Reserpine labels the catecholamine transporter in synaptic vesicles from bovine caudate nucleus.

Tritiated reserpine binds to synaptic vesicles from bovine caudate with high affinity (Kappd = 1.25 nM, Bmax = 3.3 pmol/mg protein). This interaction is both ATP-dependent and sensitive to the protonophores CCCP and nigericin, suggesting that a proton electrochemical gradient is required for binding. Dopamine, epinephrine, norepinephrine and serotonin all inhibit reserpine binding at concentrations similar to those required for inhibition of dopamine uptake. Treatment with saponin to release vesicle contents results in complete loss of accumulated dopamine but retention of bound reserpine. These results indicate that reserpine binds to the catecholamine transport system of synaptic vesicles with high affinity and specificity.