Zn²⁺-induced stimulation and the role of ultraslow inactivation gating. (A) Time course and degree of stimulation (top) and suppression (bottom) during application of 5.4 µM free Zn²⁺ at different holding potentials after separation of the opposing effects as described in the text (same cells as in Fig. 5). (B) Comparison of the relative Zn²⁺-induced increase of currents at 10 mV determined from the data in Fig. 2 F (i.e., after 2-s prepulses at the indicated test potentials, open squares) or A (i.e., 240 s after addition of Zn²⁺ at the indicated holding potentials, black squares). (C) Slow holding potential–dependent recovery from and development of inactivation induced by switching the holding potential from −60 mV to −70 mV and back to −60 mV in the absence of trace metal ions (n = 3 cells). (D) Comparison of time constants determined by exponential fits to the development of Zn²⁺-induced stimulation at a holding potential of −60 mV in A (Zn²⁺, orange) or to the recovery from holding potential-dependent inactivation in C (USI, black). (E) Comparison of the magnitude of current increase during Zn²⁺-induced stimulation at a holding potential of −60 mV (Zn²⁺, orange) and during recovery from holding potential–dependent inactivation (USI; black).