High affinity interaction of mibefradil with voltage‐gated calcium and sodium channels

• Published in: British journal of pharmacology Vol. 130; no. 3; pp. 669 - 677
• Main Authors: Eller, Philipp, Berjukov, Stanislav, Wanner, Siegmund, Huber, Irene, Hering, Steffen, Knaus, Hans‐Günther, Toth, Geza, Kimball, S David, Striessnig, Jörg
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.06.2000; Nature Publishing
• Subjects: Animals; Biological and medical sciences; Ca2+ channel blockers; Calcium Channel Blockers - pharmacology; Calcium Channels, L-Type - drug effects; Cardiovascular system; Electric Stimulation; Electrophysiology; Guinea Pigs; In Vitro Techniques; Ion Channel Gating - drug effects; Medical sciences; mibefradil; Mibefradil - pharmacology; Miscellaneous; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; Patch-Clamp Techniques; Pharmacology. Drug treatments; Rabbits; Radioligand Assay; Sodium Channel Blockers; Mibefradil; Rodentia; Calcium antagonist; Central nervous system; Rabbit; Ionic channel; Lagomorpha; Striated muscle; In vitro; Vertebrata; Biological fixation; Mammalia; Calcium ion; Guinea pig; Animal; Plasma membrane; Sodium ion; Brain (vertebrata)
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0703352

Mibefradil is a novel Ca2+ antagonist which blocks both high‐voltage activated and low voltage‐activated Ca2+ channels. Although L‐type Ca2+ channel block was demonstrated in functional experiments its molecular interaction with the channel has not yet been studied. We therefore investigated the binding of [3H]‐mibefradil and a series of mibefradil analogues to L‐type Ca2+ channels in different tissues. [3H]‐Mibefradil labelled a single class of high affinity sites on skeletal muscle L‐type Ca2+ channels (KD of 2.5±0.4 nM, Bmax=56.4±2.3 pmol mg−1 of protein). Mibefradil (and a series of analogues) partially inhibited (+)‐[3H]‐isradipine binding to skeletal muscle membranes but stimulated binding to brain L‐type Ca2+ channels and α1C‐subunits expressed in tsA201 cells indicating a tissue‐specific, non‐competitive interaction between the dihydropyridine and mibefradil binding domain. [3H]‐Mibefradil also labelled a heterogenous population of high affinity sites in rabbit brain which was inhibited by a series of nonspecific Ca2+ and Na+‐channel blockers. Mibefradil and its analogue RO40‐6040 had high affinity for neuronal voltage‐gated Na+‐channels as confirmed in binding (apparent Ki values of 17 and 1.0 nM, respectively) and functional experiments (40% use‐dependent inhibition of Na+‐channel current by 1 μM mibefradil in GH3 cells). Our data demonstrate that mibefradil binds to voltage‐gated L‐type Ca2+ channels with very high affinity and is also a potent blocker of voltage‐gated neuronal Na+‐channels. More lipophilic mibefradil analogues may possess neuroprotective properties like other nonselective Ca2+‐/Na+‐channel blockers. British Journal of Pharmacology (2000) 130, 669–677; doi:10.1038/sj.bjp.0703352