The inhibition of neuronal calcium ion channels by trace levels of yttrium released from carbon nanotubes

Abstract

Carbon nanotubes (CNTs) are used with increasing frequency in neuroengineering applications. CNT scaffolds are used to transmit electrical stimulation to cultured neurons and to control outgrowth and branching patterns of neurites. CNTs have been reported to disrupt normal neuronal function including alterations in endocytotic capability and inhibition of ion channels. Calcium ion channels regulate numerous neuronal and cellular functions including endo and exocytosis, neurite outgrowth, and gene expression. Strong CNT interactions with neuronal calcium ion channels would have profound biological implications. Here we show that physiological solutions containing CNTs inhibit neuronal voltage-gated calcium-ion channels in a dose dependent and CNT-sample-dependent manner with IC50 as low as 1.2 ug/ml. Importantly, we demonstrate that the inhibitory activity does not involve tubular graphene as previously reported, but rather very low concentrations of soluble yttrium released from the nanotube growth catalyst. Cationic yttrium potently inhibits calcium ion channel function with an inhibitory efficacy, IC50, of 0.07 ppm w/w. Because of this potency, unpurified and even some reportedly “purified” CNT samples contain sufficient bioavailable yttrium to inhibit channel function. Our results have important implications for emerging nano-neurotechnology and highlight the critical role that trace components can play in the biological response to complex nanomaterials.

Methodological considerations for testing the ecotoxicity of carbon nanotubes and fullerenes: Review

“…Characterizing starting materials is essential, because CNPs can contain substances (including chemicals known to be toxic) in addition to the CNPs themselves [34][35][36] and because the purity of the CNP material is frequently unreliable, based only on the manufacturer's information. Large differences in reported toxicity of CNPs in the literature are likely a consequence of investigators actually testing different materials, starting materials containing varying amounts of contamination, and variable aggregation of the NPs occurring in the test solution.…”

“…For example, it was observed recently that yttrium released from CNTs affected the functioning of neuronal Ca channels [34], a large concentration of bioavailable Ni was found in unpurified CNTs [35], and the impact of released metals was suggested as a potential cause of the differing effects of exposure to SWNT and double-walled carbon nanotubes (DWNT) on zebrafish embryos [112]. Metals leached from as-prepared fullerenes and metallofullerenes were previously shown to be highly toxic [36].…”

Implantable Electrodes with Carbon Nanotube Coatings

“…It was speculated that the inhibitory effect on PC12 cells was due to CNTs physically interacting with amino-acid residues of the channel pore. The reduction of calcium and potassium currents by CNTs further demonstrates the impact of carbon nanotube on neuronal physiology (Jakubek et al, 2009;Xu et al, 2009). However, in all of these studies the cell lines were exposed to CNTs that were dispersed in the cell media and available for immediate cellular uptake.…”

Nanotubos de carbono aplicados às neurociências: perspectivas e desafios

“…Entretanto, experimentos utilizando tais nanopartículas como suporte para proliferação neuronal revelaram crescimentos celulares alterados 62,63 . Além disso, estudos sugerem que os NTCs alteram as funções neuronais cálcio-dependentes, mediante a obstrução física dos canais iônicos 64 .…”

“…Eles ainda investigaram a natureza das interações neurônio-NTC e propuseram que NTCs estimulam a transmissão do sinal neuronal por meio da formação de vias adicionais de acoplamento elétrico entre os componentes neuronais somáticos e dendríticos. Análises das propriedades eletrofisiológicas das membranas de neurônios hipocampais cultivados em NTCs não revelaram qualquer alteração de condutividade iônica 17,65 , embora estudos mais recentes tenham demonstrado alterações das funções celulares cálcio-dependentes, sugerindo que NTCs podem ocluir fisicamente os canais iônicos 64 .…”