Calcification mechanism

The final type of calcification mechanism involves some form of extracellular transport system which avoids all the transcellular energy barriers. As a concept, it is extremely valuable but it needs redefining of its relation to the ions under consideration and the motive forces for their movement. 

Calcification mechanisms. The mechanisms of CaCOs deposition have not been clearly defined. Two major questions are involved first, the relation of the organic portion of the skeleton to the initiation and control of crystal growth and, second, the role of the symbiotic photosynthetic zooxanthellae, the algae which grow within the tissue of hermatypic corals (Chapman, 1974). Another persistent question has been the site of crystal initiation, whether it is entirely extracellular or whether it is partly intracellulfir as well (Muscatine, 1971). 

Abedin M, Tintut Y, Demer LL (2004) Vascular calcification mechanisms and clinical ramifications. Arte-rioscler Thromb Vase Biol 24 1161-1170... 

Factors controlling calcium homeostasis are calcitonin, parathyroid hormone(PTH), and a vitamin D metabolite. Calcitonin, a polypeptide of 32 amino acid residues, mol wt - SGOO, is synthesized by the thyroid gland. Release is stimulated by small increases in blood Ca " concentration. The sites of action of calcitonin are the bones and kidneys. Calcitonin increases bone calcification, thereby inhibiting resorption. In the kidney, it inhibits Ca " reabsorption and increases Ca " excretion in urine. Calcitonin operates via a cyclic adenosine monophosphate (cAMP) mechanism. 

In contrast to the formation and calcification of bones, vitamin K seems to lower the risk of aortic calcification. The mechanisms for these antagonistic effects is not known but a participation of osteocalcin (expressed in artherosclerotic plaques) as well as of matrix Gla protein (MGP) are discussed. In addition, the vitamin K epoxide reductase complex seems to be involved [5]. 

Further work on ADH may identify the molecular mechanisms underlying the brain calcification and tonic-clonic seizures associated with the CASR-activating mutations. This information may refine therapy for ADH patients as well as hypoparathyroidism patients who harbor CASR mutations. Further details about ADH can be found in the CASR locus-specific database at http //www.casrdb. mcgill.ca/f4/). 

From this description it is clear that this new cell is a highly specialized feature and this rises an interesting question of what was the primary reason for development of such a cell in the fish, where bones are not resorbed and colonized by the hematopoiesis. There is no experimental answer to this question yet, but speculation on that subject should concentrate on other requirements for bone resorption that would be of an immediate necessity for the fish. Such other requirement is tooth eruption. Without teeth fish would be unable to eat most of the food available, and to defend itself, so their eruption is of critical importance for survival. With emergence of calcification of bones during their development teeth had it increasingly more difficult to erupt and this required development of mechanism to assist in this process. So the hypothesis based on this speculation is, that the osteoclasts emerged primarily to assist tooth eruption. 

T.A. Einhorn, G.K. Wakley, S. Linkhart, E.B. Rush, S. Maloney, E. Faierman, D. J. Baylink, Incorporation of sodium fluoride into cortical bone does not impair the mechanical properties of the appendicular skeleton in rats, Calcif. Tissue Int. 51 (1992) 127-131. 

Mechanism of Action A fat-soluble vitamin that is essential for absorption, utilization of calcium phosphate, and normal calcification of bone. Therapeutic Effect Stimulates calcium and phosphate absorption from small intestine, promotes secretion of calcium from bone to blood, promotes renal tubule phosphate resorption, acts on bone cells to stimulate skeletal growth and on parathyroid gland to suppress hormone synthesis and secretion. 

For nearly half a century the elastic fibre has been considered a primary site of vascular calcification326, 334 336), Calcium deposits in the arterial wall commonly take the form of phosphate salts which are intimately intermeshed with the protein of the elastic fibre327. Much effort has been directed toward identifying the mechanism for the initiation of focal calcification. It has been proposed that the initial step is ionic calcium binding to the uncharged peptide carbonyl oxygens of the elastic fibre protein328, 329. ... 

Vogel, J. J., Boyan-Salyers, B. D. Acidic lipids associated with the local mechanism of calcification. A review. Clin. Orthop. 118, 230 (1976)... 

Krampitz, G., Engels, J., Hamm, M., Kriesten, K., Cazaux, C. On the molecular mechanism of the biological calcification. 1. Ca-ligands from gastropod shells, egg-shells and uterine fluid of hens. Biomineralisation 9, 59 (1977)... 

De Jong, L. W., Dam, W., Westbroek, P., Crenshaw, M. A. Aspects of calcification in Emiliania huxleyi (unicellular alga). In The mechanisms of mineralization in the invertebrates and plants. Watabe, N. Wilbur, K. M. (eds.). The Belle W. Baruch Library in Marine Science Vol. 5, pp. 135. University South Carolina Press 1976... 

Digby, P. S. B. Calcification and its mechanisms in the shore crab Carcinus maenas. Proc. Linn. Soc. Lond. 178, 129 (1967)... 

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