Your two equations are really the same one, as can be seen by canceling a proton from each side of equation 2. The reduced form of NAD, which is NADH, does not carry a second proton, not having any group with an appropriate pKa. (I would include a negative sign on the electron, but I am not sure that everyone would.) How is intracellular pH maintained? Is the cytoplasm buffered in any way?