The effect of membrane potential on the half-time (t1/2) of the falling phase of the end-plate current was studied both in the absence and the presence of anticholinesterase. 2. In absence of anticholinesterase the relation between log t1/2 and membrane potential was linear at negative, and not linear at positive levels of membrane potential. This relation was not affected by the quantity of the released transmitter. 3. In presence of an irreversible anticholinesterase the relation between log t1/2 and membrane potential was shifted towards higher values of log t1/2. This shift could be counteracted by decreasing the quantity of the released transmitter. 4. It is concluded that in presence of anticholinesterase the decay of the end-plate current is slowed down because in this experimental condition the elimination of transmitter from the synaptic cleft is slowed down. 5. These observations were made in muscles bathed in Tris-HCl buffered Ringer solution. If a phosphate buffered Ringer solution was used, the relation between log t1/2 and membrane potential was linear throughout the range of membrane potentials studied. The reason why different buffers give different results is not clear and should be further studied.
