ABSTRACT
Carbon nanotubes are electrically conductive and on the same scale as growing neurons. Consequently, nanotubes have been considered in a number of studies as potential novel biomaterials for neuronal growth (Ni et al. 2005) and stimulation (Cellot et al. 2008). Neurons grown in the presence of water soluble, arc-synthesized SWNT functionalized with PEG, demonstrated altered neurite outgrowth patterns consistent with alterations in calcium homeostasis. Using calcium sensitive dyes, Ni et al. showed that upon exposure to SWNT-PEG, the intracellular calcium levels were not being restored, suggesting SWNT-PEG was an inhibitor of depolarization-dependent calcium infl ux (Ni et al. 2005). A later study focused on the interaction of arc-synthesized SWNTs on the cultures of primary neurons and glia cells (Belyanskaya et al. 2009). Whole-cell patch clamp recordings of dorsal root ganglia cells exposed to bundled SWNTs revealed diminished inward conductivity and a more positive resting potential. The authors postulate that their results could be explained if VGCCs were affected by the nanotubes (Belyanskaya et al. 2009). Each of these studies utilizes arc-synthesized SWNTs manufactured with nickel/ yttrium catalytic particles and suggests that the SWNTs are affecting the conductance of VGCCs. A more recent study showed that physiological solutions containing arc-synthesized SWNTs (with a Ni/Y catalyst) and surprisingly SWNT-free supernatant, inhibit neuronal VGCCs in a dosedependent and SWNT-sample-dependent manner (Fig. 2). The inhibitory activity involved very low concentrations of soluble yttrium released from the catalytic particle. Yttrium potently inhibits calcium ion channel function with an inhibitory effi cacy, IC50, of 0.07 ppm w/w (Jakubek et al. 2009). As a result of this potency, unpurifi ed and even some “purifi ed” SWNT samples contain suffi cient bioavailable yttrium to potentially inhibit channel function.
