Physiology, question channeling

Since only less than 10% of G-6-P is channeled into the pentose phosphate cycle (under physiological conditions this percentage varies depending on the different tissues), the question must be discussed, what is the importance of this shunt. With regard to the resulting compounds Eqs. [(3), (5), (6), (7)] one mole NADPH2 appears twice. Furthermore, pentose phosphates are furnished for biosynthesis of nucleotides, nucleic acids, and fatty acids (D5, D6, DIO, H13, M5). 

This brief literature review provides compelling evidence in favour of a significant role for the sense of taste in fat preference in rodents. However, the presence of several putative lipid receptors (CD36, Kvl.5 channels, GPR120) in taste buds was not expected and raises questions about the physiological roles of these receptors. Furthermore, the taste-mediated perception of LCFA by CD36 would be unusual owing to the multifunctional nature of this protein. 

We conclude that a chain of hydrogen-bonded water molecules is able to translocate protons at a rate sufficient for measured ATP synthesis if the proton supply from the bulk phase is adequate. In the physiological pH range, the question of proton supply to a putative proton channel becomes... 

In the guinea pig TRPV1-positive nerve fibers are locahzed within the epithelium of the trachea and around smooth muscle and blood vessels and within the lower airways, in the vicinity of bronchi and bronchioles, and around alveolar tissue, whereas no TRPV 1 was found within airway epithelial cells (Watanabe et al. 2005). The physiological relevance of TRPVl mRNA expression, together with that of other ion channels in bronchial epithehal cells (Agopyan et al. 2003), remains questionable. Similarly, expression of TRPV 1 in dendritic cells (Basu and Srivastava, 2005) and the associated hypothesis that TRPV 1 orchestrates an early immune response has been challenged by failure to detect any functional TRPV 1 in these inflammatory cells (O Connell et al. 2005). We cannot exclude that in the airways, as in other tissues, TRPV 1 occurs in extraneuronal cells, from where it may contribute to homeostasis, inflammation, and ultimately the regulation of the tussive response. However, we underline that this hypothesis lacks conclusive experimental proof. 

The question arises now, that given these properties of sodium and potassium ions, how do ion channels recognise them, distinguish between them, and let the one or the other pass through them with high selectivity, as required for their proper physiological functioning. 

A key question is the extent to which any of these in vitro biochemical studies are useful for in predicting the respective GT activity and physiological functions in planta. Thus, in vivo factors which can influence GT activity in plant cells, such as cofactors, protein-protein interactions and metabolite channelling are absent in the in vitro assays. It is thus essential to examine the functional activity of GTs by altering their expression in planta, when probing the roles of these enzymes in development, metabolic or stress/defense-related pathways. 

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