Zn²⁺ slows the recovery from desensitization of the GABA_ARs. A, GABA (1 mm) (▪), 1 mm GABA plus 30 μm Zn²⁺ (▴), and 30 μmGABA (⬡) were applied to the same nucleated patch. Zn²⁺ was applied before and together with the agonist. Although the current responses to 1 mm GABA with and without Zn²⁺ showed almost identical rise times, 30 μm GABA had a much slower onset. All three current responses had different decay kinetics: 1 mm GABA decayed biexponentially, 30 μm GABA decayed monoexponentially, and 1 mm GABA plus 30 μmZn²⁺ showed a much faster decay of the slow component in comparison to control. The response to 30 μmGABA showed differences between desensitization and deactivation kinetics. The recovery from desensitization was studied with a protocol of two 20 msec pulses with variable interpulse intervals. Current traces with 300, 1000, and 5000 msec interpulse intervals are shown.B, The extent of recovery from desensitization was obtained from the amplitude ratio of the second pulse divided by the first (I₂/I₁) (also see Fig. 1C). The ratio obtained from four nucleated patches was plotted semilogarithmically against the interpulse interval and fitted with a biexponential function. The different times needed to obtain half-maximal recovery are indicated bydashed lines for the three conditions. ▪, 1 mm GABA; ▴, 1 mm GABA plus 30 μm Zn²⁺; ⬡, 30 μmGABA.