I am trying to record Glutamate receptor from HEK cells transfected by CaPO4 method (outside out). My internal solution is 115 NaCl, 10 NaF,0.5 CaCl2, 1 MgCl2, 5 Na4BAPTA, 5 HEPES and 10 Na2ATP, pH 7.3. and external solution is (in mM)150 NaCl, 0.1MgCl2, 0.1 CaCl2, 5 HEPES, titrated to pH 7.3 with NaOH, My patch ppt is 2-5Mohm. I see very tiny current ( 25pA) and my hit rate of getting current is also very low. I loose them within 5-7 min. In few paper I saw internal solution instead of sodium they use cesium. Can somebody explain me why cesium is used. glutamate unedite receptor allows sodium ion to pass through it. Will using cesium improve my current?