Time-Dependent Fluorescence Depolarization of Fluorescein in Rat Thymus Lymphocytes

Abstract

Time behavior of fluorescence depolarization has been measured for fluorescein molecules introduced into rat thymus lymphocytes by means of a time-correlated single-photon-counting method under the excitation by a CW mode-locked Ar⁺ ion laser. The depolarization mechanism has been identified as restricted rotational Brownian motion of fluorescein in the case of very dilute dye concentration. The observed temperature dependence of rotatable angle of fluoresce in as well as that of rotational relaxation time is consistent with the expectation that the lymphocyte becomes softer as the temperature is raised. The relation between the quantities obtained by stationary and time-resolved experiments is discussed.