Effects of taxol and colchicine on platelet membrane properties

The effects of the assembly-disassembly of microtubule on the membrane lipid fluidity, the fragmental motion of sulfhydryl groups of membrane proteins, and the functions of shape change and hypotonic shock response (shrinkage ratio) in human platelets were studied. We have employed electron spin resonance (ESR) utilizing spin labels for bilayer lipids or membrane proteins and microtubule reactive reagents to change microtubule assembly. Both, taxol, a microtubule stabilizing agent, and colchicine, a microtubule disrupting agent, did not affect the platelet membrane lipid fluidity detected by 5- or 16-doxylstearate. On the other hand, the mobility of sulfhydryl groups detected by 4-maleimide-tempo increased by taxol treatment and decreased by colchicine. Moreover, the temperature sensitivity of platelets below 20 degrees C decreased by taxol treatment, but unchanged by colchicine treatment. This behavior was similar to the shape change ability or the shrinkage ratio of platelets pre-treated with taxol, in which microtubule disassembly was inhibited due to taxol binding to microtubule. Therefore, it is confirmed that the assembly-disassembly state of microtubule which may control the ability of platelets to change shape, influences the mobility of sulfhydryl groups in platelet membrane proteins and its temperature sensitivity.