Signal transduction calcium signaling

Ikeda, S. R. 2001. Signal transduction. Calcium channels—link... 

Excitation of smooth muscle via alpha-1 receptors (eg, in the utems, vascular smooth muscle) is accompanied by an increase in intraceUular-free calcium, possibly by stimulation of phosphoUpase C which accelerates the breakdown of polyphosphoinositides to form the second messengers inositol triphosphate (IP3) and diacylglycerol (DAG). IP3 releases intracellular calcium, and DAG, by activation of protein kinase C, may also contribute to signal transduction. In addition, it is also thought that alpha-1 adrenergic receptors may be coupled to another second messenger, a pertussis toxin-sensitive G-protein that mediates the translocation of extracellular calcium. 

Grb-2 facilitates the transduction of an extracellular stimulus to an intracellular signaling pathway, (b) The adaptor protein PSD-95 associates through one of its three PDZ domains with the N-methyl-D-aspartic acid (NMDA) receptor. Another PDZ domain associates with a PDZ domain from neuronal nitric oxide synthase (nNOS). Through its interaction with PSD-95, nNOS is localized to the NMDA receptor. Stimulation by glutamate induces an influx of calcium, which activates nNOS, resulting in the production of nitric oxide. 

PTH has a dual effect on bone cells, depending on the temporal mode of administration given intermittently, PTH stimulates osteoblast activity and leads to substantial increases in bone density. In contrast, when given (or secreted) continuously, PTH stimulates osteoclast-mediated bone resorption and suppresses osteoblast activity. Further to its direct effects on bone cells, PTH also enhances renal calcium re-absorption and phosphate clearance, as well as renal synthesis of 1,25-dihydroxy vitamin D. Both PTH and 1,25-dihydroxyvitamin D act synergistically on bone to increase serum calcium levels and are closely involved in the regulation of the calcium/phosphate balance. The anabolic effects of PTH on osteoblasts are probably both direct and indirect via growth factors such as IGF-1 and TGF 3. The multiple signal transduction... 

Small ubiquitous calcium-binding protein. Calmodulin binds and regulates the activity of many protein targets involved in cellular signal transduction pathways mediated by calcium. Calmodulin is ranked among the most conserved proteins and plays a key role in many cellular processes. 

The smooth muscle cell does not respond in an all-or-none manner, but instead its contractile state is a variable compromise between diverse regulatory influences. While a vertebrate skeletal muscle fiber is at complete rest unless activated by a motor nerve, regulation of the contractile activity of a smooth muscle cell is more complex. First, the smooth muscle cell typically receives input from many different kinds of nerve fibers. The various cell membrane receptors in turn activate different intracellular signal-transduction pathways which may affect (a) membrane channels, and hence, electrical activity (b) calcium storage or release or (c) the proteins of the contractile machinery. While each have their own biochemically specific ways, the actual mechanisms are for the most part known only in outline. 

Use of biochemical and biological information for bioprocesses is also significant to the advancement of BRE. Here, the information on the signal transduction from external Ca was utilized for regulation of ginsenoside biosynthetic pathway of cultured cells of P. notoginseng. A quantitative study on the effects of external calcium and calcium sensors was conducted to... 

Fig. 3. A proposed signal transduction pathway regarding the external Ca effect on ginsenoside Rb synthesis by P. notoginseng cells. Ca signal changes are triggered by external Ca concentrations. The calcium signatures are decoded by calcium sensors, CaM and CDPK. UGRdGT is possibly modulated by the sensors in a direct or indirect (dashed lines) way. Changes of CDPK activity may result from increased synthesis or posttranslational modification of the enzyme (shown as CDPK ).

This linear scheme of signal transduction (Fig. 12) from hypothetical membrane receptors to [Ca " ] and IP3 increases, calcium-calmodulin interaction, kinases activation and gene transcription is clearly an oversimplification of the reality several receptors must exist that are connected to different transduction cascades that activate a series of defense genes. Cross-talking between the pathways further complicates the picture. However, this represents a starting model on which to elaborate more refined hypotheses. 

PBAN binding to a receptor results in signal transduction events to stimulate the pheromone biosynthetic pathway (Fig. 5). Receptor activation results in the influx of extracellular calcium and has been demonstrated in a number of moths [163-168]. The increase in cytosolic calcium can directly stimulate pheromone biosynthesis in some moths [165-168] or it will stimulate the production of cAMP [169,170]. So far cAMP has only been implicated in signal... 

Fig. 5 Proposed signal transduction mechanisms that stimulate the pheromone biosynthetic pathway in Helicoverpa zea and Bombyx mori. It is proposed that PBAN binds to a G protein-coupled receptor present in the cell membrane that upon PBAN binding will induce a receptor-activated calcium channel to open causing an influx of extracellular calcium. This calcium binds to calmodulin and in the case of B. mori will directly stimulate a phosphatase that will dephosphorylate and activate a reductase in the biosynthetic pathway. In H. zea the calcium-calmodulin will activate adenylate cyclase to produce cAMP that will then act through kinases and/or phosphatases to stimulate acetyl-CoA carboxylase in the biosynthetic pathway...

Ionized calcium (Ca2+) is the most common signal transduction element in cells [66], Excitable cells, like neurons, contain voltage-dependent Ca2+ channels, which enable these cells to drastically increase cytosolic calcium levels. Rapid fluctuations in presynaptic... 

In many cells, phosphoinositide signaling leads to an elevation in intracellular calcium levels through the release of calcium from intracellular stores in response to IP3-dependent gating of channels in the endoplasmic epithelium (Ch. 20). It is not known if IP3 plays a critical role in TRC transduction, but such a role would be consistent with recent findings that a Ca2+-activated cation channel, TRPM5, is essential for normal sweet, bitter and umami taste function [49,66-69],... 

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