Membrane currents were recorded using the tight-seal, whole-cell patch recording configuration. The extracellular solution contained 130 mM NaCl, 5.5 mM KCl, 2.2 mM CaCl2, 1 mM MgCl2, and 10 mM HEPES, pH adjusted to 7.4 with NaOH. The pipette solution contained 139 mM KCl, 1 mM MgCl2, 10 mM HEPES, 3 mM Na2ATP, and 0.05 mM fluo-3, pH adjusted to 7.3 with KOH. For experiments in Fig. 8, 40 mM NaCl was replaced by 40 mM KCl to set Ek at −28 mV, and niflumic acid at 50 µM was added to block the STICs (Hogg et al., 1994; Janssen and Sims, 1994). Whole-cell currents were recorded at a holding potential of 0 mV, low-pass filtered using the Axopatch 1D amplifier (Molecular Devices; 200-Hz cutoff), and then digitally sampled at 1 kHz and stored for analysis. Events were counted as STOCs if they exceeded a threshold of 10 pA as detected by Mini analysis software (Synaptosoft, Inc.). The events were then visually inspected to eliminate anomalies such as multiple events overlapping in time or excessively noisy traces.
