Isolation of Neurogenic and Myogenic Activities by Joro Spider Toxin in the Adult Heart of the Isopod Crustacean Ligia exotica

Abstract

The effects of Joro spider toxin (JSTX), a specific glutamate antagonist, on the adult heart of the isopod crustacean Ligia exotica were examined. By application of JSTX, excitatory junctional potentials (EJPs) caused by the cardiac ganglion activity in the myocardium were gradually abolished. Subsequently, the cardiac ganglion and myocardium exhibited independent activities with their respective rhythms. In saline containing JSTX, no changes were observed in the muscle activity when the ganglionic activity was changed by current injection into the cardiac ganglion neuron. These results indicate that two pacemaker sites, the cardiac ganglion and cardiac muscle, are present in the adult heart of Ligia exotica and suggest glutamatergic neuromuscular transmission between them.