Phylogenetic studies on the synaptic vesicle glutamate transport system

Area of Science:

• Neuroscience
• Biochemistry
• Evolutionary Biology

Background:

• Vesicular glutamate uptake in mammalian brains is ATP-dependent, requires a proton gradient, is chloride-stimulated, and glutamate-specific.
• The fundamental nature of these characteristics in the vesicular uptake system across diverse species was previously unknown.

Purpose of the Study:

• To investigate the conservation of key glutamate uptake characteristics in synaptic vesicles across vertebrate and invertebrate species.
• To determine if the observed mammalian glutamate uptake properties are fundamental to the vesicular transport system.

Main Methods:

• Synaptic vesicles were isolated from the brains and central nervous ganglia of various vertebrate (goldfish, frogs, turtles, pigeons, rats) and invertebrate (Drosophila, crayfish) species.
• Glutamate uptake activity was assayed in these isolated vesicles, examining ATP dependence, substrate specificity, chloride stimulation, and energy source (V-type ATPase).

Main Results:

• ATP-dependent glutamate uptake was detected in all tested vertebrate species but not in invertebrates (Drosophila, crayfish).
• Vertebrate vesicles exhibited conserved characteristics: high glutamate specificity, V-type ATPase energization, significant chloride stimulation (3-6 fold), and a glutamate Km of 0.5-2 mM.
• Minor variations were observed in glutamate specificity, vesicle glutamate levels, and Vmax across vertebrate species.

Conclusions:

• The synaptic vesicle glutamate uptake system is a conserved feature throughout the vertebrate lineage.
• Major functional aspects, including chloride stimulation and strict substrate specificity, have remained stable for over 350-400 million years, indicating strong evolutionary conservation.