Departamento de Bioquímica (J.A.M.D.L.R., M.G.-C., G.Á.) and Departamento de Química (T.M.-P.), Cinvestav-IPN, Mexico City, Mexico and Instituto de Biotecnología (T.N.) and Instituto de Fisiología Celular (J.C.G.), Universidad Nacional Autónoma de México, Cuernavaca, Mexico.
Departamento de Bioquímica (J.A.M.D.L.R., M.G.-C., G.Á.) and Departamento de Química (T.M.-P.), Cinvestav-IPN, Mexico City, Mexico and Instituto de Biotecnología (T.N.) and Instituto de Fisiología Celular (J.C.G.), Universidad Nacional Autónoma de México, Cuernavaca, Mexico
Mol Pharmacol. 2020 Sep;98(3):211-221. doi: 10.1124/mol.120.119982. Epub 2020 Jun 25.
Amino acid-derived isoindolines are synthetic compounds that were created with the idea of investigating their biological actions. The amino acid moiety was included on the grounds that it may help to avoid toxic effects. Recently, the isoindoline MDIMP was shown to inhibit both cardiac excitation-contraction coupling and voltage-dependent calcium channels. Here, we revealed that MDIMP binds preferentially to low-voltage-activated (LVA) channels. Using a holding potential of -90 mV, the following IC values were found (in micromolars): >1000 (Ca2.3), 957 (Ca1.3), 656 (Ca1.2), 219 (Ca3.2), and 132 (Ca3.1). Moreover, the isoindoline also promoted both accelerated inactivation kinetics of high-voltage-activated Ca channels and a modest upregulation of Ca1.3 and Ca2.3. Additional data indicate that although MDIMP binds to the closed state of the channels, it has more preference for the inactivated one. Concerning Ca3.1, the compound did not alter the shape of the instantaneous current-voltage curve, and substituting one or two residues in the selectivity filter drastically increased the IC value, suggesting that MDIMP binds to the extracellular side of the pore. However, an outward current failed in removing the inhibition, which implies an alternative mechanism may be involved. The enantiomer ()-MDIMP [methyl ()-2-(1,3-dihydroisoindol-2-yl)-4-methylpentanoate], on the other hand, was synthesized and evaluated, but it did not improve the affinity to LVA channels. Implications of these findings are discussed in terms of the possible underlying mechanisms and pharmacological relevance. SIGNIFICANCE STATEMENT: We have studied the regulation of voltage-gated calcium channels by MDIMP, which disrupts excitation-contraction coupling in cardiac myocytes. The latter effect is more potent in atrial than ventricular myocytes, and this could be explained by our results showing that MDIMP preferentially blocks low-voltage-activated channels. Our data also provide mechanistic insights about the blockade and suggest that MDIMP is a promising member of the family of Ca channel blockers, with possible application to the inhibition of subthreshold membrane depolarizations.
氨基酸衍生的异吲哚啉是合成化合物，其被合成的初衷是为了研究它们的生物学作用。引入氨基酸部分是因为它可能有助于避免毒性作用。最近，异吲哚啉 MDIMP 被证明可以抑制心脏兴奋-收缩偶联和电压依赖性钙通道。在这里，我们揭示了 MDIMP 优先与低电压激活（LVA）通道结合。在保持电位为-90 mV 的情况下，发现以下 IC 值（以微摩尔计）：>1000（Ca2.3）、957（Ca1.3）、656（Ca1.2）、219（Ca3.2）和 132（Ca3.1）。此外，该异吲哚啉还促进了高电压激活钙通道的加速失活动力学和 Ca1.3 和 Ca2.3 的适度上调。其他数据表明，尽管 MDIMP 与通道的关闭状态结合，但它对失活状态更有偏好。关于 Ca3.1，该化合物不会改变瞬时电流-电压曲线的形状，并且在选择性过滤器中替换一个或两个残基会大大增加 IC 值，这表明 MDIMP 与通道的细胞外侧结合。然而，外向电流未能消除抑制作用，这表明可能涉及替代机制。另一方面，对映异构体（）-MDIMP [甲基（）-2-（1,3-二氢异吲哚-2-基）-4-甲基戊酸酯]被合成并进行了评估，但它并没有提高对 LVA 通道的亲和力。根据可能的潜在机制和药理学相关性，讨论了这些发现的意义。我们研究了 MDIMP 对电压门控钙通道的调节作用，该调节作用破坏了心肌细胞的兴奋-收缩偶联。后一种作用在心房肌细胞中比心室肌细胞更强，这可以用我们的结果来解释，表明 MDIMP 优先阻断低电压激活通道。我们的数据还提供了关于阻断的机制见解，并表明 MDIMP 是钙通道阻滞剂家族中很有前途的一员，可能适用于抑制亚阈值膜去极化。
