Cellular messengers

Ion Channels. The excitable cell maintains an asymmetric distribution across both the plasma membrane, defining the extracellular and intracellular environments, as well as the intracellular membranes which define the cellular organelles. This maintained a symmetric distribution of ions serves two principal objectives. It contributes to the generation and maintenance of a potential gradient and the subsequent generation of electrical currents following appropriate stimulation. Moreover, it permits the ions themselves to serve as cellular messengers to link membrane excitation and cellular... 

Nitric oxide (NO) is a gaseous cellular messenger that transmits information between cells and within cells. In spite of its physiological role, NO is also a reactive species which is capable of reacting with biological molecules, and... 

Extra-cellular messengers Organic compounds synthesised using Cu and haem Fe... 

Finally, there are ion channels that respond to intracellular (as opposed to extracellular or environmental) chemical stimuli. These form part of cellular signaling pathways and may be opened by cellular messengers such as calcium ion, Ca +. Such channels are known as signal-gated ion channels. 

The biological effects of histamine (Table 15.1) are mediated via three receptor subtypes, HI, H2 and H3 that are linked to G protein but activate different cell-signalling systems. The histamine HI receptor is associated with the phospholipase C-catalysed formation of inositol 1,4,5-triphosphate (IP3) and 1,2-diacylglycerol (DAG). The H2-receptor is coupled to adenylyl cyclase, increasing the production of cAMP. The cellular messenger system involved in H3-receptor activation has not been fully defined, but it may couple to N-type Ca2+-channels. The genes encoding for HI and H2 receptors have been cloned. A mutation of the human H2 receptor has been linked to schizophrenia. 

Benzyl 2,2,2-trichloroacetimidate (bp 106-114 °C/0.07 kPa) alkylates alcohols in the presence of trifluoromethanesulfomc acid.311 Esters, imides, isopropylidene and benzylidene acetals are unaffected. This method allows the formation of benzyl ethers in molecules that are base-sensitive. In the example [Scheme 4,167],312 benzylation of the P-hydroxy ester 167.1.1 under the usual basic conditions would lead to retro-aldol reactions and/or elimination. A synthesis of the cellular messenger L-a-phosphatidyl-D-myo-inositol 3,4-bisphosphate exemplifies the use of trityl cation-promoted benzylation of two adjacent hydroxyls [Scheme 4.168].313314... 

Zhu J, Mix E, Olsson T, Link H (1994) Cellular messenger-Rna expression of interferon-gamma, 11-4 and transforming growth-factor-beta (Tgf-Beta) by rat mononuclear-cells stimulated with peripheral-nerve myelin antigens in experimental allergic neuritis. Clin Exp Immunol 98 306—312. 

A.U. Khan and T. Wilson, Reactive oxygen species as cellular messengers, Chem.Biol.l (1995) 437-445. 

Free radical biosensors may help to investigate the role of O2 and NO as cellular messengers by the direct, real-time measuring of free radical production directly as cell signal and in relation to stimuli to which the cell is exposed. Two types of biosensors have been developed. The first exploits the highly specific reaction of superoxide dismutase [69], while the other type is based on the cytochrome c reduction by O2 [53-55,143,147]. A further alternative uses protoporphyrin IX adsorbed to carbon material [263]. Here, however, peroxide is a strong interferent. 

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