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The glutamate transporter EAAT5 works as a presynaptic receptor in mouse rod bipolar cells
Author(s) -
Wersinger Eric,
Schwab Yannick,
Sahel JoséAlain,
Rendon Alvaro,
Pow David V.,
Picaud Serge,
Roux Michel J.
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2006.118281
Subject(s) - biophysics , inhibitory postsynaptic potential , glutamate receptor , cnqx , excitatory postsynaptic potential , chemistry , postsynaptic potential , reversal potential , biology , neuroscience , biochemistry , patch clamp , ampa receptor , receptor
Membrane neurotransmitter transporters control the concentration of their substrate in the synaptic clefts, through the thermodynamic coupling of uptake to the movement of Na + and other ions. In addition, excitatory amino acid transporters (EAAT) have a Cl − conductance which is gated by the joint binding of Na + and glutamate, but thermodynamically uncoupled to the flux of glutamate. This conductance is particularly large in the retina‐specific EAAT5 isoform. In the mouse retina, we located EAAT5 in both cone and rod photoreceptor terminals and in axon terminals of rod bipolar cells. In these later cells, application of glutamate on the axon terminal evoked a current that reversed at E Cl , was insensitive to bicuculline, TPMPA, strychnine, dl ‐AP5, CNQX and MCPG, but blocked by the glutamate transporter inhibitor dl ‐tBOA. Furthermore, short depolarizations of the bipolar cells evoked a dl ‐tBOA and Cd 2+ ‐sensitive current whose amplitude was comparable to the glutamate‐evoked current. Its kinetics indicated that EAAT5 was located close to the glutamate release site. For 2 ms depolarizations evoking maximal responses, the EAAT5‐mediated current carried between 2 and 8 times more charge as an average inhibitory GABA or glycine postsynaptic current received spontaneously from amacrine cells, with 10 m m or 0.5 m m intracellular EGTA, respectively. In conditions for which reciprocal inhibition could be monitored, the charge carried by the EAAT5 current was 1.5 times larger than the one carried by the inhibitory postsynaptic currents received from amacrine cells. These results indicate that EAAT5 acts as a major inhibitory presynaptic receptor at mammalian rod bipolar cell axon terminals. This feedback mechanism could control glutamate release at the ribbon synapses of a non‐spiking neuron and increase the temporal contrast in the rod photoreceptor pathway.