Effects of a hydroxy-cinnamoyl conjugate of spermidine on arthropod neuromuscular junctions

N1-coumaroyl spermidine is structurally similar to acylpolyamines found in spider and wasp venoms, which are known to block arthropod glutamate receptors. N1-coumaroyl spermidine reduced the amplitude of excitatory postsynaptic potentials recorded in crayfish muscle. This effect was dose dependent, with an IC50 value of 70 micromol l(-1). N1-coumaroyl spermidine reversibly reduced the amplitude of potentials elicited by iontophoretic application of L-glutamate, indicating a direct effect on postsynaptic glutamate receptors. Neither 1 mmol l(-1) spermidine nor 1 mmol l(-1) coumaric acid altered excitatory postsynaptic potential amplitude, indicating that blockage requires the conjugated phenolic polyamine. N1-coumaroyl spermine, a slightly longer phenolic polyamine, reduced excitatory postsynaptic potential amplitude with approximately the same potency as N1-coumaroyl spermidine. Thus, potency of blockage does not appear to be affected in this experimental preparation by small changes in length of the polyamine. N1-coumaroyl spermidine also reduced excitatory postsynaptic potentials in muscles of the insect Drosophila. The ability of N1-coumaroyl spermidine to attenuate synaptic transmission at insect neuromuscular synapses lends support to the notion that plant-derived phenolic polyamines might serve as natural insecticides.