Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, 12700 East 19th Avenue, P15-8006, B-139, Aurora, CO 80045, USA; Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, Venustiano Carranza #2405, San Luis Potosí, SLP 78210, México.
Biochem Biophys Res Commun. 2013 Sep 20;439(2):270-4. doi: 10.1016/j.bbrc.2013.08.044. Epub 2013 Aug 20.
Ca(2+) influx via L-type voltage-gated Ca(2+) channels supports the plateau phase of ventricular action potentials and is the trigger for excitation-contraction (EC) coupling in the myocardium. Rad, a member of the RGK (Rem, Rem2, Rad, Gem/Kir) family of monomeric G proteins, regulates ventricular action potential duration and EC coupling gain through its ability to inhibit cardiac L-type channel activity. In this study, we have investigated the potential dysfunction of a naturally occurring Rad variant (Q66P) that has been associated with congestive heart failure in humans. Specifically, we have tested whether Rad Q66P limits, or even eliminates, the inhibitory actions of Rad on CaV1.2 and CaV1.3, the two L-type channel isoforms known to be expressed in the heart. We have found that mouse Rad Q65P (the murine equivalent of human Rad Q66P) inhibits L-type currents conducted by CaV1.2 or CaV1.3 channels as potently as wild-type Rad (>95% inhibition of both channels). In addition, Rad Q65P attenuates the gating movement of both channels as effectively as wild-type Rad, indicating that the Q65P substitution does not differentially impair any of the three described modes of L-type channel inhibition by RGK proteins. Thus, we conclude that if Rad Q66P contributes to cardiomyopathy, it does so via a mechanism that is not related to its ability to inhibit L-type channel-dependent processes per se. However, our results do not rule out the possibility that decreased expression, mistargeting or altered regulation of Rad Q66P may reduce the RGK protein's efficacy in vivo.
钙离子经 L 型电压门控钙离子通道内流可支持心室动作电位平台期，并触发心肌兴奋-收缩偶联（EC 耦联）。Rad 是单体 G 蛋白 RGK（Rem、Rem2、Rad、Gem/Kir）家族的成员，通过抑制心脏 L 型通道活性，调节心室动作电位时程和 EC 耦联增益。在这项研究中，我们研究了一种与人类充血性心力衰竭相关的自然发生的 Rad 变体（Q66P）是否存在功能障碍。具体而言，我们测试了 Rad Q66P 是否限制甚至消除了 Rad 对 CaV1.2 和 CaV1.3 的抑制作用，CaV1.2 和 CaV1.3 是已知在心脏中表达的两种 L 型通道同工型。我们发现，鼠 Rad Q65P（与人 Rad Q66P 对应的鼠 Rad 变体）与野生型 Rad 一样有效地抑制 CaV1.2 或 CaV1.3 通道介导的 L 型电流（两种通道的抑制率均>95%）。此外，Rad Q65P 与野生型 Rad 一样有效地减弱两种通道的门控运动，表明 Q65P 取代不会使 RGK 蛋白对 L 型通道抑制的三种描述模式中的任何一种产生差异。因此，我们得出结论，如果 Rad Q66P 导致心肌病，那么这种作用不是通过其本身抑制 L 型通道依赖性过程的能力实现的。然而，我们的结果并不能排除 Rad Q66P 表达减少、靶向错误或调节改变可能降低 RGK 蛋白在体内的效力。
