Expression and 1,4-dihydropyridine-binding properties of brain L-type calcium channel isoforms. Molecular pharmacology [Mol Pharmacol] Journal article

The L-type calcium channel (LTCC) isoforms Cav1.2 and Cav1.3 display similar 1,4-Dihydropyridine binding properties and are both expressed in mammalian brain. Recent work implicates Cav1.3 channels as interesting drug targets, but no isoform selective modulators exist. It is also unknown to which extent Cav1.1 and Cav1.4 contribute to L-type specific dihydropyridine (DHP) binding activity in brain. To address this question and to determine if DHPs can discriminate between Cav1.2 and Cav1.3 binding pockets we combined radioreceptor assays and quantitative PCR (qPCR). We bred double mutants (Cav-DM) from mice expressing mutant Cav1.2 channels (Cav1.2DHP(-/-)) lacking high affinity for DHPs and from Cav1.3 knockouts (Cav1.3(-/-)). (+)-[(3)H]isradipine binding to Cav1.2DHP(-/-) and Cav-DM brains was reduced to 15.1 and 4.4% of wildtype, respectively, indicating that Cav1.3 accounts for 10.7% of brain LTCCs. qPCR revealed that Cav1.1 and Cav1.4 alpha1 subunits comprised 0.08% of the LTCC transcripts in mouse whole brain, suggesting that they cannot account for the residual binding. Instead, this could be explained by low affinity binding (127-fold Kd increase) to the mutated Cav1.2 channels. Inhibition of (+)-[(3)H]isradipine binding to Cav1.2DHP(-/-) (predominantly Cav1.3) and wildtype (predominantly Cav1.2) brain membranes by unlabeled DHPs revealed a 3-4-fold selectivity of nitrendipine and nifedipine for the Cav1.2 binding pocket, a finding further confirmed with heterologously expressed channels. This suggests that small differences in their binding pockets may allow development of isoform-selective modulators for LTCCs and that, due to their very low expression, Cav1.1 and Cav1.4 are unlikely to serve as drug targets to treat CNS diseases.

Molecular pharmacology [Mol Pharmacol]