Effect Of Lanthanum On Potassium Channel In Cell Membrane

There were some special functions and effects of rare earth elements (REEs) on organisms, such as promoting growth and development of plant, increasing the biomass of plant, improving the quality of products and enhancing the ability of plant to resist the adverse environment. Thus, REEs have been widely used in agriculture in China and some other countries, which accelerates the transport and accumulation of REEs in the ecological environment of plant. Meanwhile, REEs have been also widely used in many other fields, such as industry, medicine and environmental protection, leading to the increase in the risk of the environmental pollution of REEs. REEs entering the environment inevitably influence the growth of plant and even the whole farmland ecosystems. Meanwhile, REEs entering the environment also influence the human health through the food chain. People in the world have doubted and feared the application of REEs. Therefore, it is important to reveal the chemical process of REEs action on living organisms and its effect mechanism, especially the cellular mechanism. The ionic channels in the plasma membrane are the most sensitive system of foreign substances action on living organisms. It is very important to investigate the effect of REEs on the ionic channels in the plasma membrane for understanding the chemical process of REEs action on cell in living organisms and the effect mechanism, as well as for evaluating the environmental safety of REEs in living organisms. Potassium ion (K+) channel is the most widely distributed in living organisms, and it is often used as a typical representative of ionic channels in the plasma membrane of cell. In the present thesis, the effect of rare earth lanthanum ion (La3+) on the K+ channel in the cell membrane and the effect mechanism were investigated by using patch clamp, the new method for detecting the electrochemically inactive ions in the plant cell and quantum chemical calculation in order to further reveal the chemical process of REEs action on cell in living organisms and its effect mechanism. The main results from our experiments were shown as follows:(1) It was found by patch clamp technique that La3+ inhibits obviously the current of K+ channel in the animal and plant cells, and accelerates the "opening" and "closing" of hERG K+ channel. The effect of the low concentrations of La3+ on the K+ channel is similar to that of the nutrient element, while the effect of the high concentrations of La3+ on the K+ channel is similar to that of heavy rare earth ion (Tb3+) and heavy metal ions (Cd2+ and Pb2+). And the inhibition in the current of the K+ channel follows the order:La3+ <Pb2+<Cd2+<Tb3+. (2) We investigated a new method for detecting the electrochemically inactive ions in the plant cell, constructed a new system for the detection of the "living" cells of plant and then achieved the detection of the exchange ability of K+ in the membrane of the plant "living" cell for the first time. The method compensates for the disadvantage of patch clamp. In the thesis, the content of K+ on the surface of the plant cell in the present of metal ion was detected using the new method. It was found that the low concentration of La3+ promotes the extracellular K+ into the plant cell, leading to the increase in the content of intracellular K+ and then the improvement of the growth and development of cell. The high concentration of La3+ destroys the structure of K+ channel protein, and then inhibits the growth and development of cell. La3+ shows the similar effect with Ca2+. The damage effect of La3+ on the K+ channel in the cell membrane is significantly weaker than that of Tb3+, Cd2+ and Pb2+.(3) The results from quantum chemical calculation indicated that La3+ can interact with the hERG K+ channel protein, and the interaction is multi-sites. The interaction affects or destroys the structure of the K+ channel protein. It is the structural base for the decrease in the function of the K+ channel. Tb3+, Cd2+ and Pb2+ can also interact with the K+ channel protein, formatting the complex between metal and protein. And the binding ability follows the order:Tb3+> Cd2+> Pb2+> La3+.The results mentioned above demonstrated that La3+ can change the structure of the K+ channel protein in the cell membrane, and then affect the function of the K+ channel. It is one of the cellular mechanisms of REEs action on living organisms.