Topics on Signal Transduction

Calcium is a more ubiquitous second messenger than cAMP, regulating a diverse range of activities, including secretion, musele contraction, fertilization, gene transcription and cell proliferation (Pumey, 2005). Calcium is well suited for the role of an intracellular messenger for two main reasons  

Its immediate proximity provides the opportunity for it to enter the cytosol directly, through membrane channels, either from the extracellular environment or from the internal reticular compartment. 

Its distinctive coordination chemistry, i.e. the coordination numbers of Ca -complexes may vary between 6 and 12, and the arrangement around the coordination sphere is flexible. 

Ca + releases into the cytosohc compartment from the endoplasmic reticnlum (ER) occur through two families of structurally related ion channels, inositol triphosphate receptors (IP3RS) and ryanodine receptors (RyRs). IP3RS are virtually universal, whereas RyRs are most evident in excitable cells. 

TABLE 12.6 Examples of intracellular Ca -binding proteins of vertebrate origin 

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Nevertheless, we can already state with certainty that phytopolyphenols play a much wider role than acting merely as an antioxidant, which function was the first to be demonstrated for this extremely versatile class of plant secondary metabolites that appear to be important for human health. It is hoped that the extremely vigorous research activities involving the effects of phytopolyphenols on the signal transduction pathways in vivo will be initiated. We consider this topic one of the most exciting areas for future research in the field of traditional medicine and food science. 

Smooth muscle signal transduction has been the topic of several excellent review articles (Stull et al., 1991 Andrea and Walsh, 1992 Somlyo and Somlyo, 1994 Lee and Severson, 1994) and the reader is referred to these articles as well as other relevant chapters of this book for more details on current findings and controversies in the area of signal transduction in smooth muscle. To place the topic of enzyme trafficking within the broader context of smooth muscle contractile mechanisms, an outline of the currently described mechanisms of smooth muscle contraction is shown in Fig. 1. 

The two most important considerations in the design of new chemical sensors are the selectivity of the sensitive layer and the transduction mechanism by which the chemical interaction is transformed into a measureable physical signal. The present review is written from these two viewpoints. The literature on electroactive polymers (EP) is vast, growing, attractive for practical applications but sometimes also controversial. Application of these materials to chemical sensing is no exception. This topic is still relatively new, growing and, in some instances, too new to make any definitive statements. 

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