Effects of Aminopyridines on Ionic Currents and Ionic Channel Noise in Unmyelinated Axons

ABSTRACT 4-amino-pyridine and most of its derivatives block the potassium conductance in the micromolar range of concentration. This blockage is strongly voltage dependent. The time and voltage dependency of the binding of 4-AP has been studied in internally perfused giant axons of the squid. The results suggest that 4-AP molecules can be displaced from their binding site under the effect of the electric field and a simple model which accounts for most data has been proposed. Interaction of 4-AP with the opening and closing of individual potassium channels has been tentatively analysed using spectrum analysis of membrane current fluctuations (noise) of small patches of the axonal membrane of the cockroach. The results suggest that 4-AP molecules block open or closed channels in an all-or-none manner.