Bussolati O, Laris P C, Longo N, Dall'Asta V, Franchi-Gazzola R, Guidotti G G, Gazzola G C
Biochim Biophys Acta. 1986 Jan 29;854(2):240-50. doi: 10.1016/0005-2736(86)90116-1.
The distribution ratio of the lipophilic cation tetraphenylphosphonium (TPP+) has been used to estimate the electrical potential difference across the plasma membrane in cultured human fibroblasts. These cells exhibit a membrane potential markedly influenced by the diffusion potential of K+. High extracellular potassium concentrations depolarize human fibroblasts and depress the activity of transport systems A, ASC (both serving for zwitterionic amino acids), X-AG (for anionic amino acids), and y+ (for cationic amino acids). High doses (100 microM) of the K+-ionophore valinomycin hyperpolarize the cells. This condition enhances the activity of systems A, ASC and y+. Transport systems L (for neutral amino acids) and x-C (for anionic amino acids) are insensitive to changes in extracellular K+ or to valinomycin. System X-AG is inhibited by the addition of 100 microM valinomycin, but the effect of the ionophore appears to be potential-independent. These results indicate that: (a) the activity of systems L and x-C is potential-independent and (b) the activity of systems A, ASC, X-AG and y+ is sensitive to alterations of external [K+] associated to changes in membrane potential.
亲脂性阳离子四苯基鏻（TPP +）的分配比已被用于估算培养的人成纤维细胞质膜两侧的电势差。这些细胞表现出的膜电位受到K +扩散电位的显著影响。高细胞外钾浓度会使人类成纤维细胞去极化，并抑制转运系统A、ASC（两者都用于两性离子氨基酸）、X-AG（用于阴离子氨基酸）和y +（用于阳离子氨基酸）的活性。高剂量（100 microM）的K +离子载体缬氨霉素会使细胞超极化。这种情况会增强系统A、ASC和y +的活性。转运系统L（用于中性氨基酸）和x-C（用于阴离子氨基酸）对细胞外K +的变化或缬氨霉素不敏感。添加100 microM缬氨霉素会抑制系统X-AG，但离子载体的作用似乎与电位无关。这些结果表明：（a）系统L和x-C的活性与电位无关；（b）系统A、ASC、X-AG和y +的活性对与膜电位变化相关的外部[K +]改变敏感。
