Glutamate and N-methyl-D-aspartate affect release from crayfish axon terminals in a voltage-dependent manner.
In the crayfish neuromuscular junction, the excitatory transmitter is glutamate. The present study shows that at concentrations as low as 5 x 10(-7) M, glutamate affects the depolarization-evoked release of neurotransmitter. Furthermore, the effect of glutamate on release is voltage-dependent and depends on the level of the depolarizing pulse. Nerve terminals were exposed to 5 x 10(-7) M tetrodotoxin and then depolarized to different levels by a macropatch electrode. Depending on the amplitude of the depolarizing pulse, glutamate (5 x 10(-7) to 1 x 10(-5) M) had a dual effect on release. At small depolarizing pulses, glutamate reduced release, whereas at large depolarizing pulses, it enhanced it. Glutamate at 10(-6) M had no significant effect on action-potential-induced release. At 10(-4) M glutamate, the action-potential-induced release was always inhibited. N-Methyl-D-aspartate was found to mimic one of the effects of glutamate: N-methyl-D-aspartate (10(-7) to 10(-5) M) reduced release at small depolarizing pulses but had no effect with larger depolarizations. 2-Amino-5-phosphonovaleric acid blocked the effect of N-methyl-D-aspartate.
Otto Loewi Center for Cellular and Molecular Neurobiology, Hebrew University of Jerusalem, Israel.
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H
Parnas
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Parnas
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Ravin
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Yudelevitch
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003400:Astacoidea / Q000502:physiology; D001369:Axons; D002118:Calcium / Q000378:metabolism; D005971:Glutamates / Q000008:administration & dosage*; D008274:Magnesium / Q000378:metabolism; D008564:Membrane Potentials; D016202:N-Methylaspartate / Q000008:administration & dosage*; D009431:Neural Conduction / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects*
D005971:Glutamates; D018377:Neurotransmitter Agents; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; D008274:Magnesium; D002118:Calcium