GEL-ENTRAPMENT OF PERFLUOROCARBONS - A F-19 NMR SPECTROSCOPIC METHOD FOR MONITORING OXYGEN CONCENTRATION IN CELL PERFUSION SYSTEMS

Oxygenation is a major determinant of the physiological state of cultured cells. F-19 NMR can be used to determine the oxygen concentration available to cells immobilized in a gel matrix by measuring the relaxation rate (1/T1) of perfluorocarbons (PFC) incorporated into the gel matrix. In calcium alginate gel beads without cells the relaxation rate (1/T1) of the trifluoromethyl group of perfluorotripropylamine (FTPA) varies linearly with oxygen concentration, with a slope of 1.26 +/ 0.15 x 10(-3) S-1 muM-1 and an intercept of 0.50 +/- 0.04 s-1. During perfusion with medium equilibrated with 95%/5% O2/CO2, changes in PFC T1s indicate that the average oxygen concentration was reduced from 894 +/- 102 muM in the absence of cells to 476 +/- 65 muM and 475 +/- 50 muM in the presence of 0.7 x 10(8) EMT6/Ro and RIF-1 murine tumor cells per milliliter of gel, respectively. The presence of 0.2 mul of FTPA/ml of gel had no effect on the energy status of the cells as indicated by P-31 NMR spectra. To calculate oxygen gradients within the beads from the average PFC T1 of the sample, a mathematical model was used assuming that oxygen is the limiting nutrient for cell metabolism and that the cellular oxygen consumption rate is independent of oxygen concentration. Data for EMT6/Ro cells were fit using experimentally determined perfusion parameters together with literature values for cell volume and oxygen consumption rate. The average PFC 1/T1s predicted using different literature values for volume and oxygen consumption-1.10 +/- 0.10 and 1.28 +/- 0.36 s-1-agreed well with the experimentally measured value-1.104 +/- 0.004 s-1. Thus, the model is a suitable tool for calculation of oxygen consumption rates from PFC T1s in well-oxygenated cell perfusion systems.