The role of calcium binding proteins in signal transduction

This chapter discusses the role of calcium (Ca)-binding proteins in signal transduction. Measurement of the free intracellular calcium [Ca²⁺] within cells suggests that it is very low, of the order of 10–100 nM. This means that the vast majority of intracellular Ca is bound. Considering that the extracellular Ca concentration is about 1 mM (compared to 10 nM [Ca²⁺]_i) and that the interior of the cell is negatively charged there is a large electrochemical gradient driving Ca ions into the cell, however the relative impermeability of the plasma membrane to Ca ions prevents large movements of Ca ions across the plasma membrane. The Ca transient is controlled by the uptake and release of Ca across the three major membrane systems which border the cytoplasm—the plasma membrane, the inner mitochondria1 membrane, and the endoplasmic reticulum. Each membrane possesses distinctive transport mechanisms which act in concert to regulate and modulate intracellular Ca. Cellular signal transduction can be divided into two separate components: (1) the generation of an intracellular signal from an external event and (2) transduction of the intracellular signal into the physiological response of the cell.