Buckling Microtubules in Vesicles

We study microtubules in vesicles using micropipet aspiration. A single microtubule in a vesicle buckles as aspiration increases the tension in the membrane, yielding a measure of the persistence length, 6.3 mm. A linear bundle of microtubules deforms the membrane into the shape of the Greek letter $\phi$. Under tension, this shape undergoes an abrupt and irreversible transition to a sphere and the microtubules are reorganized into a peripheral ring.