Fig. 5.

Inhibition of VMAT1 and VMAT2 activity by Gαo₂ or GMppNp in permeabilized BON cells.A, [³H]Serotonin uptake performed in the presence of 2 mm histamine (VMAT1 condition) was inhibited by 10 nmAlF₄⁻-activated Gαo₂ (*,p < 0.004). [³H] histamine uptake (200 nm final concentration of histamine) was inhibited by 10 nm AlF^4₋-activated Gαo₂, whereas heat-denaturated protein had no effect or (*p < 0.02, calculated by Students't test). Values (n = 3 ± SD) represent the reserpine-sensitive uptake. Monoamine uptake in the presence of reserpine was 0.42 ± 0.035 and 0.33 ± 0.001 pmol/mg of protein for VMAT1 and VMAT2 activity, respectively.B, Increasing concentrations of AlF^4₋-activated Gαo₂ and 10 nm AlF^4₋-activated Gαo₁ were applied to permeabilized BON cells measuring either VMAT1 or VMAT2 activity. Note that Gαo₂ downregulates VMATs at concentrations between 0.2 and 2 nmm whereas Gαo₁ had no effect on the activity VMAT2. Values (n = 3 ± SD) are expressed as percent of control of the reserpine-sensitive monoamine uptake, which was 1.86 ± 0.2 and 0.33 ± 0.033 pmol/mg of protein for VMAT1 and VMAT2, respectively. Note that VMAT2 activity is more affected by Gαo₂ between 0.7 and 6 nm than VMAT1 (*p < 0.008; **p < 0.02; ***p < 0.04, calculated by students't test). C, Increasing concentrations of GMppNp between 5 and 100 μm were applied to permeabilized BON cells. VMAT1 or VMAT2 activity was measured. Values (n = 3 ± SD) are expressed as percent of control of the reserpine-sensitive monoamine uptake, which was 1.03 ± 0.02 and 0.53 ± 0.01 pmol/mg of protein for VMAT1 and VMAT2, respectively.