Zahradníková Alexandra, Minarovic Igor, Zahradník Ivan
Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlárska 5, 833 34 Bratislava, Slovak Republic.
J Pharmacol Exp Ther. 2007 Aug;322(2):638-45. doi: 10.1124/jpet.107.122176. Epub 2007 May 2.
Phenylalkylamines, benzothiazepines, and dihydropyridines bind noncompetitively to the L-type calcium channel. The molecular mechanisms of this interaction were investigated in enzymatically isolated rat ventricular myocytes using the whole-cell patch-clamp technique. When applied alone, felodipine, verapamil, and diltiazem inhibited the L-type calcium current with values of inhibitory constant (K(B)) of 11, 246, and 512 nM, respectively, whereas 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-[trifluoromethyl]phenyl)-3-pyridine carboxylic acid methyl ester (Bay K8644) activated I(Ca) with activation constant (K(A)) of 33 nM. Maximal activation of I(Ca) by 300 nM Bay K8644 strongly reduced the inhibitory potency of felodipine (apparent K(B) of 165 nM), significantly reduced the inhibitory potency of verapamil (apparent K(B) of 737 nM), but significantly increased the inhibitory potency of diltiazem (apparent K(B) of 310 nM). In terms of a new pseudoequilibrium two-drug binding model, the interaction between the dihydropyridine agonist Bay K8644 and the antagonist felodipine was found purely competitive. The interaction between Bay K8644 and verapamil or diltiazem was found noncompetitive, and it could be described only by inclusion of a negative interaction factor nu = -0.60 for verapamil and a positive interaction factor nu = +0.24 for diltiazem. These results suggest that at physiological membrane potentials, the L-type calcium channel cannot be simultaneously occupied by a dihydropyridine agonist and antagonist, whereas it can simultaneously bind a dihydropyridine agonist and a nondihydropyridine antagonist. Generally, the effects of the drugs on the L-type calcium channel support a concept of a channel domain responsible for binding of calcium channel antagonists and agonists changing dynamically with the membrane voltage and occupancy of individual binding sites.
苯烷基胺类、苯并硫氮䓬类和二氢吡啶类药物与L型钙通道非竞争性结合。利用全细胞膜片钳技术在酶分离的大鼠心室肌细胞中研究了这种相互作用的分子机制。单独应用时，非洛地平、维拉帕米和地尔硫䓬抑制L型钙电流，抑制常数（K(B)）分别为11、246和512 nM，而1,4-二氢-2,6-二甲基-5-硝基-4-(2-[三氟甲基]苯基)-3-吡啶羧酸甲酯（Bay K8644）以33 nM的激活常数（K(A)）激活I(Ca)。300 nM Bay K8644对I(Ca)的最大激活显著降低了非洛地平的抑制效力（表观K(B)为165 nM），显著降低了维拉帕米的抑制效力（表观K(B)为737 nM），但显著增加了地尔硫䓬的抑制效力（表观K(B)为310 nM）。根据一种新的伪平衡双药结合模型，发现二氢吡啶激动剂Bay K8644与拮抗剂非洛地平之间的相互作用是纯粹竞争性的。发现Bay K8644与维拉帕米或地尔硫䓬之间的相互作用是非竞争性的，并且仅通过纳入维拉帕米的负相互作用因子ν = -0.60和地尔硫䓬的正相互作用因子ν = +0.24来描述。这些结果表明，在生理膜电位下，L型钙通道不能同时被二氢吡啶激动剂和拮抗剂占据，而它可以同时结合二氢吡啶激动剂和非二氢吡啶拮抗剂。一般来说，这些药物对L型钙通道的作用支持了一个通道结构域的概念，该结构域负责钙通道拮抗剂和激动剂的结合，其会随着膜电压和单个结合位点的占据情况而动态变化。
