I am getting about a 0.5nA outward current in untransfected i.e. wild type CHO cells at 40mV. This makes it difficult to interpret the effects of inhibitors on cells transfected with known potassium channels, such as KvLQT1. Some literature suggests there are no functional potassium channels in wild type CHO and HEK cells although Frasermoss recently indicated some HEK cells have endogenous channels. Is there a way to get rid of this background? It is not inhibited by TEA or 4-AP, i.e. standard potassium channel inhibitors. Am using perforated whole cell voltage clamp on an IonworksHT, and regular HEPES-buffered internal and external solutions. Suggestions?