Depolymerization of microtubules alters membrane potential and affects the motional freedom of membrane proteins

Abstract

Two independent lines of evidence were obtained indicating that microtubule depolymerization affects the functions and the physical state of membranes in intact Chinese hamster ovary cells. The first type of evidence was obtained by using the dye dihexyloxacarbocyanine iodide to measure membrane potential before and after treatment with several microtubule active agents. Microtubule depolymerization resulted in a decrease in cell fluorescence, whereas stabilization of microtubules with taxol resulted in an increase to direct effects of the drugs on the plasma membranes for the following reasons: (1) effects were time dependent and required entry into the cells as indicated by the lack of fluorescence change in a multidrug-resistant mutant that does not accumulate antimicrotubule drugs and (2) a colcemid-resistant tubulin mutant did not show these effects on cell fluorescence. Evidence for altered motional freedom of membrane proteins in the plasma membrane was obtained by using electron spin resonance analysis of maleimide spin probe labeled cells. This study showed that depolymerization of microtubles results in increased motional microtubules function in mammalian cells to regulate the physical state of membranes and modulate membrane potential generated across cell membranes.