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. 2013 Oct;142(4):381–404. doi: 10.1085/jgp.201311015

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© 2013 Vocke et al.

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Figure 2. — Cl⁻ depletion and the initial, rapid current decline. (A and B) Current traces at different Ca²⁺ concentrations demonstrate that larger currents cause faster current decline. Inset, current-to-voltage (I/V_m) relations obtained from −80 mV to +80 mV voltage ramps (duration, 1 s). The first ramp was applied 2 min after whole-cell (wh.c.) breakthrough. The initial currents transient lasted 28 s and reached −6.5 nA peak amplitude at −70 mV. Repeated voltage ramps at 15-s intervals caused a progressive shift of the reversal voltage from −29 mV toward 0 mV, indicating a rising intracellular Cl⁻ level caused by Cl⁻ influx during the ramp protocol. (C) The current integral (blue) calculated from the initial Cl⁻ current (−I(t); red), indicates the charge transfer accumulated during the rapid current transient. The current integral was used to estimate changes of intracellular Cl⁻ concentration, Δc, according to Δc = ΔQ/(V × e × L), where Q indicates the measured accumulated charge, V = 0.5 pL an assumed cell volume, e the elementary charge, and L the Avogadro constant. (D) Current recording depicting the parameters that characterize the current decline: maximal current, I_max; time for 80% of current decline, t_off; total extent of current decline, ΔI. (E) The speed of current decline depends on the pipette Ca²⁺ concentration and is faster in ANO 1 than in ANO 2. (F) The total extent of current decline does not depend on Ca²⁺ concentration. Error bars indicate mean ± SEM. (G) Whole-cell recordings from four different cells that express ANO 1 illustrate that the rapid decline of the initial current is observed at negative voltages, but not at +40 mV. The arrow indicate whole cell breakthrough.