Messenger molecules

On the other hand, cNOS is continuously expressed in the ceils, and upon stimulation of the cell, the formation of NO begins immediately. However, the amounts of NO produced are minute. The nature of NO in cells expressing cNOS is only to act as a messenger molecule, whereas NO has also other functions in cells expressing iNOS. For example, NO has bacteria and cell killing properties in immunological cells, such as phagocytes. ... 

FIGURE 5.3 Different types of functional readouts of agonism. Receptors need not mediate cellular response but may demonstrate behaviors such as internalization into the cytoplasm of the cell (mechanism 1). Receptors can also interact with membrane proteins such as G-proteins (mechanism 2) and produce cytosolic messenger molecules (mechanism 3), which can go on to mediate gene expression (mechanism 4). Receptors can also mediate changes in cellular metabolism (mechanism 5). 

Ligand regulation. There are no clear cases for smooth muscle where a first or a second messenger molecule binding to a Ca channel of any type causes an activation (opening) of the channel or a shift of the voltage sensitivity. However, these remain as viable possible modes of regulation. 

Chemokines are small chemotactic cytokines that act as important messenger molecules between cells of the immune system. Chemokines produce their effects by activating a family of G-protein-coupled receptors. Chemokine receptors are all seven-transmembrane glycoproteins that are structurally related. They may be characterized into those that bind to specific ligands, or those that bind several chemokine ligands. There are also virally encoded (viral) chemokine receptors that represent shared receptors that have been transduced into the viral genome during evolutionary history (Premack and SchaU 1996). 

Bredt, DS and Synder, SH (1994) Nitric oxide a physiologic messenger molecule. Trends Biochem. Sci. 63 175-195. 

The neurotransmitters of the ANS and the circulating catecholamines bind to specific receptors on the cell membranes of effector tissue. Each receptor is coupled to a G protein also embedded within the plasma membrane. Receptor stimulation causes activation of the G protein and formation of an intracellular chemical, the second messenger. (The neurotransmitter molecule, which cannot enter the cell, is the first messenger.) The function of intracellular second messenger molecules is to elicit tissue-specific biochemical events within the cell that alter the cell s activity. In this way, a given neurotransmitter may stimulate the same type of receptor on two different types of tissue and cause two different responses due to the presence of different biochemical pathways within each tissue. 

Not released from glands chemicals acting more quickly than hormones, but like them consequentially. Sometimes all the above set of messenger molecules are described under the endocrine system. Some are released by the peripheral sense receptors. There are many other possible hormones such as glucose and several of the simplest hormones are related to bacterial sensors e.g. NO and some ions (see Chapter 6). 

The phospholipases (PLC) isozymes cleave the phosphodiester bond in phos-phatidyl-inositol-4,5-bisphosphate (PIP2) releasing two second messenger molecules inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) as shown before. The /1-isozyme are controlled by the Ga or G y subunits of the heterotrimeric G-proteins coupled to surface receptors. The y-isozymes are substrates for tyrosine kinases, such as growth factors. 

Snyder, S. H., A novel neuronal messenger molecule in brain the free radical, nitric oxide, Ann. Neurol. 32 (1992), p. 297-311... 

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