Zimmer T, Biskup C, Bollensdorff C, Benndorf K
Institute of Physiology II, Friedrich Schiller University Jena, Teichgraben 8, 07740 Jena, Germany.
J Membr Biol. 2002 Mar 1;186(1):13-21. doi: 10.1007/s00232-001-0131-0.
Voltage-dependent Na+ channels are heteromultimers consisting of a pore-forming a subunit and accessory b subunits. In order to provide more insight into the trafficking and assembly of the cardiac Na+ channel complex, we investigated the subcellular localization of the Na+ channel beta1 and beta2 subunits, both in the absence and presence of the human heart Na+ channel (hH1). We fused spectrally distinct variants of the green fluorescent protein (GFP) to hH1 and to the beta1 and beta2 subunit, and expressed the optically labeled b subunits separately or in combination with hH1 in HEK293 cells. In contrast to the predominant localization of hH1 channels within the endoplasmic reticulum (ER), both beta subunits were clearly targeted to the plasma membrane when expressing their cDNAs alone. Upon coexpression of the a subunit, the beta1 subunit was efficiently retained within the ER and found to be colocalized with hH1. In contrast to this, hH1 and the beta2 subunit were not colocalized, i.e., they were detected mainly within the ER and the plasma membrane, respectively. These results indicate that hH1 and the b2 subunit are transported separately to the plasma membrane whereas the hH1/beta1 complex occurs already within the ER, which possibly facilitates trafficking of the channel complex to the plasma membrane.
电压依赖性钠通道是由一个形成孔道的α亚基和辅助性β亚基组成的异源多聚体。为了更深入了解心脏钠通道复合物的运输和组装过程，我们研究了在不存在和存在人心脏钠通道（hH1）的情况下，钠通道β1和β2亚基的亚细胞定位。我们将绿色荧光蛋白（GFP）的光谱不同变体分别与hH1以及β1和β2亚基融合，并在HEK293细胞中单独表达或与hH1共同表达经光学标记的β亚基。与hH1通道主要定位于内质网（ER）不同，单独表达其cDNA时，两个β亚基均明确靶向质膜。在α亚基共表达时，β1亚基有效地保留在内质网中，并发现与hH1共定位。与此相反，hH1和β2亚基没有共定位，即它们分别主要在内质网和质膜中被检测到。这些结果表明，hH1和β2亚基分别被运输到质膜，而hH1/β1复合物在内质网中就已形成，这可能有助于通道复合物向质膜的运输。
