Positive heterotropic allosteric regulators of dihydropyridine binding increase the Ca2+ affinity of the L-type Ca2+ channel. Stereoselective reversal by the novel Ca2+ antagonist BM 20.1140.
The alpha 1-subunit of the voltage-dependent L-type Ca2+ channel has distinct, allosterically coupled binding domains for drugs from different chemical classes (dihydropyridines, benzothiazepines, phenylalkylamines, diphenylbutylpiperidines). (-)-BM 20.1140 (ethyl-2,2-di-phenyl-4-(1-pyrrolidino)-5-(2-picolyl)- oxyvalerate) is a novel Ca2+ channel blocker which potently stimulates dihydropyridine binding (K0.5 = 2.98 nM) to brain membranes. This property is shared by (+)-cis-diltiazem, (+)-tetrandrine, fostedil and trans-diclofurime, but (-)-BM 20.1140 does not bind in a competitive manner to the sites labeled by (+)-cis-[3H]diltiazem. (+)-cis-Diltiazem and (-)-BM 20.1140 have differential effects on the rate constants of dihydropyridine binding. (+)-BM 20.1140 reverses the stimulation of the positive allosteric regulators (pA2 value for reversal of (-)-BM 20.1140 stimulation = 7.4, slope 0.72). The underlying molecular mechanism of the potentiation of dihydropyridine binding has been clarified. The K0.5 for free Ca2+ to stabilize a high affinity binding domain for dihydropyridines on purified L-type channels from rabbit skeletal muscle is 300 nM. (+)-Tetrandine (10 microM) increases the affinity 8-fold (K0.5 for free Ca2+ = 30.1 nM) and (+)-BM 20.114 (10 microM) inhibits the affinity increase (K0.5 for free Ca2+ = 251 nM). Similar results were obtained with membrane-bound Ca(2+)-channels from brain tissue which have higher affinity for free Ca2+ (K0.5 for free Ca2+ = 132 nM) and for dihydropyridines compared with skeletal muscle. It is postulated that the dihydropyridine and Ca(2+)-binding sites are interdependent on the alpha 1-subunit, that the different positive heterotropic allosteric regulators (by their differential effects on Ca2+ rate constants) optimize coordination for Ca2+ in the channel pore and, in turn, increase affinity for the dihydropyridines.
Staudinger
R
R
Institute for Biochemical Pharmacology, University of Innsbruck, Austria.
Knaus
H G
HG
Glossmann
H
H
D000470:Alkaloids / Q000494:pharmacology; D000494:Allosteric Regulation; D000818:Animals; D052160:Benzothiazoles; D044182:Benzylisoquinolines; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D004110:Diltiazem / Q000378:metabolism* / Q000494:pharmacology; D006168:Guinea Pigs; D007536:Isomerism; D017275:Isradipine; D007700:Kinetics; D046911:Macromolecular Substances; D008962:Models, Theoretical; D009132:Muscles / Q000378:metabolism*; D010069:Oxadiazoles / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology*; D011759:Pyrrolidines / Q000494:pharmacology*; D011817:Rabbits; D013844:Thiazoles / Q000494:pharmacology*; D014700:Verapamil / Q000031:analogs & derivatives* / Q000378:metabolism
D000470:Alkaloids; D052160:Benzothiazoles; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D046911:Macromolecular Substances; D010069:Oxadiazoles; D011725:Pyridines; D011759:Pyrrolidines; D013844:Thiazoles; C069138:BM 20.1140; C009438:tetrandrine; C043184:4-desmethoxyverapamil; D014700:Verapamil; C035950:fosfedil; D004110:Diltiazem; D002118:Calcium; D017275:Isradipine