CA2-SENSITIVE AND INSENSITIVE OMEGA-CONOTOXIN GVIA BINDING-SITES IN RAT-BRAIN()

THE autoradiographic distribution of Ca2+-sensitive high-and low-affin ity binding sites for the N-type calcium channel ligand, [125]omega-co notoxin GVIA, has been examined in rat brain. Both classes of sites we re rather evenly distributed, exhibiting their highest density in cell body rich layers, such as the pyramidal layer of Ammon's horn and the granular layer of the dentate gyrus. In cerebellum, the granular laye r was more densely labelled than the molecular layer at low ligand con centration, and this pattern was reversed at high concentration. The p resence of 30 mM Ca2+ in the incubation medium revealed the existence of a third class of sites, insensitive to Ca2+, comparably distributed at both concentrations, and apparently absent from cell body rich lay ers.