A pharmacological and HPLC analysis of the excitatory transmitter of the cardiac ganglion in the heart of the isopod crustacean Bathynomus doederleini.

In crustacean neurogenic hearts, the myocardium contracts under the tight control of rhythmically active neurons of the cardiac ganglion located inside the heart. We demonstrated that the myocardium of Bathynomus doederleini was sensitive to glutamate, quisqualate, and kainate, and that the tension of myocardial cells developed in a dose-dependent manner. The threshold concentrations were 10(-5) M for quisqualate, 10(-4) M for glutamate, and 3 x 10(-4) M for kainate. Concanavalin A, known to prevent desensitization of glutamate receptors at crustacean neuromuscular junctions, augmented excitatory junctional potentials evoked by the cardiac ganglionic neurons in myocardial cells. Using a high performance liquid chromatography (HPLC), we analyzed glutamate in extracts of the cardiac ganglion and myocardium. We obtained values for glutamate concentrations, 8741.2 +/- 184.2 and 678.2 +/- 10.7 pmol/mg, respectively. Although we attempted to measure monoamines in the extracts by HPLC, these were not detected at measurable (more than 1 fmol per 10-microL sample) levels. In conclusion, myocardial cells in isopod crustaceans were suggested to receive glutamatergic motor innervation.