In vitro effects of colchicine on human erythrocyte membranes: an ESR study.

Colchicine (CC) is an antimitotic and antitubular agent which is currently used in medicine as a drug to treat various diseases. In spite of its widespread use the interaction of this drug with membranes is not yet known clearly. To characterize alterations in membrane molecular dynamics produced by CC, human erythrocytes were spin-labeled with 5-doxylstearic acid (5-DSA) and 16-doxylstearic acid (16-DSA), and membrane fluidity was quantified by measuring the changes in the order parameter (S) which reflects the anisotropy due to restricted motional averaging, correlation time (tau c) representing the spin label tumbling rate in the sample and phase transitions derived from ESR measurements. CC induced significant changes in both order parameter and correlation time at the surface of 5-DSA labeled membrane, but this was not the case at the core of 16-DSA labeled membrane. Order parameter, S and rotational correlation time, tau c, showed a biphasic character in the temperature range of 5-50 degrees C. This fact was used to calculate phase transition temperatures and activation energies of untreated (control) and treated erythrocyte cells with CC.