Calcium messages 350

In essence the above devices are just rearrangements of helices to open channels and/or to transmit energy. They are therefore applicable as models to all the agonist receptor systems which cause either the input of a calcium message or the formation of c-AMP from ATP. The last reaction is a special type of ATP-ase since it is a downhill use of ATP. Acetylcholine binding can be relayed to the opening of helical channels or to ATP reactions through helix movements. 

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 chemistry of such an experience is now quite well understood. Capsaicin interacts with a specific protein, a receptor, on the surface of nerve cells and triggers an influx of calcium into the cell. This then liberates a string of amino acids, known as substance P, from nerve endings. These send the pain message to the brain. And that pain can be intense. 

The message of calcium is conveyed from the troponin to which it binds, via tropomyosin to the actin filament193-198).As soon as the nerve impulse ceases, the calcium becomes quickly removed and returned to the storage sites situated in the membranes of the sarcoplasmic reticulum. When Ca2+ concentration in the sarcoplasm reaches 1 x 10-7 molar, the fiber is relaxed. 

Boon, N., Hul, G. B., Viguerie, N., Sicard, A., Langin, D., and Saris, W. H. (2005). Effects of 3 diets with various calcium contents on 24-h energy expenditure, fat oxidation, and adipose tissue message RNA expression of lipid metabolism-related proteins. Am. ]. Clin. Nutr. 82,1244-1252. 

The following effects take place because the receptors are coupled to adenylyl cyclase or to phospholipase C. Adenylyl cydase catalyzes the synthesis of cAMP, while phospholipase C catalyzes the hydrolysis of the phosphahdy -4,5-bisphos-phate, releasing inositol-1,4,5-trisphosphate (11 3). This IP3, in turn, travels to the endoplasmic reticulum, where it provokes the momentary release of calcium ions. The increase in ion levels, in turn, provokes activation of a number of protein kinases, as discussed in the Calcium and Phosphate seebon. All of these receptors are p(dypeptides that weave seven times in or out of the plasma membrane. All of these receptors are directly linked to G protein, and require G protein for transmitting their message within the membrane to various enzymes. 

Both calcium-45 and calcium-47 can be used to study how calcium is used in the body. A doctor may think that a person s body is not using calcium properly in making bones or regulating nerve messages. The doctor can use calcium-45 or calcium-47 to find out more about this problem. The radioactive isotope is injected into the person s bloodstream. Then its path can be followed by the radiation it gives off The doctor can then tell if the calcium is being used normally in the body. 

The k receptor is directly associated with a calcium channel (Fig. 12.42). When an agonist binds to the k receptor, the receptor changes conformation and the calcium channel (normally open when the nerve is firing and passing on pain messages) is closed. Calcium is required for the production of the nerves neurotransmitters and therefore the nerve is shut down and cannot pass on pain messages. 

Doubly ionized calcium (Ca2+) delivers information about the stars, about processes in Earths oceans, and even about how the human brain sends messages through the central nervous system. Because the ions carry excess charge, they move in response to changing voltages. When a neuron fires in the brain, it instantaneously changes the electric poten-... 

This response in the muscle to calcium, which increases during contraction, allows for individual, active muscles to increase glycogenolysis without necessitating the hormonal message, epinephrine, which would affect all muscles. 

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