Gaseous exchange

3) Is gaseous exchange with the atmosphere allowed or should the vessel be sealed off  

A variety of C02 incubators are now available which automatically control temperature and pC02. Some also have an automatic humidity control but usually they operate with a tray of water in the base in an attempt to maintain 98% relative humidity. The water in the tray must be changed regularly to prevent contamination. Humidity must be maintained high to prevent evaporation of water from the medium in open vessels. Such vessels can be obtained with baffles or rings in the lids to reduce air circulation. 

The problem with incubators is the rapid loss of controlled conditions when the door is opened. This is minimised if the circulation fan switches off on opening the door and most incubators have a C02 purge which rapidly restores the COz level. 

Some incubators also allow p02 to be controlled but the most imporant factor is temperature, especially for those working with temperature sensitive cells and viruses. Constant temperature throughout the incubator is maintained by fan assisted circulation. However, fans cause vibration and can be the cause of patterning in which the cell density varies in a regular way over the bottom of the culture vessel. Another cause of patterning is the holes in the shelf of the incubator. When a cool vessel containing a cell suspension is placed in a warm incubator the flask heats more quickly where it is in contact with the metal of the shelf and this sets up currents within the suspension leading to redistribution of the cells. 

C02 incubators are available from a number of companies, e.g. Bellco, Forma, Gallenkamp, Grant, Heracus, Leek, Damon/IEC, Napco and Queue (see Appendix 3). 

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Figure 8.15 Warburg manometer. Prior to any readings being taken, the manometer fluid in the inner limb is adjusted to the zero position by means of the pressure screw at the base of the manometer. Changes in the height (h) will then reflect the pressure changes in the flask which result from any gaseous exchange during the reaction.

The sequel to acute injury depends on the potency and concentration of the toxic agent and the duration of exposure. Potent gases produce a severe vascular reaction and alveolar flooding. The fluid prevents gaseous exchange, and death of the human or animal ensues. After acute mild nonlethal damage, excess fluid is removed and the resistant Type II cells proliferate and reline the alveoli. The cells subsequently differentiate into Type I cells. 

Even though subsequent development of visible injury may be as much a property of basic plant metabolism (44), it is necessary that stomata be open during exposure to the gas (42, 43) in order for leaves otherwise potentially ozone-sensitive to manifest injury symptoms. Thus, after the primary tissue barrier to gaseous exchange is traversed, the second barrier is the plasma membrane. Recent work has shown that ozonation can disrupt ion and water flux at the plasma membrane (45, 46), While membrane functional disturbance need not be indiscriminate (25, 46), the cited work supports the suggestion that cellular membranes represent a principal locus of ozone action (10, 39, 47, 48),... 

T.H. Shaffer, D. Rubenstein, D. Moskowitz, M. Delivoria-Papadopoulos, Gaseous exchange and acid-base balance in premature lambs during liquid ventilation since birth, Pediatr. Res. 10 (1976) 227-231. 

Figure 3.10 The structure of the mammalian respiratory system (A) trachea, (B) bronchiole, (C) alveolar sac with blood supply, (D) arrangement of blood vessels around alveoli, (E) arrangement of cells and airspaces in alveoli showing the large surface area available for absorption, (F) cellular structure of alveolus showing the close association between (G) the endothelial cell of the capillary (H) with erythrocytes and (I) the epithelial cell of the alveolar sac. The luminal side of the epithelial cell is bathed in fluid, which also facilitates absorption and gaseous exchange. Source From Ref. 1.

Farquhar GD, Firth PM, Wetselaar R, Weir B (1980) On the gaseous exchange of ammonia between leaves and the environment - determination of the ammonia compensation point. Plant Physiol 66 710-714... 

Concentration polarization may be a possible explanation for this erratic permeability coefficient behavior however, the influence of concentration polarization in gaseous exchange regimes such as the one herein reported is quite doubtful and subject to dispute(7 ). Alternative possibilities include (a) permeator functional loss due to on-going membrane compaction,... 

Culture flasks with vented filter caps allow for gaseous exchange between the culture and the incubator while protecting the cells from airborne microbial contamination. 

Fig. 2.24. Fugacity ratios (a) and gaseous exchange flux (b) between air and river water for PAHs and PCBs from Seoul Metropolitan city in 2001-2002 (quoted from Kim (2004)) fAV and fDW is fugacity in air vapor and dissolved water, respectively. Flux of PCBs was calculated on basis of observed vapor PCBs and NC indicate not calculated .

Here gaseous exchange, pH control and medium replenishment occur in a second vessel distinct from the cell growth chamber. From this vessel the medium is pumped into the growth chamber which may be a modified microscope slide, a roller bottle or a capillary bed etc. 

Two sorts of capillaries are used one for exchange of small molecules in solution and the other of silicone polycarbonate for gaseous exchange. The bundle of capillaries (about 150) is held in a tube into which a cell suspension (about 106 cells in 3 ml medium) is injected by an opening at the side (Fig. 3.5). When the cells have... 

Butler (1987) has considered the physics of gaseous exchange and rate of nutrient supply and concludes that a 100 1 culture running in the continuous mode may be more efficient than a 1000 1 batch system. Different systems for large scale production have been compared by van Wezel (1985)who concludes that continuous perfusion systems are the most efficient for production of cellular components. 

Gustafson, K.E., and Dickhut, R.M. (1997a) Gaseous exchange of polycyclic aromatic hydrocarbons across the air-water interface of southern Chesapeake Bay. Environ. Sci. Technol. 31, 1623-1629. 

The activities of many enzymes are affected by fluorides (5) or by ozone (03) and peroxyacetyl nitrate (PAN) (6). Cells and their constituents, such as mitochondria, chloroplasts, or cell membranes, are structurally or functionally abnormal after exposure to many pollutants (7, 8, 9). With leaves, the most commonly reported event is the appearance of lesions (10,11,12), but altered gaseous exchange (13) and levels of metabolites (14) have also been found. Many of the events associated with plants can be classified as a change in their size or shape or as an accumulation of a pollutant when it is fluoride (15) or a metal (16, 17). 

Suzuki, A.K., H.Tsubone, and K.Kubota. 1982. Changes in gaseous exchange in the lung of mice acutely exposed to nitrogen dioxide. Toxicol. Lett. 10(4) 327-355. 

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