Steady Measurement of Glucose Metabolism of Hepatocyte

Production of hybrid artificial organs for implantation is one of the main topics of tissue engineering. A large organ consisting of soft tissues requires a high cell density, c.a. 10⁸ cells/mL, to satisfy the same physiological metabolic rate per organ-volume as an organ in vivo. Therefore, the supply of oxygen and nutrition to all the cells composing the soft tissue is always critical problem for the in vitro artificial organ production. Energy metabolic rates, such as oxygen and glucose metabolism rate, of single cell at various temperatures are the basic data for designing the oxygen and nutrition transport in an artificial organ. It is reported that several conditions including pH, temperature, oxygen or glucose concentration have effects on energy metabolism, although these interactions are not clearly quantitatively measured mainly because of the problems of measuring systems. In this study, convenient method to measure glucose consumption rate of hepatocyte (HepG2 cell line) at different temperature and glucose concentration is proposed. A device for the measurement was developed which consists of a small closed chamber with an inlet and an outlet of culture medium at the both ends of the chamber. On the one side of the walls in the chamber, confluent HepG2 on a coverslip was installed. Culture medium supplemented with various concentration of glucose was supplied to the open flow chamber in a constant flow rate. The whole chamber was in a thermostatic bath to keep the temperature in the chamber constant. Glucose consumption rate can be calculated by measuring the difference between glucose concentration of inlet culture medium and outlet culture medium, the flow rate and the number of cells in the chamber. Enzymatic analysis using D-Glucose-HK allows quantification of the sample glucose concentration. The advantages of the proposed method include; 1) small number of cells is required for the measurement, c. a. 10⁵cells, 2) the flow pattern and the glucose supply are in steady state. Especially the latter advantage made it possible to evaluate the effects of different conditions on the glucose consumption rate. Since the most of the metabolic rate were measured under unsteady state, conditions, such as pH, oxygen concentration and glucose concentration, were changed sometime drastically during the measurement. The results provided the several parameters of Michaelis-Menten kinetics at various temperatures.