Collection Of Permeation Ions At The Mouth Of The Pore Remove The Voltage Dependent Block Of Kir2Channel By Extracellular Mg²⁺

The inward rectifier potassium (Kir) channel is a class of transmembrane proteinswhich plays important roles in various physiological processes, such as controlling theresting membrane potential, regulating excitability of cardiac cells and neurons, couplinginsulin secretion and maintaining electrolyte balance. It was named as inward rectification,because of its inward rectified characteristics in voltage current relationship, named that theprocess of potassium ions through Kir channels from extracellular is easier than flowing out.The rectification is not an inherent property of the channel protein itself, but reflects strongvoltage dependence of channel block by intracellular cations such as Mg2+and polyamines.In this study, the authors performed an interactive method between theoretical andexperimental study. We started with electrophysiological recording on Kir2.2and its mutantswhich are exogenously expressed in xenopus laevis oocytes. We found that extracellularMg2+can reduce the currents of WT Kir2.2in a voltage dependent way. The kinetics ofinhibition and recovery of Mg2+is fast, with time constant about3~4s, meanwhile moleculardynamics simulation results also show that there is a Mg2+binding site which is located atthe extracellular mouth of Kir2.2and can voltage-dependently bind Mg2+. The mutations,G119D, Q126E and H128D, increase the collection of permeation K+ions and reduce thevoltage-dependent blockage of Kir2.2.Calcium-activated Chloride Channel (CaCCs) is found in Xenopus oocytes originally.Calcium and voltage dual-dependent activation mechanism of the CaCCs is seemed astypical electrophysiological properties. The CaCCs are widely distributed in various tissuesof vertebrates and invertebrates, and mediate a variety of physiological processes. Therefore,screening the specific inhibitor and agonist for CaCCs is important, especially for the drugtarget.We use high-throughput drug screening by YFP-fluorescence quenching to evaluatewhether the drugs can regulate the function of CaCCs. Our data show that among sixcandidates, UMC, F4and C15had significant inhibitions on CaCCs. C25had a slightlyinhibitory effect on the CaCCs currents. However, DMC and CX have very weak or noeffect on CaCCs.