The Importance Of Calcium Ions

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Calcium ions are vital for cellular signalling, as once they enter the cytoplasm they use allosteric effects caused by indirect transduction pathways such as G protein-coupled receptors. Calcium signalling is cause by gradients across the plasma membrane, as the resting concentration of Ca2+ in the cytoplasm is normally kept ˷100 nM, compared to the extracellular concentration which is ˷1.5mM. To continue low concentration within the cell, Ca2+ signals can be generated either from extracellular calcium or from within the intracellular stores. Some proteins within the cell act as sensors and buffers to ensure that the concentration remains within its range and does not rise above 10x-7M that can cause cell death.
When cells are stimulated, the
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Ca2+ ions are transported out of the cell or back into the Ca 2+ rich organelles. This is against an electrochemical gradient, and thus requires energy. Calcium is removed from cells by two basic mechanisms. The first mechanism involves an ATP-dependent Ca2+ pump that actively removes calcium from the cell. The second mechanism is the sodium-calcium exchanger (NCX). These pumps and exchangers operate at different times during the recovery process. The Na+/Ca2+ exchangers have low affinities for Ca2+ but have very high capacities. At the start of the recovery process, it rapidly removes large amounts of Ca2+ from the cell as is needed after an action potential. This exchanger can move Ca2+either into or out of cells, depending on the force. The NCX removes one calcium ion in exchange for the import of three sodium ions into the cell. On the other hand, the plasma membrane Ca2+ATPase (PMCA) and Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pumps have lower capacities, but higher affinity which mean that they can complete the recovery process and can continue to pump less Ca2+, therefore allows them to maintain the resting level and internal stores. NCX exchanger is involved in abnormality of the cardiac electrical conduction called delayed afterdepolarization as an …show more content…
The Calcium sensors respond to changes in intracellular Ca2 + by activating effector process whereas Ca2+ buffers ensure that the concentration of Ca2 + remains within its range and levels do not rise above the threshold therefore involved in the regulation of signalling and homoeostasis. Ca2+ buffers are important in shaping both the spatial and temporal properties of Ca2 + signals such as paralbumins, calbindin-D9k, calbindin-D28k, and calretinin. Firstly, Calreticulin is a low-affinity Ca2 + -binding protein that is found within the lumen of the ER. Calreticulin ensures that the Ca2 + concentration within the ER are maintained at the optimal level for protein folding to occur. Secondly, Parvalbumin is a slow-onset buffer as it cannot respond to the rapid onset of most Ca2 + signals. However, once activated it can take up high calcium levels. It is mainly in skeletal muscle and involves in muscle relaxation. Furthermore, Calbindin D-28 is important in processes in the spine, allowing faster communication between neurones. However low level causes increase sensitivity to neurones. Finally, calretinin is found in the cytoplasm it acts as a biochemical marker for certain GABAergic inhibitory interneurons to control the micro domains of calcium.

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