Busch A E, Wagner C A, Schuster A, Waldegger S, Biber J, Murer H, Lang F
Institute of Physiology I, Eberhard-Karls-Universität Tübingen, Germany.
J Am Soc Nephrol. 1995 Dec;6(6):1547-51. doi: 10.1681/ASN.V661547.
Inorganic phosphate (Pi) induced an inward current (IP) in Xenopus oocytes expressing the human renal Na+/Pi cotransporter NaPi-3. At 100mM Na+, Pi-transport was independent of the holding potential and resulted in an apparent Km of 0.08 mM; lowering the Na+ concentration to 50 mM resulted in an increase of the apparent Km to 0.22 mM at -50 mV and to 0.31 mM at -90 mV. In contrast, the apparent Km for Na+ was not significantly influenced by the holding potential. A decrease of the pH from 7.8 to 6.8 resulted in a decrease of IP at 50 mM Na+, but not at 150 mM Na+. Arsenate induced inward currents through NaPi-3 and decreased the apparent Km in measurements of IP. Phosphonoformic acid itself induced no currents, but inhibited Pi-induced currents with an apparent Ki of 3.6 mM. In summary, NaPi-3 displays characteristic Na+/Pi cotransporter properties with relevant interactions with arsenate (transport substrate) and phosphonoformic acid (inhibitor). Monovalent and divalent Pi both appear to be transported by NaPi-3.
无机磷酸盐（Pi）在表达人肾Na⁺/Pi共转运体NaPi-3的非洲爪蟾卵母细胞中诱导了内向电流（IP）。在100 mM Na⁺时，Pi转运与钳制电位无关，表观Km为0.08 mM；将Na⁺浓度降至50 mM时，在-50 mV时表观Km增加至0.22 mM，在-90 mV时增加至0.31 mM。相反，Na⁺的表观Km不受钳制电位的显著影响。pH从7.8降至6.8导致在50 mM Na⁺时IP降低，但在150 mM Na⁺时未降低。砷酸盐通过NaPi-3诱导内向电流，并在IP测量中降低表观Km。膦甲酸本身不诱导电流，但以3.6 mM的表观Ki抑制Pi诱导的电流。总之，NaPi-3表现出特征性的Na⁺/Pi共转运体特性，与砷酸盐（转运底物）和膦甲酸（抑制剂）存在相关相互作用。单价和二价Pi似乎都由NaPi-3转运。
