Comparison of NaCl, Na(Mg)ATP, and NaADP diffusion in gelatin using conductance measurements to monitor diffusion. (A) NaCl (40 mM) was applied and removed, followed by Na(Mg)ATP (40 mM) and then NaCl again. The gray curve is a simulation for a Na-anion pair in which the anion diffuses 10 times slower than Cl. Similar to the simulation, the conductance record for 40 mM Na(Mg)ATP rises in a biphasic fashion and declines more than three times slower than the records for NaCl. (B) NaADP diffusion into a gelatin-filled pipette tip follows a similar pattern to Na(Mg)ATP. (C) Comparison of NaCl and Na(Mg)ATP diffusion in pipette tips with 0, 6, and 12 g% gelatin. For all results, n ≥ 5. The decay constant for NaCl decreases by 25 and 41% in 6 and 12% gelatin, respectively, while the decay constant for Na(Mg)ATP is decreased by 80% in both gelatins. We mention that the results for NADH were similar. (D) Dependence of steady state conductances on the percent gelatin employed. Impressively, increasing concentrations of gelatin cause similar relative steady-state conductance changes. This is not unexpected, since MgATP contributes only about 20% of the conductance to the Na(Mg)ATP solution. A decrease of MgATP diffusibility can cause a large change of the coupled diffusion coefficient but only a small change of the steady-state conductance.