Cellular transport processes

Understanding and mimicking of the cellular transport processes are both challenging and rewarding from scientific and technological point of view. For example in certain inherited diseases (such as cystinuria), specific transport systems are either defective or missing [1]. Cystinuria is a human disease characterized by the absence of a transport system that carries cystine and other amino acids into kidney cells. Kidney cells normally reabsorb these amino acids from the urine and return them to the blood, but a person inflicted with cystinuria develops painful stones from amino acids that accumulate and crystallize in the kidneys. Similarly, there are many technological applications of these transport processes, e.g., bioseparations, bioextractions, and synthetic nano-bioreactors. 

Acute studies require cautious interpretation as chronic exposure of LLC-PKl cells to LFAB (1-2 days), which is more representative of events that occur clinically, resulted in profound toxic effects at concentrations similar to those of AmB (LFAB/AmB =1 1), manifested by changes in cellular transport processes and in morphology [151]. This finding raises questions as to the applicability and relevance of results derived from short-term in-vitro experiments to whole animal or clinical situations. 

Whistler, R L, Lake, W C, Inhibition of cellular transport processes by 5-thio-D-glucopyranose,... 

Can the phenomenon of H" "-flux mediated electro-osmosis provide the biodynamic principle which we have been looking for It is clear that cellular transport processes such as axonal transport and cytoplasmic streaming could directly result from proto-osmosis if the ATPases inject protons into the filamentous systems. Ciliary movements could possibly result from a periodic proto-osmotic insurge of fluid in the cilia. A relative (contractile) movement of two sets of filaments could be caused by a proto-osmotic loop flow between the pairs of the filaments by means of the associated visous drag couple. But the question of the relevance of the effect can be solved only if it can be shown that the magnitude of the effect is sufficient, quantitatively, to explain at least one biodynamic phenomenon. The best-studied system in this context, from structural and biochemical aspects, is that of muscles. The necessary quantitative data for the comparision of theoretical result with experiments is available, but it has to be first confirmed that the conditions for the proposed electro-osmotic flow obtain in muscles. 

The binding event could result in the translocation of the metal or some metal complex into the cell interior where interaction with intracellular membranes, enzymes, or transporters (Anner and Moosmayer 1992 Imesch et al. 1992 Stockand et al. 1993) could ensue (Brunder et al. 1988 Chang and Dawson 1988 Skroch et al. 1993). In view of these possibilities, it will clearly be difficult to distinguish primary and secondary effects of metals on cellular transport processes. 

The ABC-transporter superfamily represents a large group of transmembrane proteins. Members of this family are mainly involved in ATP-dependent transport processes across cellular membranes. These proteins are of special interest from a pharmacological point of... 

Deprived of their substrate in severe or prolonged hypoxia, some ATPase-driven systems, including ion pumps, may become impaired. Further, with the decrease in the availability of O2 as its terminal electron acceptor, the mitochondrial transport chain becomes increasingly unable to accept reducing equivalents from cellular metabolic processes. Hence the intracellular pH falls, subjecting the cell as a whole to a reductive stress and favouring those enzyme systems with acid pH optima. 

JR Williamson, SK Joseph, KE Coll, AP Thomas, A Verhoeven, M Prentki. (1986). Hormone-induced inositol lipid breakdown and calcium-mediated cellular responses in liver. In G Poste, ST Crooke, eds. New Insights into Cell and Membrane Transport Processes. New York Plenum Press, pp 217-247. 

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. 

In situ models are to evaluate absorption or membrane permeability under the physiologically relevant tissue condition. While the luminal environment can be modulated by the administered solution, the tissue condition is physiologically controlled. The estimated membrane permeability can be, in most cases, assumed to represent the transport across the epithelial cell layer at steady state or quasisteady state. However, one needs to be aware that the involvement of metabolic degradation, which may occur at the cellular surface or within the cytosol, can be a factor leading to biased estimates of membrane permeability and erroneous interpretation of the transport process. Particularly,... 

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