H]nitrendipine-antibody complex was 0.06 ± 0.02 nM for an antiserum studied in detail, and ranged from 0.01 to 0.24 nM for all antisera studied. The average dissociation constant determined from rate constants of association (k 1 = 2.7 × 10 5 M -1 s -1 ) and dissociation (k -1 = 1.8 × l0 -4 s -1 ) of [ 3 H]nitrendipinefronianti-dihydropyridine antibodies immobilized on Protein-A Sepharose was 0.66 nM Inhibition of [ 3 H]nitrendipine binding was specific for the 1,4-dihydropyridine Ca 2+ channel modifiers, and the concentrations required for half-maximal inhibition ranged between 0.25 and 0.90 nM; structurally unrelated Ca 2+ channel antagonists did not modify [ 3 H]nitrendipine binding to the anti-dihydropyridine antibodies. In summary, anti-dihydropyridine antibodies have been shown to have high affinity and specificity for the 1,4-dihydropyridine Ca 2+ channel antagonists and to exhibit dihydropyridine binding properties similar to the membrane receptor for the 1,4-dihydropyridine Ca 2+ channel antagonists.