AUTORADIOGRAPHIC LOCALIZATION OF [I-125] CHARYBDOTOXIN BINDING-SITES IN RAT-BRAIN

Charybdotoxin, a 37 amino acid peptide isolated from scorpion venom, is a potent inhibitor of potassium channel function. [I-125]charybdotoxin was originally believed to be a selective ligand for the Ca2+-sensitive channel in many tissues, but it appears to bind only to a voltage-sensitive potassium channel in brain. We found high densities of [I-125]charybdotoxin binding in the lateral olfactory tract, interpeduncular nucleus and a variety of mesencephalic nuclei. Moderate levels were found in the cerebral cortex, medial thalamus, hypothalamus and selected thalamic nuclei. These results indicate that [I-125]charybdotoxin identifies a potassium channel or channels with a unique distribution in the brain.