Transport processes regulation

Transport processes regulating gaseous flux from soil to the water column and into the atmosphere... 

There is growing evidence implicating Na+-dependent solute transporters and intracellular as well as extracellular Ca2+ in the physiological regulation of the paracellular pathway [81,203,204], Such modulation of paracellular permeability is especially important for drugs such as peptides and oligonucleotides that exhibit poor permeability characteristics across both the cornea and the conjunctiva [150,152,154,155], In addition, ion transporters such as Cl and Ca2+ channels have been implicated in macromolecular transport (see Sections IV.B.2 and IV.B.4). In the following discussion, some key ion transport processes and their possible roles in solute transport across epithelial tissues are summarized. 

It has been known for some time that the enteric nervous system does not simply regulate smooth muscle contraction, but is intimately involved in the control of transport processes in enterocytes. Nerve fibres in the mucosa terminate subjacent to the basement membrane of epithelial and entero-endocrine cells, on which muscarinic acetylcholine receptors (mAChRs)... 

Metal ions play an important role as catalysts in many autoxidation reactions and have been considered instrumental in regulating natural as well as industrial processes. In these reactive systems, in particular when the reactions occur under environmental or in vivo biochemical conditions, the metal ions are involved in complicated interactions with the substrate(s) and dioxygen, and the properties of the actual matrix as well as the transport processes also have a pronounced impact on the overall reactions. In most cases, handling and analyzing such a complexity is beyond the capacity of currently available experimental, computational and theoretical methods, and researchers in this field are obliged to use simplified sub-systems to mimic the complex phenomena. When the simplified conditions are properly chosen, these studies provide surprisingly accurate predictions for the real systems. In this paper we review the results obtained in kinetic and mechanistic studies on the model systems, but we do not discuss their broad biological or environmental implications. 

Flik, G., Verbost, P. M. and Wendelaar Bonga, S. E. (1995). Calcium transport processes in fish. In Cellular and Molecular Approaches to Fish Ionic Regulation. eds. Wood, C. M. and Shuttleworth, T. J., Fish Physiology Series, Vol. 14, Academic Press, San Diego, pp. 317-342. 

The metabolites are transformed and translocated by reactions and transport processes, both modified by allosteric regulation. 

Taiz and Zeiger (2002) give a full account of this topic. Mineral ions absorbed from solution outside the root surface must be transported across the root to the main long-distance transport vessels in the xylem, through which they reach the shoot. This process is highly specific for different ions and molecules and is closely regulated. The regulation is in part a fnnction of the anatomy of the varions root tissues and in part a fnnction of active transport processes in root cells. The pathways and transport processes are affected by root adaptations to anoxia. 

The transport from nucleus to cytoplasm is accompanied by modification at the 5 - and 3 -end of the pre-RNA, as well as by processing (splicing) of the primary transcript. The 3 -end modifications and sphcing decide which information contained in the primary transcript is made available for protein biosynthesis. The information content of the processed mRNA can be specifically influenced by these processes. This has an important impact on the tissue- and cell-specific protein expression. 3 -modification and splicing are tightly coupled to extranuclear transport. Interventions in the transport process are another possibihty for a regulation at the post-transcriptional level. 

Further examples of substrates of protein kinase C are the epidermal growth factor receptor (see Chapter 8), a Na7H exchanger protein, and Raf kinase (Chapter 9). Activation of protein kinase C may, as the examples show, act on other central signal transduction pathways of the cell it may have a regulating activity on transcription processes and it is involved in the regulation of transport processes. Many substrates of protein kinase C are membrane proteins and it is evident that membrane association of protein kinase C is of great importance for the phosphorylation of these proteins. 

As regulation systems involving effectors, coupled transfers of charges and of mass, gates and pumps, transport processes extend towards the chemistry of information storage and retrieval at the molecular level, and are a major component in the design of molecular ionic devices (see Section 8.4). They thus open wide perspectives for the basic and applied developments of the functional features of supra-molecular chemistry. 

Calcium ions are essential in a variety of physiological processes including blood clotting, release of neurotransmitter at the synapse, cell division, cell adhesion, secretion, bioluminescence, membrane permeability, muscle contraction, and bio-mineralization35,174 176. In most of these systems, the disposition and functions of membrane proteins are a key in transport and regulation of calcium. Thus in order to understand the functionality of calcium one should look at a membrane system where the biochemical interplay of calcium is known in detail. 

Blood transports chemicals from the respiratory surface throughout the tissues of the organism. Several authors have attempted to elucidate the relative importance of this and other transport processes in regulating the uptake of chemicals via the gills in fish (e.g., Barber et al., 1988 and 1991 Erickson and McKim, 1990b Gobas and Mackay, 1987). In most cases, it has been concluded that the role of blood flow in regulating the overall rate of... 

---