Effect of Oxygen on Glucose Consumption in Porcine TMJ Disc

Objective:  To determine the glucose consumption and lactate production rates of temporomandibular joint (TMJ) disc explants at various oxygen levels.  Our hypothesis is that the local nutrient environment has a significant impact on cellular metabolic activities due to energy requirements and nutrient availability.

Methods:  Tissue blocks were diced from 5 regions of porcine TMJ explants and bathed in media of varying glucose concentrations (0.5, 1, 5, 10, and 25 mM).  Oxygen tensions within an incubator were maintained at 3 levels during the course of experiments (2.5, 5, and 21% O₂).  Glucose and lactate concentrations were measured after 5 and 16 hours exposure time.  Consumption and production rates were calculated from the resulting concentration difference, cell densities, and time.

Results:  Glucose consumption rates (GCR) increased with increasing glucose concentrations demonstrating substrate dependence.  This same trend was not apparent for lactate production rates (LPR) at high oxygen tension.  Decreasing oxygen concentrations increased the glucose consumption and lactate production, indicating a positive Pasteur Effect. Average (n=5) GCR and LPR near estimated physiological conditions of 5% O₂ and 5mM glucose were 19.1±3.0 and 11.9±5.6 nmol/million cells/hour, respectively.

Conclusion:  GCR was substrate dependent suggesting that nutrient utilization was highly regulated and affected metabolic activities.  The positive Pasteur Effect shows that at low oxygen concentrations TMJ disc cells undergo a greater amount of glycolysis than oxidative phosphorylation for energy needs.  The transition point likely occurs between 2.5% and 5% O₂ (the 1:2 ratio of glucose consumption to lactate production associated with glycolysis disappears).  The low glucose consumption at high O₂ found in TMJ discs is significantly different from the trends observed in intervertebral discs and articular cartilage, and may be related to the higher mitochondria content found in TMJ disc cells.  (Supported by NIH T32DE017551 and F31DE020230.)