Electric fields of synaptic currents could influence diffusion of charged neurotransmitter molecules.

Rapid activation of synaptic receptor-channels evokes an ion current that flows through the narrow synaptic cleft; this exerts a significant voltage drop and therefore strong electric field (10(4) V/m range) directed towards the current sinks in the cleft. To what extent this field affects fast diffusion of charged neurotransmitter molecules is not known. We draw a theoretical framework for this complex electrodiffusion phenomenon and establish the basic relationships between the synaptic current and the time course of neurotransmitter in the cleft. The analyses predict that excitatory currents could significantly accelerate the dispersion of negatively charged molecules from the cleft while attracting the positively charged molecules towards the current sinks. This previously unrecognized mechanism should affect the kinetics of synaptic receptor currents, thus contributing to fast synaptic signaling in the brain.