(color online) Typical models of current signal curves at the initial stage. The current signals in panels (d), (e), and (f) are the reversal response of panels (a), (b), and (c), respectively. [(a) and (b)]: A typical exponential decay of I, where 0.05-M KCl, external voltage is 100 mV, 20 mV, respectively, pH = 7, the channel diameter is . (c): A typical oscillating decay of I, where 0.2-M KCl, at 25 mV, and pH = 7, . [(d) and (e)]: A typical exponential decay of , where 0.05-M KCl, external voltage is 200 mV, 300 mV, respectively, and pH = 7, . (f): A tyical oscillating decay of , where 0.2-M KCl, external voltage is 20 mV, pH = 7, .