The cytological and electrophysiological effects of silver nanoparticles on neuron-like PC12 cells

Background: Silver nanoparticles (SNPs) are widely used in a large number of products. SNPs can cross the blood-brain barrier and are subsequently deposited continuously in the brain, causing a variety of pathological responses and diseases. As a result, the toxic effects of SNPs on the nervous system have attracted considerable attention, but the mechanism of toxicity remains unclear. Moreover, neurons have different cytological and electrophysiological properties, and their functions are highly dependent on changes in electrophysiological properties. Results Different concentrations of SNPs (20 nm) were prepared, and the effects of different application durations on the cell viability and electrical excitability of rat adrenal pheochromocytoma (PC12) quasi-neuronal networks were investigated. The effects of 200 µM SNPs on the neurite length, cell membrane potential (CMP) difference, intracellular Ca 2+ content, mitochondrial membrane potential (MMP) difference, adenosine triphosphate (ATP) content, and reactive oxygen species (ROS) content of networks were investigated. The results showed that 200 µM SNPs produced grade 1 cytotoxicity at 48 h of interaction, and the other concentrations of SNPs were noncytotoxic. Noncytotoxic 5 µM SNPs significantly increased the electrical excitability of PC12 quasi-neuronal networks, and noncytotoxic 100 µM SNPs led to an initial increase followed by a significant decrease in electrical excitability. While cytotoxic 200 µM SNPs significantly decreased the electrical excitability. 200 µM SNPs led to decreases in neurite length, MMP difference and ATP content and increases in CMP difference, and intracellular Ca 2+ and ROS levels with increasing interaction time. Conclusions The results above revealed that using only cell viability to evaluate nanoparticles-induced neurotoxicity is partial. Therefore, not only cell viability but also electrophysiological properties should be considered when evaluating nanoparticles-induced neurotoxicity. The SNPs-induced cytotoxicity mainly originated from its effects on ATP content, cytoskeletal structure and ROS content. The SNPs-induced decrease in electrical excitability could be explained by a decrease in ATP content which could lead to cellular energy deficiency that opened K ATP channels on the cell membrane, resulting in an increase in the CMP difference and hyperpolarization. ATP content may thus be an important indicator of both cell viability and electrical excitability of PC12 quasi-neuronal networks.