Boron W F, Boulpaep E L
J Gen Physiol. 1983 Jan;81(1):53-94. doi: 10.1085/jgp.81.1.53.
We have used pH-, Na-, and Cl-sensitive microelectrodes to study basolateral HCO3- transport in isolated, perfused proximal tubules of the tiger salamander Ambystoma tigrinum. In one series of experiments, we lowered basolateral pH (pHb) from 7.5 to 6.8 by reducing [HCO3-]b from 10 to 2 mM at a constant pCO2. This reduction of pHb and [HCO3-]b causes a large (approximately 0.35), rapid fall in pHi as well as a transient depolarization of the basolateral membrane. Returning pHb and [HCO3-]b to normal has the opposite effects. Similar reductions of luminal pH (pHl) and [HCO3-]l have only minor effects. The reduction of [HCO3-]b and pHb also produces a reversible fall in aiNa. In a second series of experiments, we reduced [Na+]b at constant [HCO3-]b and pHb, and also observed a rapid fall in pHi and a transient basolateral depolarization. These changes are reversed by returning [Na+]b to normal. The effects of altering [Na+]l in the presence of HCO3-, or of altering [Na+]b in the nominal absence of HCO3-, are substantially less. Although the effects on pHi and basolateral membrane potential of altering either [HCO3-]b or [Na+]b are largely blocked by 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonate (SITS), they are not affected by removal of Cl-, nor are there accompanying changes in aiCl consistent with a tight linkage between Cl- fluxes and those of Na+ and HCO3-. The aforementioned changes are apparently mediated by a single transport system, not involving Cl-. We conclude that HCO3- transport is restricted to the basolateral membrane, and that HCO3- fluxes are linked to those of Na+. The data are compatible with an electrogenic Na/HCO3 transporter that carries Na+, HCO3-, and net negative charge in the same direction.
我们使用了对pH、Na和Cl敏感的微电极，来研究虎螈（Ambystoma tigrinum）离体灌注近端小管基底外侧HCO₃⁻的转运。在一系列实验中，我们在恒定的pCO₂条件下，将基底外侧HCO₃⁻浓度（[HCO₃⁻]b）从10 mM降至2 mM，从而使基底外侧pH（pHb）从7.5降至6.8。pHb和[HCO₃⁻]b的这种降低导致细胞内pH（pHi）大幅（约0.35）快速下降，以及基底外侧膜的短暂去极化。将pHb和[HCO₃⁻]b恢复正常则产生相反的效果。管腔pH（pHl）和[HCO₃⁻]l的类似降低只有轻微影响。[HCO₃⁻]b和pHb的降低也会使细胞内Na（aiNa）产生可逆下降。在第二系列实验中，我们在恒定的[HCO₃⁻]b和pHb条件下降低[Na⁺]b，也观察到pHi快速下降和基底外侧短暂去极化。将[Na⁺]b恢复正常可逆转这些变化。在存在HCO₃⁻的情况下改变[Na⁺]l，或在名义上不存在HCO₃⁻的情况下改变[Na⁺]b，其影响要小得多。尽管改变[HCO₃⁻]b或[Na⁺]b对pHi和基底外侧膜电位的影响在很大程度上被4-乙酰氨基-4-异硫氰基芪-2,2'-二磺酸（SITS）阻断，但它们不受Cl⁻去除的影响，并且aiCl也没有伴随变化，这与Cl⁻通量与Na⁺和HCO₃⁻通量之间的紧密联系不一致。上述变化显然由单一转运系统介导，不涉及Cl⁻。我们得出结论，HCO₃⁻转运仅限于基底外侧膜，并且HCO₃⁻通量与Na⁺通量相关联。这些数据与一种电生Na⁺/HCO₃⁻转运体相符，该转运体在同一方向上转运Na⁺、HCO₃⁻和净负电荷。
