Figure 11.

VSERT operates as a putative d-serine/H⁺ antiporter with a chloride leak or a coupled chloride cotransport. Although d-serine is a neutral amino acid, chloride acts as a counterion for V-ATPase and increases the pH gradient while reducing the membrane potential. Alternatively, chloride could modulate d-serine transport by regulatory binding to the transporter. SR is anchored to the membrane of GVs in which it converts l-serine into d-serine, allowing a local and efficient concentration of the gliotransmitter to be transported. However, preexisting d-serine is also taken up in GVs without any preference over a newly synthesized one.