AIM:To study the effects of extracellular potassium on the protein expression of wild-type HERG and its mutant L539fs/47.METHODS:Wild-type HERG (WT) or its mutant HERG-L539fs/47 (MT) were transfected into HEK293 cells for 36 h.The cells were incubated in different media containing 0.8, 4.3 or 10 mmol/L potassium.Af-ter 6 h of incubation, the protein expression of HERG was detected by flow cytometry.After 12 h of incubation, the locali-zation and quantity of the proteins were detected by laser confocal imaging and Western blot.RESULTS: Different from the retention of mutant protein in cytoplasm, wild-type HERG protein was mainly distributed in the cell membrane.The 2 proteins both increased with the changes of extracellular potassium.Flow cytometry showed that the fluorescence in the 2 groups both increased with the changes of extracellular potassium ( P<0.01 ) .The fluorescence in WT group was signifi-cantly higher than that in MT group (P<0.01).Western blot showed that mutant HERG protein included only one 60 kD band, different from the 135 kD and 155 kD bands in wild-type HERG, which were affected by the changes of extracellular potassium (P<0.05).CONCLUSION:The retention of HERG mutant L539fs/47 protein in the cytoplasm is more than wild-type HERG.Chronic high extracellular potassium keeps the stability of wild-type and mutant HERG proteins on the cell membrane.Chronic low potassium reduces the expression of HERG channel proteins in a time-dependent manner.