Calcium buffering

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.[1] The majority of calcium ions within the cell are bound to intracellular proteins, leaving a minority freely dissociated.[2] When calcium is added to or removed from the cytoplasm by transport across the cell membrane 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.[2]

The regulation of free calcium is of particular importance in excitable cells like cardiomyocytes[3] and neurons.[4] 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, while the most important within calcium buffer within the sarcoplasmic reticulum is calsequestrin.[2][5]

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.[6] Genetic mutations affecting calsequestrin are responsible for an autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia, an inherited cardiac condition that can lead to sudden death.[7] 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.[8]

See also

References
  1. Gilabert JA (2012). "Cytoplasmic calcium buffering". Advances in Experimental Medicine and Biology. Advances in Experimental Medicine and Biology. 740: 483–98. doi:10.1007/978-94-007-2888-2_20. ISBN 978-94-007-2887-5. PMID 22453955.
  2. M., Bers, D. (2001). Excitation-contraction coupling and cardiac contractile force (2nd ed.). Dordrecht: Kluwer Academic Publishers. ISBN 9780792371588. OCLC 47659382.
  3. Smith GL, Eisner DA (May 2019). "Calcium Buffering in the Heart in Health and Disease". Circulation. 139 (20): 2358–2371. doi:10.1161/CIRCULATIONAHA.118.039329. PMC 6520234. PMID 31082292.
  4. Schwaller B (November 2010). "Cytosolic Ca2+ buffers". Cold Spring Harbor Perspectives in Biology. 2 (11): a004051. doi:10.1101/cshperspect.a004051. PMC 2964180. PMID 20943758.
  5. Briston SJ, Dibb KM, Solaro RJ, Eisner DA, Trafford AW (November 2014). "Balanced changes in Ca buffering by SERCA and troponin contribute to Ca handling during β-adrenergic stimulation in cardiac myocytes". Cardiovascular Research. 104 (2): 347–54. doi:10.1093/cvr/cvu201. PMC 4240166. PMID 25183792.
  6. Schober T, Huke S, Venkataraman R, Gryshchenko O, Kryshtal D, Hwang HS, Baudenbacher FJ, Knollmann BC (July 2012). "Myofilament Ca sensitization increases cytosolic Ca binding affinity, alters intracellular Ca homeostasis, and causes pause-dependent Ca-triggered arrhythmia". Circulation Research. 111 (2): 170–9. doi:10.1161/CIRCRESAHA.112.270041. PMC 3393041. PMID 22647877.
  7. Lieve KV, van der Werf C, Wilde AA (May 2016). "Catecholaminergic Polymorphic Ventricular Tachycardia". Circulation Journal. 80 (6): 1285–91. doi:10.1253/circj.CJ-16-0326. PMID 27180891.
  8. Clarke JD, Caldwell JL, Pearman CM, Eisner DA, Trafford AW, Dibb KM (October 2017). "2+ handling in old sheep atrial myocytes". The Journal of Physiology. 595 (19): 6263–6279. doi:10.1113/JP274053. PMC 5621500. PMID 28752958.
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