Why is the inside of a cell both more acidic and more negative than its environment?

In a very simplistic way of thinking, an acidic solution has more positively charged $\ce{H+}$ ions present, whereas a basic solution has more negatively charged $\ce{OH-}$ ions present.


Can that be simply reconciled with the fact that (1) the [intracellular pH](https://en.wikipedia.org/wiki/Intracellular_pH) of about 6.8 is more acidic than the intercellular pH of about 7.3, and that (2) a typical cellular [membrane potential](https://en.wikipedia.org/wiki/Membrane_potential) is -40 to -80 mV?




The key is that $\ce{H+}$ and $\ce{OH−}$ are not the only ions at play here. 


The selective permeability of different cellular membranes for different anions (i.e. $\ce{Cl−}$) and cations (i.e. $\ce{K+, Na+, Ca^{2+}, Mg^{2+},}$ etc.) results in charge separation. Cellular membrane potentials are thereby created, with or without an intercellular / intracellular pH gradient.


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