tracellular intrinsic buffers:$$\frac{\partial u_{0}}{\partial t} = \frac{CA_{e} \cdot \left( {k_{h} \cdot u_{0} - k_{r} \cdot u_{0} \cdot u_{0}} \right) + k_{d} \cdot u_{00} - k_{p} \cdot u_{0} \cdot u_{0}