速尿敏感的人红细胞钾（铷）转运：运转模式、对细胞外和细胞内钠离子的依赖性、动力学、pH依赖性以及细胞体积和N-乙基马来酰亚胺的影响
Furosemide-sensitive K+ (Rb+) transport in human erythrocytes: modes of operation, dependence on extracellular and intracellular Na+, kinetics, pH dependency and the effect of cell volume and N-ethylmaleimide.
作者信息
Duhm J
机构信息
Physiologisches Institut, Universität München, Germany.
出版信息
J Membr Biol. 1987;98(1):15-32. doi: 10.1007/BF01871042.
The effect of extracellular and intracellular Na+ (Nao+, Nai+) on ouabain-resistant, furosemide-sensitive (FS) Rb+ transport was studied in human erythrocytes under varying experimental conditions. The results obtained are consistent with the view that a (1 Na+ + 1 K+ + 2 Cl-) cotransport system operates in two different modes: mode i) promoting bidirectional 1:1 (Na+-K+) cotransport, and mode ii) a Nao+-independent 1:1 ki+ exchange requiring Nai+ which, however, is not extruded. The activities of the two modes of operation vary strictly in parallel to each other among erythrocytes of different donors and in cell fractions of individual donors separated according to density. Rb+ uptake through Rbo+/Ki+ exchange contributes about 25% to total Rb+ uptake in 145 mM NaCl media containing 5 mM RbCl at normal Nai+ (pH 7.4). Na+-K+ cotransport into the cells occurs largely additive to K+/K+ exchange. Inward Na+-Rb+ cotransport exhibits a substrate inhibition at high Rbo+. With increasing pH, the maximum rate of cotransport is accelerated at the expense of K+/K+ exchange (apparent pK close to pH 7.4). The apparent KmRbo+ of Na+-K+ cotransport is low (2 mM) and almost independent of pH, and high for K+/K+ exchange (10 to 15 mM), the affinity increasing with pH. The two modes are discussed in terms of a partial reaction scheme of (1 Na+ + 1 K+ + 2 Cl-) cotransport with ordered binding and debinding, exhibiting a glide symmetry (first on outside = first off inside) as proposed by McManus for duck erythrocytes (McManus, T.J., 1987, Fed. Proc., in press). N-ethylmaleimide (NEM) chemically induces a Cl--dependent K+ transport pathway that is independent of both Nao+ and Nai+. This pathway differs in many properties from the basal, Nao+-independent K+/K+ exchange active in untreated human erythrocytes at normal cell volume. Cell swelling accelerates a Nao+-independent FS K+ transport pathway which most probably is not identical to basal K+/K+ exchange. Ko+ less than Nao+ less than Lio+ less than Mgo2+ reduce furosemide-resistant Rb+ inward leakage relative to cholineo+.
在不同实验条件下，研究了细胞外和细胞内的Na⁺（Nao⁺、Nai⁺）对人红细胞中哇巴因耐药、呋塞米敏感（FS）的Rb⁺转运的影响。所得结果与以下观点一致：即（1个Na⁺ + 1个K⁺ + 2个Cl⁻）共转运系统以两种不同模式运行：模式i）促进双向1:1（Na⁺-K⁺）共转运，模式ii）一种不依赖Nao⁺的1:1 K⁺交换，需要Nai⁺，但Nai⁺不会被排出。在不同供体的红细胞以及根据密度分离的单个供体细胞组分中，两种运行模式的活性严格相互平行变化。在正常Nai⁺（pH 7.4）、含有5 mM RbCl的145 mM NaCl培养基中，通过Rbo⁺/K⁺交换的Rb⁺摄取约占总Rb⁺摄取的25%。Na⁺-K⁺共转运进入细胞在很大程度上是与K⁺/K⁺交换相加的。内向Na⁺-Rb⁺共转运在高Rbo⁺时表现出底物抑制。随着pH升高，共转运的最大速率加快，代价是K⁺/K⁺交换（表观pK接近pH 7.4）。Na⁺-K⁺共转运的表观KmRbo⁺较低（2 mM）且几乎与pH无关，而K⁺/K⁺交换的表观KmRbo⁺较高（10至15 mM），亲和力随pH升高而增加。根据（1个Na⁺ + 1个K⁺ + 2个Cl⁻）共转运的部分反应方案讨论了这两种模式，该方案具有有序的结合和解离，表现出如McManus对鸭红细胞所提出的滑移对称性（先在外侧 = 先在内侧解离）（McManus, T.J., 1987, Fed. Proc., 即将发表）。N-乙基马来酰亚胺（NEM）化学诱导一种依赖Cl⁻的K⁺转运途径，该途径独立于Nao⁺和Nai⁺。该途径在许多特性上不同于正常细胞体积下未处理的人红细胞中活跃的基础的、不依赖Nao⁺的K⁺/K⁺交换。细胞肿胀加速一种不依赖Nao⁺的FS K⁺转运途径，该途径很可能与基础的K⁺/K⁺交换不同。相对于cholineo⁺，Ko⁺ < Nao⁺ < Lio⁺ < Mgo²⁺降低了呋塞米耐药的Rb⁺内向泄漏。
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