Fig. 4. Diffusional, ^DJ_H, and facilitated components, ^FJ_H, of total flux, ^TJ_H, are affected differently by increasing concentrations of the Good buffer MOPS.  An artificial source of protons approximately 1/10 the strength of the source in Fig. 3 is scanned with the same probe with different bathing buffer concentrations.  The percent of the proton current that is facilitated (% ^FJ) is plotted to demonstrate the increased proportion of facilitated diffusion within the range of the buffer and the increased error in estimating the total flux associated with high buffer concentrations. Flux is given in picomoles per cm² per sec.  The buffers used included: x µM MOPS, 100 µM KCl, 200 mM Sucrose.  The artificial source consisted of a capillary drawn to a 2 µm opening, filled with bath solution which lacked buffer, was adjusted to 0.001 N HCl and gelled with 0.08% agarose.