Before revision:  Our simulations indicate that a combination of this asymmetry and an internal voltage source arising from the motion of the C-terminal tails can allow a current to be pumped across the microtubule wall and propagate down the microtubule through the lumen.
After revision:  Our simulations indicate that a combination of this asymmetry and an internal voltage source arising from the motion of the C-terminal tails causes a net current to be pumped across the microtubule wall and propagate down the microtubule through the lumen.