KV 1.3 currents recorded from Jurkat cells and block by Cs⁺. Top panel shows currents elicited by a voltage step from -80 to +40mV for 200ms, subsequent block of the current by internal perfusion of Cs⁺, and recovery after washout of Cs⁺. Internal solution replacement was repeated 19 times and the recording was stable for over 35 minutes.