Dependence of I-Ks biophysical properties on the expression system

The delayed rectifier potassium current I-Ks is important for repolarizatio n of the cardiac action potential. In heart I-Ks, is a heteromeric channel composed of KCNQ1 (KvLQT1) and minK (KCNE1, IsK). Here we show that the KCN Q1/minK interaction is influenced by the expression system. Co-expression o f KCNQ1 and minK in Xenopus oocytes resulted in potassium cur-rents compara ble to endogenous guinea pig cardiac I-Ks in terms of temperature dependenc y and activation kinetics. In contrast, heterologous expression of I-Ks in CHO cells revealed currents with a markedly different biophysical behavior. The sensitivity to the extracellular potassium concentration, temperature dependency and kinetics differ qualitatively. Potentially there is an endog enous component that affects I-Ks which does not appear in all expression s ystems.