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

Area of Science:

• Neuroscience
• Biochemistry
• Pharmacology

Background:

• Synaptic vesicles store neurotransmitters like dopamine and serotonin.
• Reserpine is a known inhibitor of monoamine transporters.
• Understanding reserpine's interaction with synaptic vesicles is crucial for neuroscience research.

Purpose of the Study:

• To investigate the binding characteristics of tritiated reserpine to synaptic vesicles.
• To determine the dependence of reserpine binding on ATP and proton gradients.
• To elucidate the specificity of reserpine binding to the catecholamine transport system.

Main Methods:

• Using tritiated reserpine to assess binding affinity (Kappd) and capacity (Bmax) in bovine caudate synaptic vesicles.
• Investigating the role of ATP and proton electrochemical gradients using protonophores (CCCP, nigericin).
• Assessing the inhibitory effects of dopamine, epinephrine, norepinephrine, and serotonin on reserpine binding.

Main Results:

• Tritiated reserpine exhibited high-affinity binding to synaptic vesicles (Kappd = 1.25 nM, Bmax = 3.3 pmol/mg protein).
• Reserpine binding was dependent on ATP and a proton electrochemical gradient, sensitive to CCCP and nigericin.
• Neurotransmitters (dopamine, epinephrine, norepinephrine, serotonin) inhibited reserpine binding, similar to their effect on dopamine uptake.
• Saponin treatment released vesicle contents but retained bound reserpine.

Conclusions:

• Reserpine binds with high affinity and specificity to the synaptic vesicle catecholamine transporter.
• The binding process is dependent on the vesicle's proton electrochemical gradient.
• These findings clarify reserpine's mechanism of action at the synaptic vesicle level.