Abstract:
The invention relates to a method for analyzing the effect of a gaseous medium on a biological test system using an extracellular metabolization system. The method consists of the following steps: a biological test sample is cultivated on a permeable carrier, the gaseous medium is guided over the surface of the biological test system in order to form an exposition atmosphere over the biological test system, the extracellular metabolization system is added to a conservation medium and the permeable carrier is brought into contact with a conservation medium that comprises the extracellular metabolization system below the permeable carrier, in such a manner that the extracellular metabolization system only passes through the permeable carrier and that the biological test system is not submerged by the conservation medium containing the extracellular metabolization system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of and Applicant claims priority under 35 U.S.C. §§120 and 121 of U.S. application Ser. No. 12/452,154 filed on Dec. 17, 2009, which application is a national stage application under 35 U.S.C. §371 of PCT Application No. PCT/DE2008/001007 filed on Jun. 16, 2008, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2007 030 413.9 filed on Jun. 29, 2007, the disclosures of each of which are hereby incorporated by reference. A certified copy of priority German Patent Application No. 10 2007 030 413.9 is contained in parent U.S. application Ser. No. 12/452,154. The International Application under PCT article 21(2) was not published in English. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for analyzing the effect of a gaseous medium on a biological test system using an extracellular metabolization system, and to a device for carrying out the method. 
     2. Description of the Related Art 
     Known in the art is to expose cellular test systems in the form of eukaryote cultures, in particular cell lines, primary cells, biopsies, lavages, isolates, PCLS and the like, to ex-vivo airborne substances of a native or artificial type so as to analyze the biological effect of these substances. The eukaryote cultures are here exposed to an artificial or natural test atmosphere, also referred to as exposition atmosphere. 
     Since the intermediate metabolic products of the specified airborne substances are often the first to become biologically active, a biological effect of the test atmosphere in the cellular test system only becomes detectable after having been able to form the specified intermediate metabolic products during a metabolization of the specified airborne substances. 
     Cited below are examples of cellular test systems in which an intracellular metabolization capacity was ruled out or confirmed:
     (a) Isolates of primary cells with rather varyingly defined metabolizing capabilities/capacities that differ as a function of the respective isolation technique and isolation batch (e.g., hepatocytes of rat livers or from human biopsies; M. J. Gomez-Lechon et al., Hepatocytes—the choice to investigate drug metabolism and toxicity in man: Ir. vitro variability as a reflection of in vivo, Chemico-Biol. Int. (2006), dol: 10.1016/j.cbj.2006.19.013).   (b) Immortalized hepatocyte cell lines that can have a varying metabolizing capability/capacity depending on subpopulation (e.g., the human hepatoma cell line HepG2; Aden et al. 1979).   (c) Genetically altered cell systems (e.g., cell lines derived from V79 with defined expression of specific cytochrome P-450 forms; A. Townsend et al., Modeling the metabloc competency of gutathione S-transferases using genetically modified cell lines, Toxicology 181-182 (2002) 265-269; N. Krebsfaenger et al., V79 Chinese Hamster Cells Genetically for Polymorphic Cytochrome P450 2D6 and their Predictive Value for Humans, ALTEX 20, 3/03, 143-154).   (d) Cocultures of metabolically competent cells and non-metabolizing cells of the primary target tissue of the noxae (S. Bremer et al., Detection of the Embryotoxic Potential of Cyclophosamide by Using a Combined System of Metabolic Competent Cells and Embryonic Stem Cells, ATLA 30, 77-85, 2002).   (e) Tissue sections (D. S. Pushparajah et al., Evaluation of the precision-cut liver and lung slice systems for the study of induction of CYP1, epoxide hydrolase and glutathione S-transferase activities, Toxicology 231 (2007) 68-80).   

     The complexity of culture processes along with the availability and reproducibility of metabolization efficiency can be disadvantageous relative to these cellular test systems with intracellular metabolization systems. 
     The aforementioned cellular test systems with intracellular metabolization system also do not compulsorily satisfy the requirements imposed by various internationally test provisions, for example the “OECD Guideline for the Testing of Chemicals” No. 473, which mandate the presence of a sufficiently efficient metabolization system. 
     In order to satisfy these test requirements, it is known that use can be made of cellular test systems without intracellular metabolization or cellular test systems in which the efficiency of intracellular metabolization has not been verified, which are exposed in flat-bottomed culture flasks or round culture flasks, so-called roller bottles. The cellular test system is here coated with a mixture of conservation medium and an extracellular metabolization system, and the test atmosphere is continuously passed through the flask. In order to thoroughly mix the conservation medium, extracellular metabolization system and test atmosphere, the culture flasks are shaken, tilted or rotated. 
     The disadvantage to this method is that no direct and defined contact is possible between the test atmosphere and cellular test system. Therefore, the result is imbued with less sensitivity and specificity, as well as with the absence of an exact dosimetry. 
     SUMMARY OF THE INVENTION 
     Proceeding from this prior art, the object of the invention is to provide an alternative method with a high sensitivity and selectivity to analyze the effect of a gaseous medium on a biological test system using an extracellular metabolization system, as well as a device for carrying out this method. 
     This object is achieved by a method for analyzing the effect of a gaseous medium on a biological test system using an extracellular metabolization system according to one aspect of the invention, as well as by an exposition device according to another aspect of the invention. Further developments and advantageous embodiments of the invention are discussed below. 
     The method according to the invention for analyzing the effect of a gaseous medium on a biological test system using an extracellular metabolization system encompasses the following procedural steps:
         Cultivating a biological test system on a permeable carrier;   Guiding the gaseous medium over the surface of the biological test system to form an exposition atmosphere over the biological test system;   Adding the extracellular metabolization system to a conservation medium;   Positioning the conservation medium with extracellular metabolization system under the permeable carrier with contact to the permeable carrier, in such a way that the extracellular metabolization system only passes through the permeable carrier, while the biological test system is not flooded with extracellular metabolization system.       

     The method according to the invention makes it possible to analyze the effect of a gaseous medium on a biological test system with a high sensitivity and selectivity using an extracellular metabolization system. 
     The method according to the invention satisfies the following conditions that are recognized as essential to the invention, responsible for the high sensitivity and selectivity of the method, and to be observed simultaneously during exposition of the biological test system in the exposition atmosphere:
     a) A direct and unobstructed contact is established between the exposition atmosphere and biological test system;   b) Contact is established between the exposition atmosphere and the extracellular metabolization system;   c) The reaction products of the metabolization reactions of the exposition atmosphere with the extracellular metabolization system are made accessible to the biological test system.   d) The conservation medium is made accessible to the biological test system.   e) The vitality of the biological test system is assured.   

     Regardless of whether the biological test system exhibits intracellular metabolization capabilities or the whether intracellular metabolization capabilities are completely absent in the biological test, not pronounced enough, not sufficiently reproducible or too vaguely defined, the method according to the invention uses a defined, extracellular metabolization system to ensure the metabolization capability. 
     The important factor is that the boundary layer comprised of a permeable carrier with biological test system exposed thereupon quasi physically separates the compartments “exposition atmosphere” and “conservation medium with extracellular metabolization system” from each other, so that the conservation medium with extracellular metabolization system can only pass through the permeable carrier in the manner prescribed by the invention. 
     In terms of the invention, a conservation medium is here and below also referred to as a culture medium, also referred to as a nutrient medium, with or without additives or a saline solution. 
     The gaseous medium as defined in the invention can be present as a pure gas or gas mixture, i.e., all substances (atoms, molecules, etc.) contained therein exist in the gaseous phase, and/or it can also serve as a carrier for solids and/or liquids. In particular, aerosols, atomized liquids, small liquid droplets (e.g., plant protective agents as a spray, etc.), suspended particles, solid particles (e.g., wood dust, etc.), gaseous suspensions, atomized suspensions or emulsions can be incorporated in the carrier gas as substances to be carried. 
     The method according to the invention makes it possible to easily analyze the biological effect of gaseous media of all kinds in routine applications using biological test systems that might under certain conditions not have an independent metabolization capacity in a safe manner, i.e., while retaining vitality, ensuring a high sensitivity for the method due to intensive contact between the exposition atmosphere and both the biological test system and extracellular metabolization system, and in particular observing diverse international test provisions, for example the OECD 473 known by the expert. 
     In addition, the method according to the invention enables the use of individually fabricated compositions of diverse external metabolization systems known to the expert, for example with cytochromes of laboratory animals or humans that can be specifically tailored to various specific metabolic characteristics of a biological test system. 
     The invention preferably involves the use of a permeable carrier designed in such a way as to be suitable for accommodating the biological test system on the one hand, and enable a separation of the gaseous phase, meaning the exposition atmosphere, from the liquid phase, meaning the conservation medium with extracellular metabolization system, on the other. Therefore, the pore size and pore density of the permeable carrier can vary as a function of the type of biological test system and the type and viscosity of the conservation medium. 
     A microporous membrane is preferably used as the permeable carrier. A gel is preferably used as the permeable carrier. To accommodate the biological test system, a culture flask can also be provided, for example a commercially available, so-called cell culture insert, wherein the permeable carrier constitutes the floor membrane of the culture flask. 
     A further development of the invention is characterized by the following additional procedural step:
         Regulating the passage of the extracellular metabolization system added to the conservation medium through the permeable carrier by prescribing a specific pressure that acts on the conservation medium with extracellular metabolization system.       

     It is further provided that the pressure acting on the conservation medium with extracellular metabolism system is selected in such a way that the extracellular metabolization system passes through the permeable carrier, but the biological test system is not flooded by the conservation medium with extracellular metabolization system. 
     One advantageous embodiment of the invention is characterized by the following additional procedural step:
         Regulating the evaporation rate over the biological test system by prescribing a specific temperature in direct proximity to the biological test system and/or prescribing a specific flow rate of the gaseous medium steaming over the surface of the biological test system.       

     Controlling the temperature, preferably in direct proximity to the biological test system, makes it possible to regulate the evaporation rate of the conservation medium with extracellular metabolization system passing through the permeable membrane, so as to prevent the biological test system from drying out, and hence dying off. 
     The evaporation rate also depends on the moisture content of the gaseous medium. The flow rate of the gaseous medium over the biological test system must be correspondingly regulated or controlled. 
     The regulation and control of these two aforementioned parameters along with the pressure acting on the conservation medium with extracellular metabolization system establishes defined conditions for analyzing the effect of a gaseous medium on a biological test system using an extracellular metabolization system. 
     The invention also relates to an exposition device for carrying out the method. The exposition device comprises:
         At least one permeable carrier, on which a biological test system is cultured;   At least one feed system, which can route a gaseous medium over the surface of the biological test system to form an exposition atmosphere above the biological test system;   A delivery system that contains a conservation medium with extracellular metabolization system and is designed in such a way that the conservation medium with extracellular metabolization system is in direct contact with the lower side of the permeable carrier, wherein   The permeable carrier is designed and situated inside the exposition device in such a way that the latter physically separates the conservation medium with extracellular metabolization system from the exposition atmosphere, wherein   The conservation medium with extracellular metabolization system can only be forced through the permeable carrier in a defined manner by means of a prescribed pressure, specifically in such a way that the conservation medium with extracellular metabolization system passes through the permeable carrier, but the biological test system is not flooded by the conservation medium with extracellular metabolization system.       

     The feed system comprises all devices suitable for routing the gaseous medium over the surface of the biological test system to form an exposition atmosphere above the biological test system. Such a device is known from DE 100 14 057 A1, for example. The disclosure of this patent application is hereby completely incorporated into the present application by reference. 
     The feed system preferably also encompasses all devices that use their structural design to realize the feeding of the gaseous medium in a special way, for example with a hyperbolic interior profile for the targeted separation of aerosol droplets. 
     The feed system further preferably also encompasses devices for electrostatically separating particles or droplets and/or a charging device. Such devices are known from DE 195 26 533 A1, for example. The disclosure of this patent application is hereby also completely incorporated into the present application by reference. 
     In a further development of the invention, the delivery system is sealed off from the feed system and exposition atmosphere, and the conservation medium with extracellular metabolization system can only come into contact with the exposition atmosphere through the permeable carrier. 
     According to the invention, the prescribed pressure can be set hydrostatically, or via at least one pump or some other pressure-generating means. 
     In a further development of the invention, the delivery system is designed in such a way that the conservation medium with extracellular metabolization system contained therein remains in the delivery system for the duration of the analysis. 
     The permeable carrier is preferably designed in such a way as to enable the accommodation of the biological test system on the one hand, and a separation of the gaseous phase, meaning the exposition atmosphere, from the liquid phase, meaning the conservation medium with extracellular metabolization system, on the other. The latter depends in particular on the type of biological test system, as well as on the type and viscosity of the conservation medium with extracellular metabolization system. 
     In one advantageous embodiment of the invention, a discharge system is provided, with which the exposition atmosphere can be removed from the exposition device after residing therein for a predetermined period. 
     It is further provided that the feed and/or discharge system is designed in such a way that the gaseous medium can be relayed in controlled fashion through the exposition device by means of an underpressure system or an overpressure system. 
     The preferred means for continuously generating a corresponding pressure differential between the feed and/or discharge device is a pump, which is situated in the discharge system from the standpoint of flow. To advantageously adjust the flow rate of the medium, it is especially preferred that it be possible to control the pump in terms of its pumping capacity. 
     In a further development of the invention, a removal system is best provided with which the conservation medium with extracellular metabolization system can be removed from the exposition device after residing therein for a prescribed retention period. 
     The delivery and removal system is preferably designed in such a way that the conservation medium with extracellular metabolization system contained therein is routed through the delivery and removal system in a continuous or pulsating flow, wherein at least one pump is preferably provided for this purpose. 
     One advantageous embodiment of the invention provides at least one heating device, with which the temperature of the exposition device can be entirely or partially controlled. 
     Controlling the temperature, preferably in direct proximity to the biological test system, makes it possible to regulate the evaporation rate of the conservation medium with extracellular metabolization system passing through the permeable membrane, so as to prevent the biological test system from drying out, and hence dying off. 
     The evaporation rate also depends on the moisture content in the gaseous medium. The flow rate of the gaseous medium over the biological test system must be correspondingly regulated or controlled. 
     In another advantageous embodiment of the invention, the exposition device according to the invention correspondingly also encompasses a device for regulating and controlling the flow rate of the gaseous medium over the biological test system. 
     The regulation and control of these two aforementioned parameters along with the necessary pressure acting on the conservation medium with extracellular metabolization system establishes defined conditions for analyzing the effect of a gaseous medium on a biological test system using an extracellular metabolization system. 
     The used biological test system is preferably either a eukaryote culture, especially preferably cell lines, primary cell isolates, tissue sections, reconstructed tissue such as cocultures, or genetically altered cells, or a prokaryote culture. Such a biological test system is preferably used in the aforementioned method according to the invention. 
     A further development of the invention provides that the exposition device be combined with a cell-based sensor array. 
     The term “cell-based sensor array” is understood as encompassing all devices suitable for analyzing the used biological test systems while positioning them on the permeable carrier in the exposition device. 
     In particular, this can be realized in the form of an online measurement, or an analytical system able to read out a measured value within shorter or longer time intervals. 
     For example, cell-based sensor arrays can be realized for end points based on the use of a fluorescence or luminescence measurement. To this end, the biological test system is provided with a fluorophore, the properties of which are correlated with the cellular condition, and can hence image that latter via fluorescence analysis with respect to certain aspects, for example by dyeing the cells with H 2 DCFDA to detect intracellular radical formation. Suitable optics, for example fiber optic, and an external light source and detector along with a controller and measuring sensor can then be used for light stimulation—i.e., excitation—and emission measurement—i.e., emission—directly on the biological test system on the membrane. For example, a corresponding arrangement can be provided for analyzing luminescence phenomena, e.g., in conjunction with expression analyses, such as reporter gene assays. 
     Cell-based sensor arrays can also be realized via electrical or electrochemical measurements, for example, in particular in the form of an electrical resistance measurement, or TEER, trans-epithelial electrical resistance, or in the form of an impedance measurement. 
     Another configuration for cell-based sensor arrays can involve an arrangement suitable for analyzing substances issued by the cell, for example enzymes like lactate dehydrogenase or cytokines, quantitatively or qualitatively in the conservation medium. 
     In particular, these arrangements are suited for permitting an analysis during an exposition process. 
     The invention further relates to the use of the method or the exposition device for exposing at least one biological test system in cigarette smoke or the like or in exhaust gases, preferably in automobile exhaust gases or industrial exhaust gases. 
     The invention also relates to the use of the method or the exposition device for analyzing environmental atmospheres, workplace atmospheres or room atmospheres. 
     The invention additionally relates to the use of the method or the exposition device for analyzing the effect of a gaseous medium on a biological test system in the area of product safety, user protection, pharmaceutical development production monitoring or medical technology. 
     The invention further relates to the use of the method or the exposition device for analyzing the effect of a gaseous medium on a biological test system while observing regulatory guidelines, preferably OECD guidelines. 
     One preferred application of the method according to one aspect of the invention or the exposition device according to another aspect of the invention involves the approval-relevant testing of technically manufactured atmospheres, for example gas preparations or mixtures, the manufacture and marketing of which require official approval under laws governing chemicals, and the safety of which must be demonstrated under EU law in tests that do not involve the use of test animals if at all possible. 
     The invention further relates to using the method or the exposition device for analyzing the effect of a gaseous medium on a biological test system specifically for analyzing toxicological effects, genotoxic effects, immunomodulatory or immunotoxic effects or other biologically or toxicologically relevant cellular changes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment depicted in the drawing will be used below to explain the invention. Shown on: 
         FIG. 1  is a schematic partial view of an exposition device suitable for carrying out the method according to the invention, and on 
         FIG. 2  is a schematic setup for a possible analysis on the effect of n-butane on a biological test system using an extracellular metabolization system. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The exposition device  10  shown schematically in a partial view on  FIG. 1  can also be transported in field tests, and exhibits a substructure  12 , a central structure  14  arranged on the substructure, and a superstructure  16  arranged on the central structure  14 . 
     The substructure  12  is designed as a tub  18 , which preferably consists of a polycarbonate. Situated below the tub  18  is an electrical heater  20 , which makes it possible to control the temperature of the exposition device  10 . 
     Also provided are a supply tank (not shown here) for holding a conservation medium with metabolization system added according to the invention, and a hose pump (not shown here) for conveying the conservation medium with metabolization system from the supply tank into the tub  18 . 
     The tub  18  of the substructure  12  is tightly joined with a plate  22  of the central structure  14  with the formation of at least one cavity  24 , to which the conservation medium with metabolization system can be routed. The plate  22  preferably consists of a polycarbonate. 
     Let it be noted that the terms tub  18  and plate  22  must not be construed as meaning that the tub  18  always exhibits a floor with pulled up walls and the plate  22  is only flat in design. The tub  18  can essentially also be flat in design, and the plate  22  can exhibit pulled down walls. This is shown by example on  FIG. 1 . Various transitional stages between the tub  18  and plate  22  with various profiles are also possible. 
     The plate  22  further exhibits at least one receiving means, in the present case in the form of a hole  26 , for accommodating a permeable carrier  30  provided with a biological test system  28 , here in the form of a culture flask  32 . 
     The culture flask  32  shown on  FIG. 1  is shaped like a beaker with a circular cross section, wherein the diameter conically tapers from the beaker opening  34  to the beaker floor  36 . The beaker floor  36  consists of a porous plastic material, for example polyethylene terephthalate. The culture flask  32  represents a liquid-permeable carrying structure for the permeable carrier  30 , in particular a microporous membrane  30 , which can be made out of various plastic materials depending on the requirement of the cells to be cultivated, e.g., polyethylene terephthalate as well. The microporous membrane  30  here carries the biological test system  28 . 
     The beaker floor  36  of each culture flask  32  projects into the cavity  24  formed by the tub  18  and late  22 . The beaker opening  34  is located above the plate  22 . 
     It is important that the culture flask  32  accommodated in each hole  26  of the plate  22  be sealed on the outer beaker wall relative to the plate  22  by means of a sealant  38 , preferably by means of a silicone bead. This is essential to the invention, since only in this way can it be ensured that the conservation medium with metabolization system can only pass through the microporous membrane  30  and come into contact with the exposition atmosphere. This prevents the conservation medium with metabolization system from being pressed upward passing by the culture flask  32 , and then disadvantageously getting into the beaker opening  34  from above, and hence into the culture flask  32 , or flooding the plate  22 . 
     The conservation medium with metabolization system is preferably supplied via an inlet opening  40  in the floor of the tub  18 . The conservation medium with metabolization system then fills the cavity  24  between the tub  18  and plate  22 , and comes into contact with the microporous membrane  30  on its  30  lower side. In order to now be able to press the metabolization system in the conservation medium through the microporous membrane  30  to the biological test system  28  cultivated on the membrane  30 , pressure must be exerted on the conservation medium with metabolization system. This takes place hydrostatically in the simplest case. To this end, the conservation medium with metabolization system is pumped via the hose pump to a level  42  within the cavity  24  lying above the beaker floor  36 , meaning above the microporous membrane  30 . By preferably shifting the culture flask  32 , i.e., changing the level of the permeable carrier  30 , the pressure can also be changed. 
     The necessary level or necessary pressure required to press the metabolization system with conservation medium through the microporous membrane  30  according to the invention depends in particular on the type of microporous membrane  30 , meaning on the pore size and pore density, and on the used conservation medium with extracellular metabolization system. The necessary pressure is hence determined empirically. 
     The exposition device  10  preferably exhibits an outlet opening  44  in the floor of the tub  18  through which the spent conservation medium with extracellular metabolization system can be discharged from the exposition device  10 , in this case by the conservation medium with metabolization system exceeding the specified level  42 . 
     Situated on the plate  22  of the central structure  14  is a superstructure  16  that encompasses a cover  46  with pulled down walls. 
     Another heater  48  for controlling the temperature of the exposition device  10  can be provided on the cover  46 . 
     Provided within the cover  46  is at least one hole, which is positioned over a culture flask  32  accommodated in the plate  22 . 
     Situated in this hole  50  is a flow inlet pipe  52  for the gaseous medium, one end  54  of which projects directly into the culture flask  32 , wherein the end  54  is positioned just above the biological test system  28 . The other end  56  of the flow inlet pipe  52  is positioned outside the cover  46 . The flow inlet pipe  52  is outwardly sealed relative to the cover  46 . 
     Located between the plate  22  and cover  46  around each culture flask  18  is another seal, preferably in the form of a gasket  58 . 
     Situated within the gasket  58  in the cover  48  still in direct proximity to the aforementioned hole  50  is an outlet opening  60  for the gaseous medium. 
     The outlet opening  60  is preferably connected with a vacuum pump (not shown here) to aspirate a gaseous medium through the flow inlet pipe  52  on the surface of the biological test system  28  and subsequently through the outlet opening  60 . 
     The gaseous medium can stem from the outside atmosphere when using the exposition device  10  in a field test. This makes it possible to analyze the effects of various naturally occurring atmospheres on a biological test system  28 , for example. 
     Naturally, it is also possible to allow the gaseous medium to be analyzed through the flow inlet pipe  52  without a vacuum pump. To this end, the flow guiding pipe  55  is connected with a pressurized supply flask (not shown here). 
     It is only important that there be a pressure differential between the flow inlet pipe  52  and outlet opening  60 , so that the gaseous medium can continuously flow over the surface of the biological test system  28  and, according to the invention, over the metabolization system. 
     The hose pump is serviced via a controlling/regulating unit (not shown here), so as to supply the biological test system  28  in the culture flask  32  with the conservation medium on the one hand, and to enable the metabolization system added to the conservation medium to pass through the permeable carrier  30  according to the invention on the other, specifically in such a way that the conservation medium with metabolization system is pumped via the hose pump to a level  42  within the cavity  24  lying above the beaker floor  36 , meaning above the microporous membrane  30 . The pressure acting hydrostatically on the conservation medium with metabolization system presses the metabolization system through the permeable carrier  30  only to such an extent that the biological test system  28  is not flooded by the conservation medium with metabolization system. 
     Therefore, the hose pump is provided not just to pump conservation medium into the cavity  24  to provide the biological test system  28 , but rather also ensures that the conservation medium with metabolization system in the cavity  24  between the tub  18  and plate  22  is exposed to pressure in such a way that the metabolization system can be pressed by the present microporous membrane  30  without the conservation medium with metabolization system flooding the biological test system  28 . A submersion of the biological test system  28  is here entirely undesired according to the invention. 
     In order to reliably achieve a situation where the metabolization system comes in direct proximity or into contact with the biological test system  28 , but the latter is not flooded by the conservation medium with metabolization system, it may make sense to use a sensor (not shown here) for determining the flow of conservation medium with metabolization system through the microporous membrane  30 , which is connected with the controlling/regulating unit of the hose pump, and relays corresponding signals to the controlling/regulating unit for activating/deactivating the hose pump. 
     Temperature sensors (not shown here) can further be provided on or within the cavity  24  filled with conservation medium and metabolization system, specifically for controlling the temperature of the conservation medium with metabolization system by means of the aforementioned heaters  20 ,  48 . 
       FIG. 2  shows a schematic setup for a possible analysis of the effect of n-butane on a biological test system using an extracellular metabolization system. 
     Two exposition systems  62  and  64 , here marked exposition box  1  and exposition box  2 , were used for the analysis. 
     Each exposition device  62 ,  64  exhibits nine permeable carriers in the form of microporous membranes. Lung cells of the V-79 line are sued as the biological test system. These were cultivated biphasically, i.e., on the air-liquid interface, on the microporous membrane beforehand, and then introduced into the respective exposition device  62 ,  64 , as shown on  FIG. 1 . 
     Each exposition device  62 ,  64  is filled with a conservation medium, specifically with a culture medium, wherein only the culture medium of the exposition device  64  has received an extracellular metabolization system, specifically a 3% S9 mix. 
     An S9 mix is known to the expert, but is also described, for example, in “D. M. Maron and B. N. Ames, Revised Methods for the  Salmonella  Mutagenicity Test, Mutation Research, 113 (1983) 173-215”. 
     Both the conservation medium without extracellular metabolization system, meaning without S9 mix, and the conservation medium with extracellular metabolization system, meaning with S9 mix, are basally in contact with each microporous membrane according to the inventive setup, and are each separated by the latter from the exposition atmosphere, which apically reaches the microporous membrane. 
     The conservation medium without or with extracellular metabolization system is continuously and reproducibly temperature controlled, and acts on the microporous membranes from below with a prescribed pressure as a function of the existing/absent S9 component in the conservation medium. 
     The biological test systems situated on the microporous membranes in these exposition devices  62 ,  64  are transported from the cell culture laboratory to an exposition site remote from the laboratory. 
     The exposition devices  62 ,  64  are there connected with the feed  66  and discharge  68  systems of the test  70  and reference atmosphere  72 . 
     The test atmosphere n-butane  70  is diluted with pure air or a mixture of nitrogen and oxygen. The end concentration contains 20.5% oxygen. 
     Exposure to a pure air control takes place parallel and simultaneously, accompanied by an exposure of biological test systems with and without added S9 mix in the culture medium. 
     The constant supply of test and reference atmosphere  70 ,  72  to the biological test systems at a flow rate of 10 ml/min/cm 2  is ensured over the exposition period by regulating the flow rate in an underpressure system. The test or reference atmosphere  70 ,  72  is guided over the biological test system, meaning the cell layers. 
     The exposure time measures at least 3 hours. 
     The exposition devices  62 ,  63  are then separated from their feed  66  and discharge  68  systems and transported back into the cell culture laboratory. 
     The microporous membranes with their biological test systems are removed. 
     The preparation of the biological test systems, meaning the V79 cells, is followed by: an analysis of the toxicity by means of a neutral red assay; an examination of the lactate dehydrogenase release; an analysis of apoptosis by means of annexin-V-assay; an examination of oxidative stress via an analysis of the intracellular glutathione status; an examination of genotoxicity by means of micronucleus and COMET assay. 
     REFERENCE LIST 
     Part of the Specification 
     
         
           10  Exposition device 
           12  Substructure 
           13  Central structure 
           16  Superstructure 
           18  Tub 
           20  Heater 
           22  Plate 
           24  Cavity 
           26  Hole 
           28  Biological test medium 
           30  Permeable carrier 
           32  Culture flask 
           34  Beaker opening 
           36  Beaker floor 
           38  Sealant 
           40  Inlet opening 
           42  Level 
           44  Outlet opening 
           46  Cover 
           48  Heater 
           50  Hole 
           52  Flow inlet pipe 
           54  End 
           56  End 
           58  Gasket ring 
           60  Outlet opening 
           62  Exposition device 
           64  Exposition device 
           66  Feed system 
           68  Discharge system 
           70  Test atmosphere 
           72  Reference atmosphere