[16] Ion-coupled neurotransmitter transport: Thermodynamic vs. kinetic determinations of stoichiometry

This chapter describes ion-coupled neurotransmitter transport, where ions and net charge move across the membrane coupled to neurotransmitter flux, then ion gradients and membrane potential influences the steady-state distribution of neurotransmitter.

Abstract

Publisher Summary This chapter describes ion-coupled neurotransmitter transport. Neurotransmitter transporters are molecular machines and, like other machines, they require an input of energy in order to perform useful work. The work of these machines is to move a neurotransmitter across a lipid bilayer from a low concentration in the extracellular medium to a higher concentration in the cytoplasm. The energy source that powers this work is the unequal distribution of Na + , K + , and Cl − and the electrical potential across the membrane. All plasma membrane neurotransmitter transporters couple the symport of their cognate neurotransmitter substrate with Na + ions but the number of Na + ions moving with each neurotransmitter molecule varies from one to three depending on the transporter. Depending on the number of ions moving, their direction of movement, and the charge on the substrate neurotransmitter, there is net movement of charge across the membrane with each neurotransmitter molecule transported. If ions and net charge move across the membrane coupled to neurotransmitter flux, then ion gradients and membrane potential influences the steady-state distribution of neurotransmitter. The ultimate concentration of extracellular neurotransmitter is determined by these driving forces and how they are coupled to transport.