High-affinity antibodies to the 1,4-dihydropyridine Ca2+-channel blockers.

Abstract

Antibodies with affinity and specificity for the 1,4-dihydropyridine Ca2+-channel blockers have been produced in rabbits by immunization with dihydropyridine-protein conjugates. Drugs that block these voltage-dependent Ca2' channels are used for the treatment of various cardiovascular disorders and are referred to as Ca2+-channel blockers (4-8).Nifedipine, nitrendipine, nisoldipine, and related 1,4-dihydropyridines are the most potent class of Ca2+-channel blockers, and radiolabeled dihydropyridines have been shown to bind with high affinity to membranes isolated from cardiac, skeletal, and smooth muscle (9-13). To better understand the mechanism of action of the dihydropyridine Ca2+-channel blockers, investigators have undertaken the identification of the membrane receptor for these drugs in cardiac and skeletal muscle (14-16) and the isolation and purification of the membrane receptor from enriched sources (i.e., transverse tubular membrane of skeletal muscle) (17)(18)(19). Considerable advances have been made in recent years in the structural and functional characterization of membrane receptors and ion channels by using immunological probes (20)(21)(22)(23)(24)(25)(26). Antibodies have been raised against membrane receptors or ion channels directly by immunization with purified membrane proteins or indirectly by immunization with anti-ligand antibodies to produce anti-idiotypic antibodies. Anti-idiotypic antibodies have been very useful in studying receptor structure and function, because these antibodies bind to the ligand binding site on the receptor and in some cases can modify receptor function (21). Anti-ligand antibodies (20,21,23,(26)(27)(28)(29) have been used to study structureactivity relationships between the ligand and antibody and as specific molecules that can compete with the receptor for the ligand.We report here the production of high-affinity antibodies specific for the 1,4-dihydropyridine Ca2+-channel blockers by using either a bovine serum albumin-dihydropyridine conjugate or a keyhole limpet hemocyanin-dihydropyridine conjugate. The dihydropyridine-protein conjugates were prepared by using an affinity analog of nifedipine-1,4-dihydro -2,6 -dimethyl -4 -(2 -isothiocyanatophenyl) -3,5-pyridinedicarboxylic acid dimethyl ester (nifedipine-isothiocyanate)-that can covalently react with free amino groups in both proteins to form a covalent dihydropyridine-protein conjugate. Anti-dihydropyridine antibodies have been found to bind [3H]nitrendipine with high affinity and specificity.The dihydropyridine binding properties of the antidihydropyridine antibodies suggest that the antibodies resemble the membrane receptor for the 1,4-dihydropyridine Ca2+-channel blockers with respect to affinity and specificity of 1,4-dihydropyridine binding. MATERIALS AND METHODSPreparation of Dihydropyridine-Protein Conjugates.Nifedipine-isothiocyanate was used to couple nifedipine covalently to various carrier proteins (i.e., bovine serum albumin, ovalbumin, and keyhole limpet hemocyanin). The carrier protei...

Dystrophin Dp71: The Smallest but Multifunctional Product of the Duchenne Muscular Dystrophy Gene

“…Dystrophin consists of an N-terminal actin-binding domain, a central rod-like domain comprising 24 spectrin-like triple helical coiled coils, and a cysteine-rich C terminus that allows dystrophin to associate with a group of extracellular (α-dystroglycan), integral membrane (sarcoglycans and β-dystroglycan), and cytoplasmic (syntrophins and dystrobrevins) proteins to form the dystrophin-associated protein complex (DAPC) [7][8][9]. Specifically, dystrophin binds to both actin and β-dystroglycan; the extracellular domain of β-dystroglycan binds to α-dystroglycan, which in turns binds to laminin in the extracellular matrix [10].…”