The effect of temperature on the respiration of cultured neural cells as studied by a novel electron paramagnetic resonance technique

A new technique to study cellular respiration under steady-state conditions id described. For detection of oxygen concentration the technique utilizes lithium phthalocyanine crystals whose, electron paramagnetic resonance (EPR) spectra are highly sensitive to oxygen. A gas permeable poly(tetrafluoroethylene) (TFE) capillary (i.d. = 0.81 mm; o.d. = 0.86 mm) is used to control the oxygen flux to the sample of cultured neural cells (N1E-115) of 50 μl volume. The measured oxygen permeability of the TFE capillary exhibits Arrhenius law behavior (E_p = 21.2 kJ/mole) in the temperature range 15-43°C. The observed increase in the respiratory rate of the N1E-115 cells with temperature can be described with an apparent activation energy of E_a = 110 ± 20 kJ/mol. Cellular depolarization with 35 mM KCl increases the respiratory rate of the cells but gives the same activation energy. The results confirm a hypothesis that respiratory depolarizers affect only the total enzyme concentration and do not change the apparent E_a of the substrate-enzyme decomposition reaction. The theoretical treatment of oxygen diffusion in the system provides guidelines for designing steady-state cellular respiration experiments.