Fig. 7. Blockage of Cl^- currents reveals a second voltage dependent current. (Ai) In a bath containing 0 Cl^- and 0 Ca²⁺, slow outward voltage dependent currents persist (shadow, a representative trace from a different cell in ASW at +63 mV). The activation curve of the currents can be fit successfully with a Boltzman function (Aii) (correlation=0.949, N=7). The high K value equates roughly to 1.2 charges, assuming the simple open-close model for channel activation. Fast I-V (Aiii) shows 0 Cl^-, 0 Ca²⁺ bath (triangles) removes completely the fast Cl^- current component (compared to ASW bath, circles), leaving only the slow activating putative H⁺ current. The currents are very sensitive to the application of zinc. (B) The currents from a representative cell before (Bi) and after (Bii) the application of 10 µmol l^-1 ZnCl₂. A slow I-V plot (Biii) shows that amplitudes at all voltages are dramatically reduced in the presence of ZnCl₂ (N=7). Finally, decreasing pH causes a reduction in current amplitude and a shift in the current reversal potential. (Ci) Currents from a representative cell show a decrease in amplitude in the lower 7.0 pH and (Cii) a plot of the shift in reversal potential E_rev from the same cell shows a shift of +52 mV. The mean shift measured was +51.867±6.7 mV (N=5), very close to the predicted +56 mV shift.