FIGURE 4.

Vesicular synergy. Shown in the left panel, a VMAT2⁺ SV undergoes (1) vesicular acidification, then (2) VMAT2 exchanges two H⁺s for DA to achieve (3) baseline vesicular DA concentration and subsequent (4) baseline DA release. Shown in the right panel, a VGLUT2⁺/VMAT2⁺ co-expressing SV, (1) VGLUT2 transports GLU and Cl^– into SV, which potentiates (2) vacuolar-type H⁺ATPase to hyperacidify the SV, thus (3) more DA is drawn in via VMAT2 in exchange for protons, resulting in (4) greater intravesicular DA concentration and subsequent release (5).