Abstract
The binding properties of the 1,4-dihydropyridine calcium channel antagonist, [ 3H]( +)PN 200-110, were studied in rat cerebral cortical and cardiac homogenates (37°C, Krebs phosphate buffer). Specific binding of [ 3H]( +)PN 200-110 was saturable, reversible, and of high affinity (K d values are 35 and 64 pM for the cerebral cortex and heart, respectively). In parallel studies with [ 3H]( +)PN 200-110, the dissociation constant of [ 3H]nitrendipine was 10–12 times higher. Substituted dihydropyridine calcium channel antagonists and agonists competitively inhibited specific [ 3H]( +)PN 200-110 binding, but d-cis diltiazem enhanced and verapamil incompletely inhibited [ 3H]( +)PN 200-110 binding in both the cerebral cortex and the heart. The effects of diltiazem and verapamil on [ 3H]( +)PN 200-110 binding were due mainly to alterations in the dissociation constant (K d), without alterations in the binding density (B max). The new [ 3H]( +)PN 200-110 receptor binding assay is remarkable for its low degree of nonspecific binding as compared to [ 3H]nitrendipine at physiological temperatures. [ 3H( +)PN 200-110 is a useful ligand for the further analysis of the dihydropyridine binding sites associated with calcium channels.
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