Influx of Ca2 from the Extracellular Region

In the extracellular region, the Ca2+ concentration is over 10-3 M, which is very high in comparison to the free cytosolic Ca2+ concentration. The cell membrane contains a variety of different Ca2+ channel types that enable Ca2+ influx to take place from the extracellular region into the cytosol. One of the primary functions of Ca2+ entry is to charge up the internal stores, which can then release an internal Ca2+ signal. 

In addition we know of Ca2+ channels that are controlled by Ga proteins (see Section 5.5.1) and Ca2+ channels that are gated by sphingolipids. 

Opening of Ca2+ leads to a local increase in the cytosolic Ca2+ concentration from 10 7 M to 10 6 M. In this concentration region, the Ca2+ transport systems mentioned above work very efficiently. However, if an increase in Ca2+ concentration over 10 5 M takes place, e. g., because of cell damage, a level critical for the cell is reached. In this case, Ca2+ is pumped into the mitochondria with the help of Ca2+ transport systems localized in the inner membrane of the mitochondrion. 

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