Influences of nanoparticle zinc oxide on acutely isolated rat hippocampal CA3 pyramidal neurons

The effects of zinc oxide nanoparticles (nano-ZnO) on the properties of voltage-dependent sodium, potassium currents and evoked action potentials were studied in acutely isolated rat hippocampal CA3 pyramidal neurons at postnatal ages of 10-14 days rats using the whole-cell patch-clamp technique. The results indicated that: (1) in the present of final concentration of 10(-4) g/ml nano-ZnO, the current-voltage curve of sodium current UNA was decreased, and the peak amplitudes Of I-Na were increased considerably from -50 to +20 mV (p < 0.05). Meanwhile, the inactivation and the recovery from inactivation of I-Na were also promoted by the nano-ZnO solution (10(-4) g/ml) (p < 0.01). However, the steady-state activation curve of I-Na was not shifted by the nano-ZnO. (2) The amplitudes of transient outward potassium current (I-A) were increased by the nano-ZnO solution (10(-4) g/ml), while the current-voltage curve of delayed rectifier potassium current (I-K) was significantly increased from +20 to +90 mV (p < 0.05). However, it is apparent that the nano-ZnO solution did not shift the steady-state activation curve of IA and I-K, and neither had significant effects on the inactivation and the recovery from inactivation Of I-A (3) Peak amplitude and overshoot of the evoked single action potential were increased and half-width was diminished in the presence of the 10(-4) g/ml nano-ZnO solution (p < 0.05). Simultaneously, a prolonged depolarizing current injection enhanced (p < 0.05) repetitive firing evoked firing rate. These results suggested that 10(-4) g/ml nano-ZnO solution can lead to an enhancement in the current amplitudes Of I-Na and IK by increasing the opening number of sodium channels, delaying rectifier potassium channels, and enhancing the excitability of neurons, which lead to Na+ influx and the accumulation of intracellular Na+, as well as K+ efflux plus the loss of cytoplasmic K+. These may disturb the ionic homeostasis and the physiological functions of neurons. (C) 2008 Elsevier Inc. All rights reserved.