Fig. 12.

I_K(A) in pause–build neurons. K⁺ currents were recorded in saline containing 2 μm TTX. A, Isolation ofI_K(A). i, Bottom trace, The voltage-clamp protocol used to test for the presence of I_K(A). The cell was held at −60 mV and then prehyperpolarized to −100 mV for 500 msec, followed by a depolarization to −10 mV for 300 msec to evoke K⁺efflux and then returned to its holding potential. Top trace, K⁺ current evoked by this protocol. There was no measurable K⁺ current during the prehyperpolarizing step in this cell. ii, Bottom trace, Protocol used to inactivateI_K(A). The cell was held at −60 mV, predepolarized to −30 mV for 500 msec, followed by a depolarization to −10 mV, and then returned to its resting potential. Top trace, K⁺ current during the 300 msec depolarization to −10 mV. iii, The K⁺ current remaining after subtraction ofii from i shows the time course and magnitude of I_K(A) evoked during the voltage step to −10 mV. B, I_K(A)evoked by prehyperpolarizations of two different magnitudes; the larger prehyperpolarization evokes the largerI_K(A). Current traces shown are the subtracted traces resulting from a similar protocol to the one used inA, except that the prehyperpolarization was varied. In this cell, a small inward current is triggered by the larger hyperpolarizing step. C,I_K(A) has a monotonic dependence on the magnitude of the prehyperpolarization. D, Similar variation of pause time and I_K(A) with the magnitude of prehyperpolarization. E, Variation of pause time with peak I_K(A) amplitude. Data inC–E are the mean ± SEM of the same 11 cells.