Current-voltage relation and reversal potential at junctional and extrajunctional ACh-receptors of the frog neuromuscular junction.

The relationship between synaptic current and membrane potential has been examined at junctional and extrajunctional end-plate receptors of the frog. At junctional receptors, the synaptic current-membrane potential relationship is linear for close range iontophoretic ACh application and non-linear when it is delivered from some distance. At extra-junctional receptors the current-voltage relationship is always non-linear. These non-linearities can be related to the fact that in both cases [ACh] on membrane outlasts the mean life-time of the synaptic channels. When their mean life-time is varied, the current-voltage relationship obtained at junctional receptors is no longer linear and the peak synaptic conductance increases or decreases with hyperpolarization as the channel life time is shortened or lengthened, respectively.