Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark.
J Membr Biol. 2010 Mar;234(1):35-45. doi: 10.1007/s00232-010-9237-6. Epub 2010 Feb 23.
Previous studies in expression systems have found different ion activation of the Na(+)/K(+)-ATPase isozymes, which suggest that different muscles have different ion affinities. The rate of ATP hydrolysis was used to quantify Na(+),K(+)-ATPase activity, and the Na(+) affinity of Na(+),K(+)-ATPase was studied in total membranes from rat muscle and purified membranes from muscle with different fiber types. The Na(+) affinity was higher (K(m) lower) in oxidative muscle compared with glycolytic muscle and in purified membranes from oxidative muscle compared with glycolytic muscle. Na(+),K(+)-ATPase isoform analysis implied that heterodimers containing the beta(1) isoform have a higher Na(+) affinity than heterodimers containing the beta(2) isoform. Immunoprecipitation experiments demonstrated that dimers with alpha(1) are responsible for approximately 36% of the total Na,K-ATPase activity. Selective inhibition of the alpha(2) isoform with ouabain suggested that heterodimers containing the alpha(1) isoform have a higher Na(+) affinity than heterodimers containing the alpha(2) isoform. The estimated K(m) values for Na(+) are 4.0, 5.5, 7.5 and 13 mM for alpha(1)beta(1), alpha(2)beta(1), alpha(1)beta(2) and alpha(2)beta(2), respectively. The affinity differences and isoform distributions imply that the degree of activation of Na(+),K(+)-ATPase at physiological Na(+) concentrations differs between muscles (oxidative and glycolytic) and between subcellular membrane domains with different isoform compositions. These differences may have consequences for ion balance across the muscle membrane.
先前在表达系统中的研究发现，不同的离子对 Na(+)/K(+)-ATPase 同工酶的激活作用不同，这表明不同的肌肉具有不同的离子亲和力。通过水解 ATP 的速率来定量 Na(+),K(+)-ATPase 活性，并研究来自大鼠肌肉的总膜和来自具有不同纤维类型的肌肉的纯化膜中的 Na(+),K(+)-ATPase 的 Na(+)亲和力。与糖酵解肌肉相比，氧化肌肉中的 Na(+)亲和力更高（Km 值更低），并且与糖酵解肌肉中的纯化膜相比，氧化肌肉中的 Na(+),K(+)-ATPase 亲和力更高。Na(+),K(+)-ATPase 同工型分析表明，含有β(1)同工型的异二聚体比含有β(2)同工型的异二聚体具有更高的 Na(+)亲和力。免疫沉淀实验表明，具有α(1)的二聚体负责约 36%的总 Na,K-ATPase 活性。用哇巴因选择性抑制α(2)同工型表明，含有α(1)同工型的异二聚体比含有α(2)同工型的异二聚体具有更高的 Na(+)亲和力。估计的 Na(+)Km 值分别为 4.0、5.5、7.5 和 13 mM，对于α(1)β(1)、α(2)β(1)、α(1)β(2)和α(2)β(2)。亲和力差异和同工型分布表明，Na(+),K(+)-ATPase 在生理 Na(+)浓度下的激活程度在肌肉（氧化和糖酵解）之间以及具有不同同工型组成的亚细胞膜域之间不同。这些差异可能对肌肉膜两侧的离子平衡产生影响。
