Ba²⁺ block in NaK2K. (A) Internal Ba²⁺ block in the presence and absence of external K⁺. The nonconducting dwell time histograms with exponential fits for each recording are shown beside each trace. Only the patch that contains a channel with its intracellular side facing the bath solution was used in the recording. (B) External Ba²⁺ block in the presence of 5 mM external K⁺. Only the patch that contains a channel with its extracellular side facing the bath solution was used in the recording.