Oxygen Diffusion in Biological and Artificial Membranes Determined by the Fluorochrome Pyrene

Quenching of pyrene fluorescence by oxygen was used to determine oxygen diffusion coeffÉcients in phospholipid dispersions and erythrocyte plasma membranes. The fluorescence intensity and lifetime of pyrene in both artificial and natural membranes decreases about 80 % in the presence of 1 atm O, , while the fluorescence excitation and emission spectra and the absorption spectrum are unaltered. Assuming the oxygen partition coefficient between membrane and aqueous phase to be 4.4, the diffusion coefficients for oxygen at 37°C are 1.51 X 10 -5 cm2/s in dimyristoyl lecithin vesicles, 9.32 X 10 -6 cm~/s in dipalmitoyl lecithin vesicles, and 7.27 X I0 -s em2/s in erythroeyte plasma membranes. The heats of activation for oxygen diffusion are low (< 3 kcal/degree-mol). A dramatic increase in the diffusion constant occurs at the phase transition of dimyristoyl and dipalmitoyl lecithin, which may result from an increase in either the oxygen diffusion coefficient, partition coefficient, or both. The significance of the change in oxygen diffusion below and above the phase transition for biological membranes is discussed. Knowledge of oxygen diffusion rates in tissue is essential in evaluation of the role of oxygen in control of metabolism. Oxygen diffusion coefficient in skeletal muscle was found to be 1.3 X 10 -5 cm2/s by Krogh (1929). This value closely resembles the oxygen diffusion coefficient in other tissues, and in blood plasma (Hartr idge and Roughton, 1927) and erythrocytes suspension (Forster et al., 1957; Klug et al., 1956; Thews, 1968). The similarity in the oxygen diffusion coefficient between tissue and protein solutions is generally taken to mean that the membrane imposes no barrier for oxygen (Boag, 1969; Wittenberg, 1970). In this paper we a t tempt critical analysis of this assumption. Quanti tat ive determination of the oxygen diffusion constant is afforded by use of the diffusion-limited reaction between the paramagnetic species oxygen and the singlet excited state of a fluorescent probe molecule located in the membrane. Pyrene is chosen as probe because its inTHE JOURNAL OF GENERAL PHYSIOLOGY • VOLUME 6 5 , x975 • p a g e s 663-676 663 on Jne 0, 2017 D ow nladed fom Published May 1, 1975