Calcium buffering describes the processes which help stabilise the concentration of free calcium ions within cells, in a similar manner to how pH buffers maintain a stable concentration of hydrogen ions. The majority of calcium ions within the cell are bound to intracellular proteins, leaving a minority freely dissociated. When calcium is added to or removed from the cytoplasm by transport across the

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

or sarcoplasmic reticulum, calcium buffers minimise the effect on changes in cytoplasmic free calcium concentration by binding calcium to or releasing calcium from intracellular proteins. As a result, 99% of the calcium added to the cytosol of a cardiomyocyte during each cardiac cycle becomes bound to calcium buffers, creating a relatively small change in free calcium. The regulation of free calcium is of particular importance in excitable cells like cardiomyocytes and

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s. Within these cells, many intracellular proteins can act as calcium buffers. In cardiac muscle cells, the most important buffers within the cytoplasm include troponin C, SERCA, calmodulin, and

myosin Myosins () are a Protein family, family of motor proteins (though most often protein complexes) best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are adenosine triphosphate, ATP- ...

, while the most important within calcium buffer within the sarcoplasmic reticulum is calsequestrin., The effects of calcium buffers depends on their affinity for calcium, as well as the speed with which they bind and release it.

Clinical significance

Alterations in calcium buffering within the cytosol have been implicated in the tendency to arrhythmias (abnormal cardiac rhythms) in some genetic mutations known to cause hypertrophic cardiomyopathy. Genetic mutations affecting calsequestrin are responsible for an

autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

form of catecholaminergic polymorphic ventricular tachycardia, an inherited cardiac condition that can lead to sudden death. Calcium buffering within atrial myocytes is affected by ageing in large animal models, elevating sarcoplasmic reticulum calcium content, which could potentially contribute towards a tendency to

atrial fibrillation Atrial fibrillation (AF, AFib or A-fib) is an Heart arrhythmia, abnormal heart rhythm (arrhythmia) characterized by fibrillation, rapid and irregular beating of the Atrium (heart), atrial chambers of the heart. It often begins as short periods ...

References

{{Reflist Calcium signaling

Clinical significance

See also

References