Figure 2.

Vesicular neurotransmitter transporters depend differentially on the two components of the electrochemical gradient of H⁺ (Δμ_H+). A V-ATPase generates a Δμ_H+ across the vesicle membranes. The vesicular transporters use this gradient to drive the transport of transmitters into secretory vesicles by coupling the translocation of transmitter to H⁺ running down Δμ_H+. The different vesicular transporters rely to different extents on the two components (Δ pH and Δψ) of this gradient. (A) VMATs and (B) VAChT transport their positively charged substrates coupled to the exchange of two H⁺, and hence rely primarily on Δ pH. (C) GABA and glycine are transported as neutral zwitterions by VGAT, which depends equally on both the chemical and the electrical component of Δμ_H+. (D) VGLUTs transport the negatively charged glutamate and thus rely more on Δψ than Δ pH. [Modified from Chaudhry et al. (2008b) with permission].