Secretory system evaluation

The suitability of the most prominent secretory systems among these organisms from the viewpoint of an integrative process design for the manufacture of recombinant proteins will be evaluated in the next section by discussing their potential productivity and their physiological properties. 

On the other hand, acidification of phosphate buffer, assuming absence of loss of alkaline or acid salt by a specific transport mechanism, can be shown to evaluate H ion secretion. Actually, since there is evidence that there may be greater permeability to the acid salt which includes a monovalent anion, while the alkaline salt includes phosphate in the form of a divalent anion, such rates may be underestimates of H ion secretion (1). In Fig. 4, a comparison between bicarbonate and phosphate acidification rate coefficients is made based on this view. This comparison must be made based on the respective rate coefficients, since acidification rates depend on the product of such coefficients with the driving force for acidification, that is, the difference between initial and final buffer base concentration in the tubular lumen. For a valid comparison, these driving forces have to be equal. It can be noted that both in control and in acetazolamide infused rats the sum of the phosphate and the dilution coefficient approximates that related to overall bicarbonate reabsorption. Thus, bicarbonate reabsorption could be broken down into two main components, one of them being H ion secretion, and the other related to processes like dilution and transport of bicarbonate out of the lumen, as evaluated by chloride inflow into non-buffer anion solutions like sulfate. According to this estimate, at least 55% of the bicarbonate reabsorbed under the described experimental conditions is transferred via the H ion secretory system, while the remainder may be attributed to the above described processes measured by means of estimation of... 

Very few published data exist on the evaluation of automated systems, though one report has been made of an automated absorption assay using Caco-2 cells cultured on both sides of polycarbonate membranes [93], The concept of culturing cells on the lower sides of the membranes was investigated as a means of improving the opportunity to study transport in the secretory basolateral to apical direction. However, this approach resulted in increased variability and impaired active transport properties of the cell monolayers, and was therefore not recommended. 

Cell lines, such as the Caco-2 and MDCK cells [27, 35, 47, 49, 57, 67, 128-133], have been used frequently to study different transporters in the GI tract. These cell lines have been evaluated for transport both in absorptive and secretory direction and in addition also been transfected with specified transporter systems of interests to yield new clones [23, 31, 72, 79, 80, 134] or co-cultures [135], Some of the uptake transporters belonging to the organic cation transporter (OCT) family have also been identified in cell lines such as the pig kidney cell line LLC-PK1, and MDCK [67, 136]. In fact, its presence in Caco-2 cells needs to be further elucidated as reports have shown both the absence and presence of transporters from this family of transporters [136-138],... 

INTESTINE Characterization of a membrane potassium ion conductance in intestinal secretory cells using whole cell patch-clamp and calcium-sensitive dye techniques, 192, 309 isolation of intestinal epithelial cells and evaluation of transport functions, 192, 324 isolation of enterocyte membranes, 192, 341 established intestinal cell lines as model systems for electrolyte transport studies, 192, 354 sodium chloride transport pathways in intestinal membrane vesicles, 192, 389 advantages and limitations of vesicles for the characterization and the kinetic analysis of transport systems, 192, 409 isolation and reconstitution of the sodium-de-pendent glucose transporter, 192, 438 calcium transport by intestinal epithelial cell basolateral membrane, 192, 448 electrical measurements in large intestine (including cecum, colon, rectum), 192, 459... 

In whole-body autoradiography studies in mice, the radiolabel originating from uC-labeled omeprazole was found to be confined to the gastric mucosa (Fig. 2.6). With a similar technique, and using both fight and electron microscopic evaluation, omeprazole was found to label only the tubulovesicles and secretory membranes of the parietal cell, which contain the H+, K+-ATPase [3]. Electrophoretic analyses of the proteins from such membranes, purified after systemic administration of... 

Evaluation of Secretory Expression Systems for Pharmaceutical Purposes 5... 

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