The excitatory actions of kainic acid and some derivatives at the crab neuromuscular junction

The actions of kainic acid and its derivatives including the new tricarboxylic kainic acid were tested on the Hermit crab neuromuscular junction. Kainic acid had a direct excitatory effect producing a depolarization. Although not so potent, alpha-ketokainic acid and tricarboxylic kainic acid mimicked this effect whilst dihydrokainic acid did not. The slopes of the dose-response curves for these kainic acid analogues differed from that of L-glutamate. A Hill coefficient approximating one was obtained for kainic acid compared to a value of three for L-glutamate. Threshold concentrations of l-glutamate and kainic acid but not alpha-ketokainic acid and tricarboxylic kainic acid potentiated the neurally evoked excitatory junction potentials and the ionophoretic L-glutamate potential. The results indicate a possible interaction of the kainic acid derivatives with a heterogeneous receptor population and provide a comparison with other invertebrate and vertebrate systems.