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What is the function of the membrane potential? Cells invest huge amounts of ATP to drive ion pumps to sustain this potential. Therefore it must have a very important function.

I read somewhere that the membrane potential acts as a battery, which can be used to energize other processes. But probably most of these processes could be energized with ATP just as well, which could be used directly instead of wasting it into building a potential first.

In muscle cells and nerve cells changes in the membrane potential are used to transmit information, so that is one use for it. But what about all the other cells?