The possibility that L-glutamate is the excitatory transmitter at the Drosophila larval neuromuscular junction and the ionic basis of its action on the muscle membrane are examined. 2. Iontophoretically applied L-glutamate causes muscle depolarization (L-glutamate potential) if and only if the L-glutamate pipette is within a few mum of the nerve ending. D-glutamate, substance P, ACh and GABA are ineffective. 3. Bath-applied L-glutamate produces similar changes in the time course and amplitude of miniature excitatory junctional potential (m.e.j.p.), excitatory junctional potential (e.j.p.) and the L-glutamate potential. 4. Neuromuscular transmission and excitation-contraction coupling are operative in a haemolymph-like solution containing 1 mM L-glutamate. 5. The reversal potentials of the e.j.p. and the L-glutamate potential are identical to each other, changing similarly with changes in the ionic compositions of the external medium (twelve solutions). 6. The ionic dependence of the reversal potentials is predicted from an extended constant-field equation using a ratio of sodium:potassium permeabilities of PNa/PK=1-3, and a ratio of magnesium:potassium permeabilities of PMg/PK=4-7. 7. It is concluded that L-glutamate is, or is an agonist of, the excitatory transmitter at certain Drosophila larval neuromuscular junctions.

L-glutamate as an excitatory transmitter at the Drosophila larval neuromuscular junction.

Organization and synaptic physiology of crustacean neuromuscular systems

Identified neurons and behavior of arthropods

Spider toxins as tools for dissecting elements of excitatory amino acid transmission

Amino acids as neurotransmitters.

THERE is considerable evidence that L-glutamate is the excitatory transmitter both at the insect and crustacean neuromuscular junction1,2, and also in the vertebrate central nervous system3. Here we report the use of the voltage clamp technique to compare the reversal potentials of the conductance increase produced by the excitatory transmitter and the application of L-glutamate at the insect neuromuscular junction. We also investigated the ionic basis of the L-glutamate conductance increase using voltage clamping. These experiments could be carried out accurately because changes in resistance of the electrically excitable membrane caused by changes in membrane potential or by different ionic media do not affect the amplitude of the excitatory junctional currents or glutamate currents.

R. Anwyl

Papers

Voltage clamp studies of glutamate synapse