其实, 拿NA-K PUMP来做例子, 他是一个PROTEIN, 但是SERVE TWO FUNCTIONS, 一个是要ESTABLISH AND MENTAIN CHEMICAL POTENTIAL, ANOTHER IS FOR ELECTRICAL POTENTIAL.3 SODIUM IONS ARE PUMPPED OUT WHEN 2 POTASSIUM IONS ARE PUMPPED IN. SO BOTH CHEMICAL (NA OUTSIDE AND K INSIDE) AND ELECTRICAL (3-2) POTENTIAL ARE ALTERED. AND THERE ARE MANY OTHER PROTEINS, ION CHANNELS MAY FUNCTION AT THE SAME TIME FOR FINE TUNE OR SIGNALING. THEY MAY HELP IN ESTABLISHING ONE OR BOTH POTENTIALS. SO, IT IS NOT ABSOLUTE THAT ONE PROTEIN ONLY HAS ONE FUNCTION. AND IT IS SURE THAT MANY PROTEINS CONTRIBUTE TO ONE SAME FUNCTION.

but you used the term "diffuse" wrongly:). ions cannot diffuse through the membrane. "diffuse" means there are no facilitated channels needed and it means the substrate molecules cross the barrier spontaneously.

but this faciliated diffusion does not function to the maintenance and establish this potential. or I should say, it does contribute to the equilibrium of the ion concentration on two sides, but the sensing proteins which really function for potentials are not them.