Different target sizes of the voltage-dependent Ca2+ channel and the [3H]nitrendipine binding site in rat brain

High energy irradiation of frozen rat frontal cortex was used to determine the molecular target sizes of the [3H]nitrendipine binding site (93,500 +/- 9,700 daltons and of the voltage-dependent Ca2+ channel (340,500 +/- 34,000 daltons) determined as the K+-induced 45Ca2+ uptake into synaptosomes. The conclusion that could be drawn from the target size analysis was that 45Ca2+ flux occurs via a structure of molecular weight very different from that of the dihydropyridine binding site. Furthermore, it was found that [3H]nitrendipine binding to synaptosomes was not influenced by depolarization with K+.