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 of about 6.8 is more acidic than the intercellular pH of about 7.3, and that (2) a typical cellular membrane potential is -40 to -80 mV?