Release of exogenously supplied [3H]glutamate and endogenous glutamate from tissue slices of the cestode Hymenolepis diminuta.

The effect of high potassium depolarization on the release of exogenously supplied [3H]glutamate and endogenous glutamate from tissue slices of the cestode Hymenolepis diminuta was examined. Increasing concentrations of potassium stimulated the release of radiolabel from tissues preloaded with [3H]glutamate. This release was by a partially calcium-dependent, magnesium-antagonized process. In the presence of tetrodotoxin, or absence of sodium, release of radiolabel was depressed, presumably by blockade of sodium-dependent neuronal potentials. The release of glutamate of both exogenous and endogenous origin was specifically and significantly elevated by high potassium; glutamate release was significantly depressed in calcium-free saline. The release of other amino acids of endogenous origin, including aspartate, was not elevated by high potassium. Collectively the data provide strong evidence for glutamate to be viewed as the only acidic amino acid neurotransmitter candidate in the cestodes.