Maan A C, Hosey M M
Circ Res. 1987 Sep;61(3):379-88. doi: 10.1161/01.res.61.3.379.
The interaction of 1,4-dihydropyridine derivatives with their receptors on voltage-dependent calcium channels in cardiac membranes was studied to determine if there are basic differences in the binding properties of ligands that cause inhibition or activation of calcium channels. The binding characteristics of 6 pure stereoisomers, (-) and (+)202-791, (-) and (+)Bay k 8644, (-) and (+)PN 200-110, as well as racemic Bay k 8644 and nitrendipine, were compared. Competition studies using the cold ligands and 3 different radiolabelled dihydropyridines, (+)[3H]PN 200-110, (+/-)[3H]nitrendipine, and (+/-)[3H]Bay k 8644, showed that, for each combination tested, the labelled dihydropyridine could be displaced by the cold dihydropyridine. The binding reactions were markedly affected by temperature. The Kd values for most compounds were significantly higher (5-19 times) at 0 degrees than at 37 degrees C. In contrast, the affinity of (+)PN 200-110 was similar at 0 degrees and 37 degrees C, but slightly higher at 25 degrees C. A thermodynamic analysis indicated that the binding of the two pure isomers that are Ca2+-channel activators ("agonists"), (-)Bay k 8644 and (+)202-791, was driven entirely by enthalpy and was associated with an unfavorable decrease in entropy. This was in marked contrast to the binding of the inhibitors ("antagonists"). The binding of (+)PN 200-110 and nitrendipine at low temperatures was driven largely or entirely by entropy. Other antagonist-binding reactions were driven mainly by enthalpy but were associated with favorable increases in entropy. The affinity of the three radiolabelled ligands for the dihydropyridine receptor differed 100 times and appeared to be due to large differences in dissociation rate constants for each of the ligands. The rates of dissociation of (+)[3H]PN 200-110 and (+/-)[3H]nitrendipine, but not of (+/-)[3H]Bay k 8644, were significantly slowed by diltiazem, a calcium-channel inhibitor that binds to another receptor on the calcium channel. The results show that there were marked differences in the binding of the various dihydropyridines and suggest that the energetics of binding of Ca2+-channel activators and inhibitors may be fundamentally different.
研究了1,4 - 二氢吡啶衍生物与心肌膜电压依赖性钙通道上的受体之间的相互作用，以确定引起钙通道抑制或激活的配体在结合特性上是否存在基本差异。比较了6种纯立体异构体（(-)和(+)202 - 791、(-)和(+)Bay k 8644、(-)和(+)PN 200 - 110）以及外消旋Bay k 8644和尼群地平的结合特性。使用冷配体和3种不同的放射性标记二氢吡啶（(+)[³H]PN 200 - 110、(+/-)[³H]尼群地平、(+/-)[³H]Bay k 8644）进行的竞争研究表明，对于所测试的每种组合，标记的二氢吡啶均可被冷二氢吡啶取代。结合反应受温度的显著影响。大多数化合物在0℃时的Kd值比在37℃时显著更高（5 - 19倍）。相比之下，(+)PN 200 - 110在0℃和37℃时的亲和力相似，但在25℃时略高。热力学分析表明，两种作为Ca²⁺通道激活剂（“激动剂”）的纯异构体(-)Bay k 8644和(+)202 - 791的结合完全由焓驱动，并且伴随着不利的熵减少。这与抑制剂（“拮抗剂”）的结合形成了显著对比。(+)PN 200 - 110和尼群地平在低温下的结合主要或完全由熵驱动。其他拮抗剂结合反应主要由焓驱动，但伴随着有利的熵增加。三种放射性标记配体对二氢吡啶受体的亲和力相差100倍，这似乎是由于每种配体解离速率常数的巨大差异所致。钙通道抑制剂地尔硫䓬与钙通道上的另一个受体结合，它显著减慢了(+)[³H]PN 200 - 110和(+/-)[³H]尼群地平的解离速率，但未减慢(+/-)[³H]Bay k 8644的解离速率。结果表明，各种二氢吡啶的结合存在显著差异，这表明Ca²⁺通道激活剂和抑制剂结合的能量学可能存在根本不同。
