Effects of extracellular potassium diffusion on electrically coupled neuron networks

Detection of K+ Efflux from Stimulated Cortical Neurons by an Aptamer-Modified Silicon Nanowire Field-Effect Transistor

The concentration gradient of K⁺ across the cell membrane of a neuron determines its resting potential and cell excitability. During neurotransmission, the efflux of K⁺ from the cell via various channels will not only decrease the intracellular K⁺ content but also elevate the extracellular K⁺ concentration. However, it is not clear to what extent this change could be. In this study, we developed a multiple-parallel-connected silicon nanowire field-effect transistor (SiNW-FET) modified with K⁺-specific DNA-aptamers (aptamer/SiNW-FET) for the real-time detection of the K⁺ efflux from cultured cortical neurons. The aptamer/SiNW-FET showed an association constant of (2.18 ± 0.44) × 10⁶ M^-1 against K⁺ and an either less or negligible response to other alkali metal ions. The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulation induced an outward current and hyperpolarized the membrane potential in a whole-cell patched neuron under a Na⁺/K⁺-free buffer. When neurons were placed atop the aptamer/SiNW-FET in a Na⁺/K⁺-free buffer, AMPA (13 μM) stimulation elevated the extracellular K⁺ concentration to ∼800 nM, which is greatly reduced by 6,7-dinitroquinoxaline-2,3-dione, an AMPA receptor antagonist. The EC₅₀ of AMPA in elevating the extracellular K⁺ concentration was 10.3 μM. By stimulating the neurons with AMPA under a normal physiological buffer, the K⁺ concentration in the isolated cytosolic fraction was decreased by 75%. These experiments demonstrate that the aptamer/SiNW-FET is sensitive for detecting cations and the K⁺ concentrations inside and outside the neurons could be greatly changed to modulate the neuron excitability.