and related physiological functions to extents dependent on the pH-determined speciation of the Al(III) hydroxides present.

A molecular mechanism of aluminium-induced Alzheimer's disease?

An abundance of research has continued to link aluminium (Al) with Alzheimer's disease (AD) (Strong et al., J. Toxicol. Environ. Health 48 (1996) 599; Savory et al., J. Toxicol. Environ. Health 48 (1996) 615). Animals loaded with Al develop both symptoms and brain lesions that are similar to those found in AD. However, these animal models of Al intoxication are not representative of human exposure to Al. They have not addressed the significance of a truly chronic exposure to Al. If Al is a cause of AD it is effective at the level of our everyday exposure to the metal and AD will be one possible outcome of the life-long presence of a low, though burgeoning, brain Al burden. Individual susceptibility to AD will be as much to do with differences in brain physiology as with changes in our everyday exposure to the metal. There will be a chemical response and indeed biochemical/physiological response in the brain to Al. The question is whether brain Al homeostasis could impact upon brain function. In reviewing the recent literature covering the neurotoxicity of Al and, in particular, of the known and probable mechanisms involved in brain Al homeostasis I have identified a mechanism through which a truly chronic exposure to Al would bring about subtle and persistent changes in neurotransmission which, in time, could instigate the cascade of events known collectively as AD. This mechanism involves the potentiation of the activities of neurotransmitters by the action of Al-ATP at adenosine 5'-triphosphate (ATP) receptors in the brain.

Selective modulation of GABAA receptors by aluminum

Aluminum has been implicated in several neurodegenerative conditions including Alzheimer's disease. Because the mammalian olfactory system has an unusual capacity for the uptake and transneuronal spread of inhaled substances such as aluminum, whole cell recording techniques were used to examine the actions of aluminum on basic membrane properties and amino acid receptors on rat olfactory bulb mitral/tufted (M/T) neurons in culture. Aluminum had little direct effects on M/T neurons. Aluminum (100 microM) did not evoke a membrane current or alter action-potential shape or duration. Aluminum also had no marked effects on the family of voltage-gated membrane currents evoked by a series of 10-mV, 50-ms depolarizing steps. However, aluminum dramatically potentiated the current evoked by 30 microM gamma-aminobutyric acid (GABA) at concentrations <100 microM. Conversely, higher concentrations of aluminum blocked the GABA-evoked current. The effects of aluminum on GABA-evoked currents were not voltage dependent. Aluminum (100 microM) equally potentiated both inward currents at -30 mV and outward currents at + 30 mV. At 300 microM, aluminum blocked both inward and outward currents to a similar extent. In some neurons, aluminum only blocked the current and potentiation was not observed. The biphasic action of aluminum on GABA-evoked currents suggests separate binding sites: a high-affinity potentiating site and a low-affinity inhibiting site. Despite its effects on GABA-evoked currents, aluminum did not alter membrane currents evoked by glutamate, N-methyl-D-aspartate, kainate, or glycine. Aluminum also did not reduce spontaneous excitatory synaptic activity, suggesting little, if any, effect on glutamate release. Although a causal role for aluminum in Alzheimer's disease and other neuropathological conditions remains controversial, it is clear that elevated aluminum concentrations in the brain are associated with a variety of cognitive impairments. The present results indicate that aluminum can alter the function of GABAA receptors and may suggest that aluminum can contribute to cognitive impairment through disruption of inhibitory circuits.