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  4. Detecting the Monovalent Cation Concentrations at the Vicinity of the Plasma Membrane
 
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Detecting the Monovalent Cation Concentrations at the Vicinity of the Plasma Membrane

Date Issued
2014
Date
2014
Author(s)
Hsu, Wan-Hsuan
URI
http://ntur.lib.ntu.edu.tw//handle/246246/261689
Abstract
An organism utilizes different ions to support various physiological activities. Ca2+ participates in neurotransmitters release and muscle contraction. Na+ is the ion with highest concentration in the body fluid; the increase in the serum Na+ concentration elevates the blood pressure. In conjugation with K+, Na+ is involved in the transmission of nerve impulses. K+ is the most abundant ion inside the cell and regulates many cell activities like membrane permeability, growth, etc. Most importantly, K+ determines the resting membrane potential to modulate the neuron excitability. Because cells are in close contact with each other in tissues, the ion concentration changes at the interstitial microenvironment between cells will affect each other. Therefore, we are interested in understanding the concentrations of Na+ and K+ at both sides of the plasma membrane to verify their contributions to the microenvironment. We first used the Na+ specific fluorescence indicators to investigate the changes of intracellular Na+ concentration ([Na+]i) in primary-cultured neurons. The basal [Na+]i was 16.5 ± 1.6 mM and elevated to 154.0 ± 68.2 mM when stimulated by glutamate (10 μM); the concentration decline gradually afterwards. We used the K+ specific fluorescence indicators to investigate the changes of intracellular K+ concentration ([K+]i) in primary-cultured neurons. The basal [K+]i was 142.5 ± 43.5 mM and decreased to 10.6 ± 0.8 mM when stimulated by glutamate (10 μM); however, the [K+]i did not recover after the stimulation in 2 min. To investigate the K+ efflux at the membrane surface, we modified a K+-specific aptamer on the silicon nanowire field-effect transistor. The binding of K+ onto the apatamer changes the field effect surrounding the nanowire resulting in the conductivity changes. The data shows that the functionalized device responded to different alkali ions with various affinities: K+ (Kd = 7.9 ± 0.4 mM) > Cs+ (Kd = 12.1 ± 0.5 mM) > Na+ (Kd = 24.8 ± 4.1 mM) >> Li+ (Kd = 189.0 ± 44.5 mM). We are currently testing the K+ concentration at the membrane surface by anchoring cell onto the silicon nanowire. These measurements of the ion concentrations at the micro-environment will provide detail information in understanding the neuron-neuron interactions.
Subjects
鈉離子濃度
鉀離子濃度
細胞膜電位
神經傳導
矽奈米線場效電晶體
Type
thesis
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