Analysis of L-[3H]-glutamate radioligand binding to plasma membranes of the ampullae of Lorenzini of skates.

Radioligand binding analysis of L-[3H]-glutamate to plasma membranes of the ampullae of Lorenzini in the skate revealed one type of binding site with KD = 286 nM and Bmax = 2.1 pmol mg-1 protein. It was revealed that Na+, K+, Ca2+ and Mg2+ inhibited the L-[3H]-glutamate binding, while Cl- had no effect. The glutamate agonists kainate, quisqualate and N-methyl-D-aspartate (NMDA) were shown to inhibit glutamate binding in a dose-dependent manner. The results obtained confirm the electrophysiological observations suggesting the existence of three types of glutamate receptor at afferent synapses of the ampullae of Lorenzini of skates.