METHOD FOR MEASURING METABOLIC ACTIVITY OF ANIMAL OR PLANT TISSUES

Abstract: The metabolic activity of plant or animal tissue in a liquid medium is determined by measuring the electric current val­ ues or potential values generated by said plant or animal tissue namely by using an apparatus having electrodes 9 and 10 each having an anode 3, an internal electrode 8 and a liquid junction 4 for contact with an outside liquid.

Description: TITLE OF THE INVENTION METHOD FOR MEASURING METABOLIC ACTIVITY OF ANIMAL OR PLANT TISSUES Background of the Invention The present invention relates generally to a method for measuring the metabolic activity of animal or plant tissue and more specifically to a method for determining the number of active cells and metabolic activity or active parts of animal or plant tissue in a liquid containing such animal or plant tissue. In the culturing an animal tissue, the measurement of cell propagation has heretofore been carried out by counting the number of cells or the number of cell nuclei cultured by an overlapping culturing method directly by a haemocytometer; by means of an electric cell number counter; or by a method which quantitatively and biochemically determines and evaluates components such as protein, nucleic acid, etc. The electric cell number counter provides a simple and rapid method, as compared with other methods requiring complicated test procedures, but counts not only living cells but also dead cells and suspended particles. In culturing a plant tissue, particularly in a suspension culture of cells, the bond between cells is so strong that the culture liquor comprises a suspension of aggregated cells and single cells. Thus, the propagation of cells is usually evaluated as fresh cell or dry cell weight. These weights are, however, not direct reflections of the number of active cells, but include dead cells and solid materials, such a disrupted cell walls and the like. Culturing an animal and plant tissue is now being utilized for the production of food raw materials, medicaments and also for the production of physiologically active materials. It is a very important operation for the effective control of such production processes to measure the number of cells or metabolic activity originating from the animal or plant tissue in the culture liquor, and it is particularly desirable to make continuous measurements. However, as described above, the conventional methods for measuring the number of animal or plant cells or metabolic activity are complicated in operation, and have such disadvantages as failure to make continuous measurement, etc. and thus a novel, useful and simple method for measuring the metabolic activity of animal or plant tissue is in demand. To this end, it has previously been found that, when an electrode was suspended in a culture liquor of microorganisms, a current or a potential originating from the microorganisms corresponded quite well to the metabolic activity of the microorganisms; such finding being disclosed in Japanese Patent Application No. 101,897/78 (Published Unexamined Japanese Patent Application No. 29940/80) and commonly owned German Offenlegungsschrift No. 29 33 994. Summary of the Invention It has now been found by the present inventors that the metabolic activity of animal or plant tissue in a culture liquor can be determined by measuring a potential or a current originating from the animal or plant tissue through contact of an electrode. More specifically, it has now been found that a potential or a current measured by means of an electrode correlates well with the metabolic activity of the animal or plant tissue as determined by the heretofore known methods. Similarly, when the above-mentioned culture liquor is brought into contact with a potentiostatic system kept at a predetermined potential by two electrodes and a reference electrode (naturally the apparatus includes an apparatus producing a constant potential; this will be hereinafter applicable to any potentiostatic system) to measure the current originating from an animal or plant tissue, it was found that the measured current is in relation to metabolic activity. In the present invention, the liquid containing an animal or plant tissue means a suspension of an animal or plant tissue, a culture liquor of an animal or plant tissue, and animal blood corpuscles, lymphocytes, etc. The present invention thus provides a method for measuring metabolic activity of animal or plant tissue, characterized by contacting an electrode-or a potentiostatic system with a culture liquor, and measuring a current or a potential generated through reaction of the animal or plant tissue with the electrode or the potentiostatic system. A typical apparatus for carrying out the invention is an electrode having an anode and an internal electrolyte, a liquid junction for contact with an outside liquid, and an exposed cathode. Another apparatus is a potentiostatic system capable of maintaining an electrode comprising two electrodes and a reference electrode constant. In any apparatus, a pair of electrodes or z potentiostatic system are used in combination, and a cathode of one electrode or potentiostatic system is covered with an animal or plant tissue-impermeable membrane, to apply to actual measurement. It was found that the difference in measured current value (hI) or potential value (hE) between two electrodes or potentiostatic systems corresponds well to the metabolic activity of the animal or plant cells For the electrode of the present invention, such metals as platinum, gold, silver, and the like are appropriate. As the reference electrode, silver-silver chloride electrode, calomel electrode and the like are appropriate. Brief Description of the Drawings Particular embodiments of the present invention have been chosen for purposes of illustration and are shown in the accompanying drawings wherein: Fig. 1 is an elevation view, partially in cross-section, of one form of apparatus for carrying out the invention; Fig. 2 is an elevation view, partially in cross-section, of another form of apparatus for carrying out the invention; and Fig. 3 is a graph illustrating a particular relationship between metabolic activity of animal cells and current values obtained according to the invention. Detailed Description of the Invention With reference to Fig. 1, the present invention is carried out using an apparatus having electrodes 9 and 10 each having an anode 3, an internal electrode 8 and a liquid junction 4 for contact with an outside liquid. One electrode 10, in which an exposed platinum electrode 5 is covered with an animal or plant tissueimpermeable membrane 6, is an electrode for measuring the electrode-active materials other than the animal or plant tissue. The liquid junction 4 of electrodes 9 and 10 comprises a membrane having low electrical resistance, such as an ion exchange resin, ceramic, or the like. As the anode 3, metallic oxides, such as silver peroxide, silver chloride, silver dioxide, and the like or carbon or the like can be used. As the animal or plant cell-impermeable membrane 4 for covering the surface of the exposed platinum electrode 5, any animal or plant cell-impermeable membrane such as a cellulose membrane, a millipore membrane, etc. can be used, so long as it prevents the permeation of the animal or plant cells. Reference numerals 2 and 1 indicate respectively an ammeter or a potentiometer and a recorder of standard design to which electrodes 9 and 10 are connected in standard fashion. As illustrated, electrodes 9 and 10 are suspended in a housing 11 such as a culturing vessel equipped with, for example, a stirring bar 12 and magnetic stirrer 13, for carrying the measurements upon plant or animal tissue suspended in a liquid within housing 11. In Fig. 2 an alternate form of apparatus for measuring metabolic activity is illustrated and comprises a pair of potentiostatic systems (hereinafter referred to as "three-electrode method"). Each of the electrodes 14 and 15 of the individual potentiostatic systems has one reference electrode 16 for example, a calomel electrode and two electrodes 17 and 18. Housing 11 contains the culture liquor or tissue suspension into which the electrodes 14 and 15 are suspended. The exposed cathode 17 of one potentiostatic system 15 is covered with an animal or plant tissueimpermeable membrane 6, and is used for measuring electrodeactive materials other than the animal or plant tissue. As the animal or plant tissue-impermeable membrane those membranes as mentioned above in reference to Fig. 1 may be used. Each pair of potentiostatic systems is connected to a potentiostat 19 which, in turn, is connected to a recorder 1. As will be appreciated by those skilled in the art, the aforementioned two devices, can be simplified and modified, if required, and any apparatus structured as to have no adverse effect upon culturing animal or plant tissue cells and which can withstand the applied pressure, sterilization, etc. can be used. According to the present invention, the metabolic activity of an animal or plant tissue in a culture liquor or suspension is measured by means of an apparatus as generally described above. That is, an animal or plant tissue and electrode-active materials, such as coenzyme, formic acid, hydrogen peroxide, hydrogen etc., in a culture liquor or suspension generate a current or a potential through contact with cathode 5 of electrode 9 or cathode 17 of electrode 14 of the potentiostatic system. Onthe other hand, only the electrode-active materials contact with the cathode 5 of electrode 10 or cathode 17 of electrode 15 of the potentiostatic system to generate a current or a potential. The differences in currents or potentials measured as two electrodes 9 and 10 or electrodes 14 and 15 of two potentiostatic systems corresponds quite well to-the number of cells or metabolic activity of the animal or plant tissue. Thus, the difference in current or potential between electrode 9 and electrode 10 or the difference in current or potential between electrodes 14 and 15 of the two potentiostatic systems is correlated to metabolic activity of an animal or plant tissue. Therefore, the metabolic activity of the animal or plant tissue can be reliably measured from these values. While the principal and exact mechanism of the phenomena which the present invention utilizes is not fully understood, there is nevertheless a reliable correlation between the current or potential originating from animal or plant tissue and metabolic activity which permits determination of such metabolic activity. Certain specific embodiments of the present invention are illustrated in the following representative examples. Example 1 In this example, human origin cancer cells, i.e., KB cells, were inoculated into Eagle MEM medium (pH 7.2), placed in a square-type culturing bottle and subjected to stationary culture in a carbon dioxide incubator at 370C, and sampled every other day. The number of cells were counted with a haemocytometer. Simultaneously, an apparatus for measuring metabolic activity comprising two electrodes 9 and 10, shown in Fig. 1, with disk-type platinum electrodes (1 cm in diameter) as cathode, silver peroxide electrons 8 having a potential of 276 mV against saturated calomel electrode (5 mm in outer diameter and 14 cm in length) , as anode, anion exchange membrane (Selemion type keV, made by Asahi Glass K.K) as liquid junction 4, 1 M phosphate buffer solution (pH 7.0) as an internai electrolyte, and dialysis cellulose membrane as the covering membrane for the surface of cathode 10 of one of the electrodes 10 was suspended in the sampled liquid. The change in difference in current values (awl) obtained between the two electrodes with time is given in Table 1 below. Table 1 Culturing day 2 4 6 8 A Turner or cells (xl0/m1) 10.8 35.7 60.1 86.5 Current value Al (nA/cm2) 0.02 0.06 0.09 0.11 The results show a good correlation between the current value and the number of cells (living residue: 93.4%), Example 2 In this example, cancer cells L-1210 were inoculated into RPMI-1640 liquid medium (pH 7.2), placed in a square type culturing bottle and cultured at 37"C for one week in a carbon dioxide incubator. The cell-containing liquid was diluted with physiological saline water, and the number of cells were counted by means of an electric cell counter. At the same time, the current of the diluted, cell-containing liquid was measured according to the three-electrode method with a pair of potentiostatic systems comprising platinum electrodes 17, platinum electrodes 18 and silver chloride electrodes 16 (reference electrodes), shown in Fig. 2 (the cathode 17 of the electrode 15 of one potentiostatic systems was covered with a dialysis cellulose membrane), and the relation between the number of cells and the difference in current values (#1) obtained between the pair of potentiostatic systems is shown in Table 2 below. Table 2 3 A 5 6 Number of cells ( /ml) 10 10 10 10 Current value Al (nA) 213 116 31 10 The results in Table 2 are examples measured under an applied voltage of -500 mV, and a good correlation was established between the number of cells and the difference in current values (hI) obtained. Example 3 In this example, 0.2 ml of DDY-sWrain mouse blood was sampled, and admixed with 10 ml of physiologically saline water. The supernatant was admired with a drop of Saponin solution to perform hemolysis. The number of leukocytes was counted by means of an electric cell counter. On the other hand, the current of the leukocyte-containing solution was measured according to the three-electrode method, using the same apparatus as used in Example 2. The relationship between the number of leukocytes and the dif reference in current values (hI) are shown in Table 3 below. Table 3 Number of leukocytes ( /mm3) 600 3400 17500 84500 Current value hI (nA) - 160 190 280 712 The results in Table 3 were obtained unaer an applied voltage of -550 mV, and correlations were established between the number of leukocytes and the difference in current values (#I) obtained. Example 4 In this example, callus of Vinca rosea was inoculated into 100 ml of Murashige-Skoog liquid medium containing 0.5 ppm of kinetin and 0.1 ppm of 2,4-aichicro- phenxyacetic acid, placed in a 300 ml Prlenmeyer flask and cultured at 300C in a shaking cultivator at 100 rmp. The current value of the culture liquor was measured by means of the same apparatus with two electrodes as used in Example 1, and compared with the fresh cell weight (FCW) determined by standard procedure. The results are shown in Table 4 below. Table 4 Culturing dav 1 6 10 15 20 FCW (ma/ml) 10.2 50 176 321 334 Current value Al (nA) -9.5 -9.2 -6.7 -3.0 -3.1 A good correlation was observed between FCW and the difference in current values (Al) . Similarly, the results obtained according to the three-electrode method by means of the same apparatus as used in Example 2 are shown in Table 5 below. Table 5 Culturing day 1 6 10 15 20 FCW (mg/ml) 10.2 50 176 321 334 Current value Al (nA) 10 15 27 31 32 Table 5 shows the results obtained under an applied voltage of -200 mV, and a good correlation was observed between FCW and the difference in current values (hI) obtained, as in Table 4. Example 5 In this eample, Namalwa cells were incubated in a spinner containing RPMI-1640 medium (pH 7.2) comprising 20E fatal calf serum and 100 units of Penicillin and Streptomicin at 360C for 24 hours. The number of viable cells were counted with a haemocytometer chamber after straining with 0.2 Erythrocin. Fig. 3 shows the polarogram of various Namalwa cell suspensions which were diluted with normal saline (0.85% NaCl). As is apparent from Fig. 3, the output currents from a potent-ostnt in the range of more than + 400 mV depend on the number of viable cells.

Claims: WHAT IS CLAIMED IS: 1. A method for determining the metabolic activity of animal or plant tissue in a liquid medium which comprises measuring the difference between the current value or potential value of said animal or plant tissue and the current value or potential value of the liquid medium. 2. A method according to claim 1 wherein said measurement is carried out by suspending two electrodes in said liquid medium, one of said electrodes being covered with a membrane impermeable to said animal or plant tissue and comparing the current value or potential value of said two electrodes. 3. A method according to claim 1 wherein said measurement is carried out by suspending two potentiostatic systems comprising two exposed electrodes and a reference electrode in said liquid medium, one of said potentiostatic systems having one of its exposed electrodes being covered with a membrane impermeable to said animal or plant tissue and comparing the current or potential of said two potentiostatic systems.

Inventors: MOTOHASHI, RYOICHI, SAKATO, KUNIAKI, TANAKA, HISAO
Applicants: KYOWA HAKKO KOGYO CO., LTD
Application year: 1980
Main classification: C12M1
IPC codes: G01N27, C12M1