The effect of N-ethylmaleimide on transmitter release from the skeletal neuromuscular junction of Bufo marinus.

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Abstract from Synapse. 2004 Sep;53(3):151-8.

The effect of N-ethylmaleimide on transmitter release from the skeletal

neuromuscular junction of Bufo marinus.

Knight D, Bellingham MC, Lavidis NA.

School of Biomedical Sciences, University of Queensland, St Lucia. QLD,

Australia 4072.

N-ethylmaleimide (NEM) has been used extensively in biochemical assays

as an inhibitor of the NEM sensitive fusion protein (NSF). However,

examination of the effect of NEM on transmitter release in more

physiologically relevant preparations has proved inconclusive. In the

present study, we have examined the effect of low concentrations of NEM

on synaptic transmission in intact nerve-muscle preparations from toads

(Bufo marinus). Under conditions of low transmitter release probability

(0.3 mM calcium, 1 mM magnesium), treatment with NEM (10 microM) caused

a significant increase in the amplitude of stimulus-evoked endplate

potentials (EPPs) and a significant increase in the frequency of

spontaneously occurring miniature EPPS (MEPPS) without affecting the

amplitude of MEPPs. When the calcium concentration in the bath was

raised to 4 mM, 10 microM NEM had no effect on EPP amplitude. Under

these conditions, NEM treatment reduced paired pulse facilitation and

increased depression during stimulus trains. Treatment with NEM also

resulted in a significant decrease in the synaptic delay. The effects of

NEM on transmitter release in the present study were not due to

inactivation of G-proteins. The results of the present study show a

calcium-dependent facilitation of stimulus-evoked transmitter release by

NEM. These results are discussed in terms of the possible sites of NEM

action leading to the observed changes in transmitter release.