Sensing calcium

Recently, a chameleon calcium reporter has been designed by R.Y. Tsien to sense calcium in cells by FRET. The structure of the system is based on a CEP separated from an YEP by the calmodulin calcium binding protein (CaM) and a calmodulin binding peptide (M13). If Ca ions are bound, CaM wraps around Ml 3 allowing high efficiency of excitation transfer from the donor CEP to the acceptor YEP (see Figure 9). The degree of FRET in chameleon is a sensitive ratiometric reporter (ratio 527/434 YPE/ CEP) of the calcium concentration in cells and in solution. The beauty of this approach is that the... 

Kuhla, B., D. Albrecht, S. Kuhla and C.C. Metges, 2009. Proteome analysis of fatty liver in feed deprived dairy cows reveals interaction of fuel sensing, calcium, fatty acid and glycogen metabolism. Physiol Genomics 37, 88-98. Eymann, C., D. Becher, J. Bernhardt, K. Gronau, A Klutzny and M. flecker, 2007. Dynamics of protein phosphorylation on Ser/Thr/Tyr in Bacillus subtilis. Proteomics 7, 3509-3526. 

When a metal such as sodium (Na) or calcium (Ca) reacts with a nonmetal such as chlorine (Cl2), the product is ordinarily an ionic compound. The formula of that compound (e.g., NaCl, CaCl2) shows the simplest ratio between cation and anion (one Na+ ion for one Cl ion one Ca2+ ion for two Cl- ions). In that sense, the formulas of ionic compounds are simplest formulas. Notice that the symbol of the metal (Na, Ca) always appears first in the formula, followed by that of the nonmetal. 

Ca2+ sensing receptor, a member of G-protein coupled receptors, is composed of seven transmembrane spanning domains. The extracellular domain contains clusters of negatively charged amino acids sensing even small fluctuations of extracellular calcium. Mutations in this receptor cause inheritable hypo- and hypercalcemic syndromes. 

Calcium receptor Extracellular calcium-sensing receptor (CaSR)... 

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)... 

Hofer AM, Brown EM (2003) Extracellular calcium sensing and signalling. Nat Rev Mol Cell Biol 4 530-538... 

Tfelt-Hansen J, Brown EM (2005) The calcium-sensing receptor in normal physiology and pathophysiology a review. Crit Rev Clin Lab Sci 42(1 ) 3 5-70... 

A class of allosteric activators of the Ca2+-sensing receptor that sensitizes the receptor to extracellular calcium and acts only in the presence but not in the absence of calcium. Calcimimetics can be used to treat various forms of hyperparathyroidism, although they are only approved for use in patients with end stage renal disease receiving dialysis treatment. 

Calcium channels in the plasma membrane activated after receptor-mediated calcium release from intracellular stores. Diese channels are present in many cellular types and play pivotal roles in a multitude of cell functions. It was recently shown that Orai proteins are the pore-forming subunit of CRAC channels. They are activated by STIM proteins that sense the Ca2+ content of the endoplasmic reticulum. 

Extracellular Calcium-sensing Receptor (CaSR) Extracellular Matrix (ECM)... 

In contradistinction to site-specific molecules there are other toxins which, in a sense, create their own specificity. Thus ionophore toxins, by opening up the cell membrane to sodium and calcium ions, create their own specificity. Prime examples of this are found in cytolytic toxins in general, and jellyfish toxins and palytoxin in particular. 

Because of their strategic localization, astrocytes play a crucial role in maintaining the extracellular ionic homeostasis, provide energetic metabolites to neurons and remove excess of neurotransmitter in schedule with synaptic activity. In addition, the strategic location of astrocytes allows them to carefully monitor and control the level of synaptic activity. Indeed, number of papers during the last 15 years have shown that cultured astrocytes can respond to a variety of neurotransmitters with a variety of different patterns of intracellular calcium increases (Verkhratsky et al. 1998). Later on, studies performed in intact tissue preparations (acute brain slices) further established that the plasma membrane receptors can sense external inputs (such as the spillover of neurotransmitters during intense synaptic activity) and transduce them as intracellular calcium elevations, mostly via release of calcium from internal stores (Dani et al. 1992 Murphy et al. 1993 Porter and McCarthy... 

Novel external/internal sensing and signalling systems, often based on calcium gradients,... 

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