Kinetics of distribution of 5-doxylstearic acid in mouse lymphocytes

The rate at which stearic acid nitroxide spin labels distribute through cells affects the interpretation of data obtained from these nitroxides. We used photoreduction of 5-doxylstearic acid (5DS) to determine the rate at which 5DS arrives at the outer half of the plasma membrane of mouse lymphocytes and macrophages. Our results show that 5DS is in equilibrium with the outer half of the plasma membrane of mouse lymphocytes over a time frame of 2 minutes or less. Thus, spectra data obtained from 5DS-labelled cells clearly reflects the spectrally averaged environment of all the cell membranes in lymphocytes and potentially other cells as well. This clarifies the observation that the spectral information obtained from doxylstearic acid nitroxides is relatively insensitive to environmental changes which would be expected to involve only the plasma membrane of the cell.