We report the synthesis of the single enantiomers of permanently charged dihydropyridine derivatives (DHPs with alkyl linker lengths of two and eight carbon atoms) and their activities on cardiac and neuronal L-type calcium channels. Permanently charged chiral 1,4-dihydropyridines and methyl (omega)-trimethylalkylammonium) 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylate iodides were synthesized in high optical purities from (R)-(-) and (S)-(+)-1,4-dihydro-2,6-dimethyl-5-methoxycarbonyl-4-(3-nitrophenyl)-3-+ ++pyridinecarboxylic acid, obtained by resolution of racemic 1,4-dihydro-2,6-dimethyl-5-methoxycarbonyl-4-(3-nitrophenyl)-3-pyridi necarboxylic acid. Competition binding experiments with radioligand [3H]-(+)-PN200-110 and the block of whole cell barium currents through L-type calcium channels in GH4C1 cells show that the compounds with the eight-carbon alkyl linker optimally block the L-type Ca2+ channels, and that the S-enantiomer is more potent than the R-enantiomer.

Kv␤2 enhances the rate of inactivation and level of expression of Kv1.4 currents. The crystal structure of Kv␤2 binds NADP ؉ , and it has been suggested that Kv␤2 is an oxidoreductase enzyme (1). To investigate how this function might relate to channel modulation, we made point mutations in Kv␤2 in either the NADPH docking or putative catalytic sites. Using the yeast two-hybrid system, we found that these mutations did not disrupt the interaction of Kv␤2 with Kv␣1 channels. To characterize the Kv␤2 mutants functionally, we coinjected wild-type or mutant Kv␤2 cRNAs and Kv1.4 cRNA in Xenopus laevis oocytes. Kv␤2 increased both the amplitude and rate of inactivation of Kv1.4 currents. The cellular content of Kv1.4 protein was unchanged on Western blot, but the amount in the plasmalemma was increased. Mutations in either the orientation or putative catalytic sites for NADPH abolished the expressionenhancing effect on Kv1.4 current. Western blots showed that both types of mutation reduced Kv1.4 protein. Like the wild-type Kv␤2, both types of mutation increased the rate of inactivation of Kv1.4, confirming the physical association of mutant Kv␤2 subunits with Kv1.4. Thus, mutations that should interfere with NADPH function uncouple the expression-enhancing effect of Kv␤2 on Kv1.4 currents from its effect on the rate of inactivation. These results suggest that the binding of NADPH and the putative oxidoreductase activity of Kv␤2 may play a role in the processing of Kv1.4.

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Nifedipine analogs I, II and III with the 2H‐1‐benzopyran‐2‐one (coumarin) fluorophore linked at the 2, 2 and 6 and 4 positions of the dihydropyridine ring were synthesized by the modified Hantzch condensation procedures. Attempts to synthesize dihydropyridine with the fluorophore at position 3 (IV) were unsuccessful.

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