Subcellular localization of bioactive cholecystokinin-like peptides in the rat cerebral cortex

The subcellular distribution of cholecystokinin (CCK), especially its exact localization within the synaptosome, was studied in the rat cerebral cortex. Highest CCK-like bioactivity was measured in the synaptic membrane fractions, paralleling the distribution of (Na+ + K+)-dependent ATPase. In the synaptic vesicles, which were characterized by high acetylcholine content and by the absence of (Na+ + K+)-ATPase, only minimal quantities of CCK were detected.