Different target sizes of the voltage-dependent Ca super(2+) channel and the ( super(3)H)nitrendipine binding site in rat brain

High energy irradiation of frozen rat frontal cortex was used to determine the molecular target sizes of the ( super(3)H)nitrendipine binding site (93,500 plus or minus 9,700 daltons and of the voltage-dependent Ca super(2+) channel (340,500 plus or minus 34,000 daltons) determined as the K super(+)-induced super(45)Ca super(2+) uptake into synaptosomes. The conclusion that could be drawn from the target size analysis was that super(45)Ca super(2+) flux occurs via a structure of molecular weight very different from that of the dihydropyridine binding site. Furthermore, it was found that ( super(3)H)nitrendipine binding to synaptosomes was not influenced by depolarization with K super(+).