Kristensen J M, Kristensen M, Juel C
Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, Denmark.
Acta Physiol Scand. 2004 Sep;182(1):69-76. doi: 10.1111/j.1365-201X.2004.01297.x.
Sodium/bicarbonate co-transport (NBC) has been suggested to have a role in muscle pH regulation. We investigated the presence of NBC proteins in rat and human muscle samples and the fibre type distribution of the identified NBCs.
Western blotting of muscle homogenates and sarcolemmal membranes (sarcolemmal giant vesicles) were used to screen for the presence of NBCs. Immunohistochemistry was used for the subcellular localization. The functional test revealed that approximately half of the pH recovery in sarcolemmal vesicles produced from rat muscle is mediated by bicarbonate-dependent transport. This indicates that the NBCs are preserved in the vesicles. The western blotting experiments demonstrated the existence of at least two NBC proteins in skeletal muscle. One NBC protein (approximately 150 kDa) seems to be related to the kidney/pancreas/heart isoform NBC1, whereas the other protein (approximately 200 kDa) is related to the NBC4 isoform. The two NBC proteins represent the electrogenic isoforms named NBCe1 and NBCe2. Membrane fractionation and immunofluorescence techniques confirmed that the two NBCs are located in the sarcolemmal membrane as well as in some internal membranes, probably the T-tubules. The two NBCs localized in muscle have distinct fibre type distributions.
Skeletal muscle possesses two variants of the sodium/bicarbonate co-transporter (NBC) isoforms, which have been called NBCe1 and NBCe2.
钠/碳酸氢根共转运体（NBC）被认为在肌肉pH调节中发挥作用。我们研究了大鼠和人类肌肉样本中NBC蛋白的存在情况以及所鉴定出的NBCs的纤维类型分布。
使用肌肉匀浆和肌膜（肌膜巨型囊泡）的蛋白质免疫印迹法来筛选NBCs的存在。免疫组织化学用于亚细胞定位。功能测试表明，大鼠肌肉产生的肌膜囊泡中约一半的pH恢复是由碳酸氢根依赖性转运介导的。这表明NBCs保留在囊泡中。蛋白质免疫印迹实验证明骨骼肌中存在至少两种NBC蛋白。一种NBC蛋白（约150 kDa）似乎与肾/胰腺/心脏异构体NBC1相关，而另一种蛋白（约200 kDa）与NBC4异构体相关。这两种NBC蛋白代表了名为NBCe1和NBCe2的电生性异构体。膜分级分离和免疫荧光技术证实这两种NBCs位于肌膜以及一些内膜中，可能是横小管。在肌肉中定位的这两种NBCs具有不同的纤维类型分布。
骨骼肌拥有钠/碳酸氢根共转运体（NBC）异构体的两种变体，分别被称为NBCe1和NBCe2。
