RT Journal Article
SR Electronic
T1 Expression and 1,4-Dihydropyridine-Binding Properties of Brain L-Type Calcium Channel Isoforms
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 407
OP 414
DO 10.1124/mol.108.049981
VO 75
IS 2
A1 Martina J. Sinnegger-Brauns
A1 Irene G. Huber
A1 Alexandra Koschak
A1 Claudia Wild
A1 Gerald J Obermair
A1 Ursula Einzinger
A1 Jean-Charles Hoda
A1 Simone B. Sartori
A1 Jörg Striessnig
YR 2009
UL http://molpharm.aspetjournals.org/content/75/2/407.abstract
AB The L-type calcium channel (LTCC) isoforms Cav1.2 and Cav1.3 display similar 1,4-dihydropyridine (DHP) 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 what extent Cav1.1 and Cav1.4 contribute to L-type-specific DHP binding activity in brain. To address this question and to determine whether DHPs can discriminate between Cav1.2 and Cav1.3 binding pockets, we combined radioreceptor assays and quantitative polymerase chain reaction (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(-/-)]. (+)-[3H]isradipine binding to Cav1.2DHP(-/-) and Cav-DM brains was reduced to 15.1 and 4.4% of wild type, respectively, indicating that Cav1.3 accounts for 10.7% of brain LTCCs. qPCR revealed that Cav1.1 and Cav1.4 α1 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 (+)-[3H]isradipine binding to Cav1.2DHP(-/-) (predominantly Cav1.3) and wild-type (predominantly Cav1.2) brain membranes by unlabeled DHPs revealed a 3- to 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, because of their very low expression, Cav1.1 and Cav1.4 are unlikely to serve as drug targets to treat CNS diseases. The American Society for Pharmacology and Experimental Therapeutics