A stable calcium gradient near the plasma membrane

The influx of calcium ions from extracellular space plays a central role in regulation of function of living cells. It has been hypothesized that calcium influx causes a rise in intracellular calcium concentration ([Ca²⁺]_i) near the plasma membrane, thereby facilitating regulation of membrane associated processes without flooding the cell with Ca²⁺. Such a localization is extremely important, since high [Ca²⁺]_i is toxic to cells. However, existence of sustained areas of different Ca²⁺ concentrations within a continuous aquatic medium is not a trivial phenomenon. The mathematical model presented here evaluates the cytosolic concentration of Ca²⁺ as a function of time and distance from the plasma membrane. The model has verified quantitatively the feasibility of a stable Ca²⁺ gradient in the cytosol with high values of Ca²⁺ concentration near the plasma membrane and evaluated its properties as a function of different cellular parameters. The formation of the gradient does not required special distribution of the intracellular contents, channels and pumps. However, it requires buffering of the cytosolic calcium by the intracellular stores and that the rate of calcium release from the stores near the plasma membrane be higher than in other parts of the cell. We suggest that this model can provide an adequate description of the elevated calcium plateau generally observed in electrically non-excitable cells.