Department of Physiology, University of Kentucky College of Medicine, Lexington, USA.
Channels (Austin). 2012 May-Jun;6(3):166-73. doi: 10.4161/chan.20192.
The L-type calcium channels (LTCC) are critical for maintaining Ca(2+)-homeostasis. In heterologous expression studies, the RGK-class of Ras-related G-proteins regulates LTCC function; however, the physiological relevance of RGK-LTCC interactions is untested.
In this report we test the hypothesis that the RGK protein, Rem, modulates native Ca(2+) current (I(Ca,L)) via LTCC in murine cardiomyocytes.
Rem knockout mice (Rem(-/-)) were engineered, and I(Ca,L) and Ca(2+) -handling properties were assessed. Rem(-/-) ventricular cardiomyocytes displayed increased I(Ca,L) density. I(Ca,L) activation was shifted positive on the voltage axis, and β-adrenergic stimulation normalized this shift compared with wild-type I(Ca,L). Current kinetics, steady-state inactivation, and facilitation was unaffected by Rem(-/-) . Cell shortening was not significantly different. Increased I(Ca,L) density in the absence of frank phenotypic differences motivated us to explore putative compensatory mechanisms. Despite the larger I(Ca,L) density, Rem(-/-) cardiomyocyte Ca(2+) twitch transient amplitude was significantly less than that compared with wild type. Computer simulations and immunoblot analysis suggests that relative dephosphorylation of Rem(-/-) LTCC can account for the paradoxical decrease of Ca(2+) transients.
This is the first demonstration that loss of an RGK protein influences I(Ca,L) in vivo in cardiac myocytes.
L 型钙通道（LTCC）对于维持钙稳态至关重要。在异源表达研究中，Ras 相关 G 蛋白的 RGK 类调节 LTCC 功能；然而，RGK-LTCC 相互作用的生理相关性尚未得到测试。
本报告测试了以下假设，即 RGK 蛋白 Rem 通过 LTCC 调节心肌细胞中的内源性 Ca(2+)电流（I(Ca,L)）。
构建了 Rem 敲除小鼠（Rem(-/-)），并评估了 I(Ca,L)和 Ca(2+)处理特性。Rem(-/-)心室肌细胞显示出增加的 I(Ca,L)密度。I(Ca,L)的激活在电压轴上向正方向转移，与野生型 I(Ca,L)相比，β-肾上腺素刺激使这种转移正常化。电流动力学、稳态失活和易化不受 Rem(-/-)的影响。细胞缩短没有显著差异。在没有明显表型差异的情况下增加 I(Ca,L)密度，促使我们探索潜在的代偿机制。尽管 I(Ca,L)密度较大，但 Rem(-/-)心肌细胞的 Ca(2+)抽搐瞬态幅度明显小于野生型。计算机模拟和免疫印迹分析表明，Rem(-/-)LTCC 的相对去磷酸化可以解释 Ca(2+)瞬变的矛盾减少。
这是首次证明 RGK 蛋白缺失会影响心脏肌细胞中体内的 I(Ca,L)。
