L-type Ca(2+) channels in mammalian brain neurons have either a Ca(V)1.2 or Ca(V)1.3 pore-forming subunit. Recently, it was shown that Ca(V)1.3 Ca(2+) channels underlie autonomous pacemaking in adult dopaminergic neurons in the substantia nigra pars compacta, and this reliance renders them sensitive to toxins used to create animal models of Parkinson's disease. Antagonism of these channels with the dihydropyridine antihypertensive drug isradipine diminishes the reliance on Ca(2+) and the sensitivity of these neurons to toxins, pointing to a potential neuroprotective strategy. However, for neuroprotection without an antihypertensive side effect, selective Ca(V)1.3 channel antagonists are required. In an attempt to identify potent and selective antagonists of Ca(V)1.3 channels, 124 dihydropyridines (4-substituted-1,4-dihydropyridine-3,5-dicarboxylic diesters) were synthesized. The antagonism of heterologously expressed Ca(V)1.2 and Ca(V)1.3 channels was then tested using electrophysiological approaches and the FLIPR Calcium 4 assay. Despite the large diversity in substitution on the dihydropyridine scaffold, the most Ca(V)1.3 selectivity was only about twofold. These results support a highly similar dihydropyridine binding site at both Ca(V)1.2 and Ca(V)1.3 channels and suggests that other classes of compounds need to be identified for Ca(V)1.3 selectivity.
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