The effects of reagents affecting microtubules and microfilaments on the excitation of the squid giant axon measured by the voltage-clamp method

Electrophysiological responses of squid giant axons were monitored by the voltageclamp method when reagents reacting with tubulin (colchicine and vinblastine) or actin (cytochalasins B and D, and phalloidin) were internally perfused. Upon applying these reagents, the peak sodium current was reduced in amplitude and the steady-state current was shifted along the potential axis in the direction of depolarization. At the same time, both sodium and potassium conductances were reduced, and the time courses of sodium and potassium currents were affected. These experimental results further support our idea that the functional unit of the axonal membrane is not a single channel protein but is composed of proteins coupled with axoplasmic structures consisting mainly of microtubules and microfilaments underneath the axolemma, and that the nerve excitation implies a. manifestation of collectivity in the functioning of the channel proteins regulated by the axoplasmic structures (7).