McDonough A A, Zhang Y, Shin V, Frank J S
Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033, USA.
Am J Physiol. 1996 Apr;270(4 Pt 1):C1221-7. doi: 10.1152/ajpcell.1996.270.4.C1221.
The cardiac Na+ pump (Na+ -K+ -ATPase) provides the driving force for the Na+/Ca2+ exchanger, a determinant of intracellular Ca2+ stores. Three Na+ pump alpha-catalytic subunit isoforms are expressed in human heart, alpha1 and alpha2 are expressed in rat heart, and only alpha1 is expressed in guinea pig heart. The objective of this study was to determine whether there are isoform-specific patterns of expression in the transverse tubules (T tubules) vs. the peripheral sarcolemma. In adult rat cardiomyocytes, anti-alpha1-specific antibodies labeled the T tubules more intensely than the peripheral sarcolemma, in which labeling was patchy, the same pattern reported for distribution of the Na+/Ca2+ exchanger (J. S. Frank, G. Mottino, D. Reid, R. S. Molday, and K. D. Philipson, J. Cell Biol. 117: 337-345, 1992), whereas anti-alpha2- and anti-beta1-antibodies uniformly labeled T tubules and peripheral sarcolemma. In guinea pig cardiomyocytes, an anti-alpha-antibody against an extracellular epitope evenly labeled the peripheral sarcolemma and T tubules, and immunogold labeling demonstrated coincidence of alpha-subunits and intramembranous particles in sarcolemma. In summary, Na+ pumps are located in both peripheral sarcolemma and T tubules of cardiomyocytes expressing either multiple or single Na+ pump isoforms.
心脏钠泵（Na⁺-K⁺-ATP酶）为钠/钙交换体提供驱动力，而钠/钙交换体是细胞内钙储备的一个决定因素。人类心脏中表达三种钠泵α催化亚基异构体，大鼠心脏中表达α1和α2，豚鼠心脏中仅表达α1。本研究的目的是确定在横小管（T小管）与外周肌膜中是否存在异构体特异性表达模式。在成年大鼠心肌细胞中，抗α1特异性抗体标记T小管的强度高于外周肌膜，外周肌膜的标记呈斑块状，这与钠/钙交换体分布的报道模式相同（J.S.弗兰克、G.莫蒂诺、D.里德、R.S.莫尔代和K.D.菲利普森，《细胞生物学杂志》117:337 - 345，1992），而抗α2和抗β1抗体均匀地标记T小管和外周肌膜。在豚鼠心肌细胞中，针对细胞外表位的抗α抗体均匀地标记外周肌膜和T小管，免疫金标记显示α亚基与肌膜中的膜内颗粒重合。总之，钠泵位于表达多种或单一钠泵异构体的心肌细胞的外周肌膜和T小管中。
