Panet R, Digregorio D M, Brown R H
J Cell Physiol. 1987 Jul;132(1):57-64. doi: 10.1002/jcp.1041320108.
Potassium and sodium fluxes believed to be important in the cellular response to serum and growth factors have not been widely investigated in cells which have undergone terminal differentiation. In this study we have analyzed two main K+ transport systems--the ouabain-sensitive Na+/K+ pump and the bumetanide-sensitive transporter--in human muscle in vitro at two developmental stages: proliferating myoblasts and differentiated myotubes. Myoblast differentiation to myotubes was accompanied by a marked decrease in both the ouabain-sensitive and the bumetanide-sensitive K+ (Rb+) influxes. The addition of serum to the terminally differentiated myotubes had no effect on these K+ transporters. However, serum addition to serum-deprived, undifferentiated myoblasts produced a marked stimulation of these K+ fluxes. The bumetanide-sensitive K+ transporter in human myoblasts and myotubes has the following properties: (1) It carries 30% and 40% of the total K+ influx in myoblasts and myotubes, respectively. (2) It performs net efflux of K+ in the undifferentiated myoblasts and zero net flux (self-exchange) in terminally differentiated myotubes. (3) It is dependent on extracellular Na+ and Cl- in addition to K+. (4) In myoblasts, the Km value for K+ is 1.36 mM, similar to the Km for K+ of the Na+/K+ pump. (5) It is resistant to ouabain (up to 2 mM) and sensitive to furosemide (K0.5 = 5 X 10(-6) M) and bumetanide (K0.5 = 10(-7) M). These data indicate that following terminal differentiation of proliferating myoblasts to mitotically inactive myotubes there is an irreversible reduction of K+ fluxes with a change in the net flux of K+ carried by the bumetanide-sensitive transporter.
钾离子和钠离子通量被认为在细胞对血清和生长因子的反应中很重要，但在经历终末分化的细胞中尚未得到广泛研究。在本研究中，我们在体外分析了人类肌肉在两个发育阶段（增殖的成肌细胞和分化的肌管）中的两种主要钾离子转运系统——哇巴因敏感的钠钾泵和布美他尼敏感的转运体。成肌细胞向肌管的分化伴随着哇巴因敏感和布美他尼敏感的钾离子（铷离子）内流显著减少。向终末分化的肌管中添加血清对这些钾离子转运体没有影响。然而，向血清剥夺的未分化成肌细胞中添加血清会显著刺激这些钾离子通量。人类成肌细胞和肌管中的布美他尼敏感钾离子转运体具有以下特性：（1）它分别承担成肌细胞和肌管中总钾离子内流的30%和40%。（2）它在未分化的成肌细胞中进行钾离子的净外流，而在终末分化的肌管中净通量为零（自我交换）。（3）除了钾离子外，它还依赖细胞外的钠离子和氯离子。（4）在成肌细胞中，钾离子的米氏常数为1.36 mM，与钠钾泵的钾离子米氏常数相似。（5）它对哇巴因有抗性（高达2 mM），对呋塞米（半数抑制浓度=5×10⁻⁶ M）和布美他尼（半数抑制浓度=10⁻⁷ M）敏感。这些数据表明，增殖的成肌细胞终末分化为有丝分裂不活跃的肌管后，钾离子通量会发生不可逆的减少，且布美他尼敏感转运体所携带的钾离子净通量也会发生变化。
