Channels, versus carriers

In a discussion of permeability it is important to recognize that we deal with operational definitions, since the act of measurement influences the state of the system. In your case, applying an electrical potential gradient and performing electrodialysis alter the distribution of ionophore within the membrane. I wonder whether you have attempted to measure permeability by isotopic tracer techniques In this method the distribution of ionophore would not be influenced. Furthermore, information can be obtained on the question of carriers versus channels or pores. It should not be difficult to determine the extent of possible isotope interaction between tracer species and abundant species in the membrane as discussed by Kedem and Essig [J. Gen. Physiol., 48, 1047 (1965)]. Positive isotope interaction would tend to suggest the presence of channels or pores, negative isotope interaction the presence of carriers. 

FIGURE 6.2 Height equivalent to a theoretical plate (H) of a GC-separated compound versus average carrier gas velocity for a 3-m-long silicon channel coated with non-polar dimethyl polysiloxane stationary phase (a) native silicon surface (b) oxidized silicon surface. Plots A are for hydrogen carrier gas, and plots B are for air carrier gas [598]. Reprinted with permission from the American Chemical Society. 

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