Calcium ions, role

Calcium ion plays an important role in many aqueous environmental systems. A useful direct analysis takes advantage of its reaction with the ligand ethylenedi-aminetetraacetic acid (EDTA), which we will represent as... 

The extracellular calcium Ca -sensing receptor plays a central role in maintaining a nearly constant level of extracellular calcium by sensing small changes in Ca and directly and/or indirectly altering the translocation of calcium ions into or out of the extracellular fluid so as to normalize CaQ+. Changes in the level of expression and/or function of the CaR reset the level of CaQ+. Recently developed activators (calcimimetics)... 

Bellomo, G., Richelmi, P., Hirabelli, F., Marioni, V. and Abbagnano, A. (1985). Inhibition of liver microsomal calcium ion sequestration by oxidative stress role of protein sul-phydryl groups. In Free Radicals in Liver Injury (eds. G. Poli, K.H. Cheeseman, M.U. Dianzani, and T.F. Slater) pp. 139-142. IRL Press, Oxford. 

Morgan JM, Navabi H, Schmid KW, et al. Possible role of tissue-bound calcium ions in citrate-mediated high-temperature antigen retrieval. /. Pathol. 1994 174 301-307. 

Now described as a trp superfamily, more than 20 vertebrate trp homologs have been identified and these can be divided phylogenetically into three subfamilies trpC (termed canonical as they are most closely related to Drosophila trp), trpV and trpM. Some of these proteins are potential contenders for the capacitative calcium ion entry channel. In particular, expression of members of the TRPC and TRPV families in mammalian cells has been shown to augment capacitative calcium ion entry, but their role is still a matter for debate [17]. 

Calcium ions play a critical role in regulating the synthesis and release of neurotransmitters, in neuronal excitability, and in long-term neuroplastic events, and it is thus not surprising that a number of studies have investigated intracellular Ca2+ in peripheral cells, particularly in bipolar disorder. 

Matsumoto M, Inagaki M, Kiuchi Y, et al. 1993. Role of calcium ions in dopamine release induced by sodium cyanide perfusion in rat striatum. Neuropharmacol 32(7) 681-688. 

In addition to the displacement of caldesmon, smooth muscle cell contraction requires kinase-induced phosphorylation of myosin. Smooth muscle has a unique type of myosin filament called p-light chains which are the target (substrate) for MLCK, but MLCK is only active when complexed with CaCM. Myosin light chain phosphatase reverses the PKA-mediated process and when cytosolic calcium ion concentration falls, CDM is released from CaCM and re-associates with the actin. The central role of calcium-calmodulin in smooth muscle contraction is shown in Figure 7.4. 

The CD spectrum of this peptide in 0.2 M NaCl showed no significant difference from that of the Ca2+-free solution above. The results support the conclusion that calcium ions play a specific role in the conformation of this peptide fragment. 

Calmodulin This low-molecular-weight protein appears to depolymetize mkrotubules in the presence of calcium ion, but its exact role is unclear due to conflicting assertions about whether its action is directed toward tubulin and/or toward microtubule-associated proteins (Kakiuchi, 1982 Kumagai et aL, 1982 Lee and Wolff, 1982)... 

This group or complex of proteins may be isolated from cold-staUe microtubules. Their ability to stabilize microtubules appears to be diminished by the comUned action of calcium ion and calmodulin (Job et al., 1983). The role in controlling or affecting microtubule stability at physiological temperatures remains to be established... 

In addition to its structural role in bone, and in teeth, the calcium ion is a carrier of chemical messages. It influences secretion, contraction of muscle, cell division, growth, transcription, as well as other key physiological processes. 

The calcium ion is a key factor in human nutrition. It has an important structural role in bone and teeth and is a regulatory factor in many aspects of metabolism. 

Recently there has been much interest in the possible role of the family of protein kinases which translate information from the second messenger to the membrane proteins. Many of these kinases are controlled by free calcium ions within the cell. It is now established that some serotonin (5-HT) receptors, for example, are linked via G proteins to the phosphatidyl inositol pathway which, by mobilizing membrane-bound diacylglycerol and free calcium ions, can activate a specific protein kinase C. This enzyme affects the concentration of calmodulin, a calcium sequestering protein that plays a key role in many intracellular processes. 

---