Figure 9.

ATP permeability of large-conductance anion channel recorded from inside-out patches excised from C127i cells. Currents were recorded in standard Ringer's bath solution or in a 100 mM Na₂ATP bath solution. (A) Representative ramp I-V records from a macro-patch in the absence and presence of 100 mM ATP in the bath. Pipette solution was standard Ringer's. (B) Single-channel i-V relationships in the presence of 100 mM ATP in the bath. Solid line represents ramp i-V, recorded using standard Ringer's as the pipette solution. Open circles and triangles represent the mean ± SEM of 4–21 single-channel currents measured upon application of step pulses at voltages indicated on the abscissa using standard Ringer's and TEA solutions, respectively, as the pipette solution. The SEM values are shown by vertical bars where the values exceed the symbol size. (C) One and three representative traces of single-channel currents recorded at +50 and −50 mV, respectively, in the presence of 100 mM ATP in the bath. The pipette solution was standard Ringer. Dashed lines indicate zero-current level. (D) Amplitude histograms of single-channel currents recorded at ±50 mV. For outward Cl⁻ currents at +50 mV, peaks correspond to unitary steps of 10.3 ± 1.9 and 10.7 ± 3.2 pA together with a sublevel at ∼6.7 pA. For inward ATP⁴− currents at −50 mV, two peaks corresponding to unitary steps of −1.7 ± 1.1 and −1.4 ± 0.8 pA can be distinguished.