From neurochemical lesion studies performed in rat caudate nucleus and in hippocampus, it appears that dihydropyridine- sensitive voltage-dependent calcium channels are mainly localized on intrinsic neurons and are only sparingly present or absent on nerve endings emanating from other brain areas. 3H-Nitrendipine binds preferentially to a subpopulation of synaptosomes enriched in postsynaptic membrane fractions purified by Percoll gradient. Endogenous ligand (EL) for 3H-nitrendipine binding sites has been isolated from rat brain: EL decreases the specific binding of 3H-nitrendipine; it inhibits 45Ca2+ uptake mediated by voltage-sensitive or glutamate receptor-operated Ca2+ channels; it decreases the veratridine- elicited c-GMP formation and reverses the enhancement of 3H- Phorbol-12, 13-dibutyrate binding after stimulating by veratridine, glutament or kainate.
