Identification of Voltage Operated Calcium Channels by Binding Studies: Differentiation of Subclasses of Calcium Antagonist Drugs with3H-Nimodipine Radioligand Binding
- 1 January 1983
- journal article
- research article
- Published by Taylor & Francis in Journal of Receptor Research
- Vol. 3 (1-2) , 177-190
- https://doi.org/10.3109/10799898309041932
Abstract
3H-Nimodipine (3H -NIM) is a high affinity radioligand suitable to study Ca2+ -channels in a variety of tissues. The binding is saturable, reversible, and stereospecific in purified bovine heart and partially purified guinea-pig brain membranes. In the latter a Bmax of 600fmol/mg protein, dissociation constants (KD) of 0.4-0.8nM and a Hill slope of 1.0 are found. At 37C the optimal pH in 50mM TRIS-HCl buffer is 7.1-7.4. The calcium channel is a metalloprotein, and the divalent cation which is essential for the binding of 3 H -NIM can be removed by EDTA (EC50 20μM); the nimodipine binding site of the channel may then be reconstituted by divalent cations with Mn2+ > Ca2+>Mg2+>Sr2+. Ca2+-antagonist drugs can be divided into three main classes based on their interaction with the 3H -NIM binding site: Class I has one site law of mass action-displacement isotherms with 3H -NIM, Class II exhibits complex biphasic inhibition profiles and Class III drugs increase the affinity of 1,4 dihydropyridines for the Ca2+ -channel. Diltiazem is a Class III Ca2+ -antagonist. Our in vitro studies lead us to conclude that the Ca2+ -channel contains multiple regulatory sites at which drugs can act.Keywords
This publication has 6 references indexed in Scilit:
- Calcium and potassium currents in muscle fibres of an insect (Carausius morosus).The Journal of Physiology, 1982
- Binding characteristics of (+)-, (±)- and (-)-[125Iodo] cyanopindolol to guinea-pig left ventricle membranesNaunyn-Schmiedebergs Archiv für experimentelle Pathologie und Pharmakologie, 1982
- Adenosine receptor agonists: Binding and adenylate cyclase stimulation in rat liver plasma membranesNaunyn-Schmiedebergs Archiv für experimentelle Pathologie und Pharmakologie, 1982
- Interactions of magnesium and verapamil on tone and contractility of vascular smooth muscleEuropean Journal of Pharmacology, 1981
- Sodium-calcium ion exchange in cardiac membrane vesicles.Proceedings of the National Academy of Sciences, 1979
- Inotropic and electrophysiological actions of verapamil and D 600 in mammalian myocardiumNaunyn-Schmiedebergs Archiv für experimentelle Pathologie und Pharmakologie, 1975