Calcium intracellular concentration regulation

There is a significant difference between the Ca2+ concentrations of intracellular (0.01 mM) and extracellular fluids (2.5 mM). The calcium ion is one of the most disruptive substances for normal cell function, with the intracellular concentration of calcium ions carefully regulated (Saul, 2009) and bone matter serving as the major storage sites for excess calcium. 

In the central nervous system, calcium is implicated in the regulation of membrane excitability, neurotransmitter release, axonal transport, dendrite morphology and regulation of numerous enzymatic reactions. Intracellular concentration of free calcium must be precisely regulated to maintain a strong Ca" " gradient between the cytoplasm (lO M) and the extracellular space (lO M). 

Although the major part of the body s calcium is in bones, the most important functions of calcium are in the maintenance of muscle contractility and responses to hormones and neurotransmitters. To maintain these essential regulatory functions, bone calcium is mobilized in deficiency, so as to ensure that the plasma and intracellular concentrations are kept within a strictly controlled range. If the plasma concentration of calcium falls, neuromuscular regulation is lost, leading to tetany. 

Regulation of Intracellular Free Calcium Concentration (an n-Compartment System) 183... 

Once the intracellular Ca " concentration begins to rise, calmodulin-calcium binding also rises and MLCK, which is dependent on calmodulin activation, rises in turn. The next step in this cascade is the phosphorylation of myosin. Finally, the phosphorylation of myosin results in the activation of the crossbridges and the accompanying transduction of ATP energy into mechanical work. Despite its differences in regulation, smooth muscle behaves mechanically much like other muscles. 

The sarcolemmal Na/K pump plays an imp>ortant, although indirect role in the regulation of cellular calcium homeostasis. The transmembrane Na gradient is maintained by the activity of the Na/K pump and the thermodynamic energy of this gradient in turn drives the Na/Ca exchange mechanism (Sheu and Fozzard, 1982 Barry and Bridge, 1993). Thus, the intracellular Ca concentration is closely related to intracellular Na and the activity of the Na/K pump (Bers and Ellis, 1982). 

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