Lopes A G, Siebens A W, Giebisch G, Boron W F
Am J Physiol. 1987 Aug;253(2 Pt 2):F340-50. doi: 10.1152/ajprenal.1987.253.2.F340.
This study was undertaken to determine whether the proximal tubule of the mud puppy Necturus maculosus possesses a basolateral Na/HCO3 cotransporter. We examined the effects on basolateral membrane potential (Vbl) and intracellular pH (pHi) of 1) lowering basolateral [HCO3-] at constant PCO2, and 2) replacing Na+ with N-methyl-D-glucamine. Vbl and pHi were measured with Ling-Gerard and liquid-membrane pH microelectrodes, respectively, in isolated tubules perfused in vitro. We found that decreasing basolateral [HCO3-] from 10 mM (pH 7.5) to 2 mM (pH 6.8) resulted in an immediate depolarization of 14.9 mV, and a pHi decrease of 0.35. SITS (4-acetamido-4'-isothiocyanostibene-2,2'-disulfonic acid, 0.5 mM) inhibited the HCO3-induced depolarization by 87% and inhibited the initial rate of the pHi decrease by 79%. Replacement of basolateral Na+ with N-methyl-D-glucamine resulted in an immediate depolarization of 11.3 mV, and a pHi decrease of 0.36. SITS inhibited the zero Na-induced depolarization by 86% and the initial rate of the pHi decrease by 81%. Nominal removal of basolateral HCO3- (replaced with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) inhibited the zero Na-induced depolarization by 64%, whereas nominal removal of Na+ inhibited the 2 mM HCO3-induced depolarization by 67%. Replacement of all basolateral Cl- with glucuronate did not inhibit the changes in Vbl induced by changing [HCO3-] or [Na+]. Observations similar to those described above have been made previously on Ambystoma proximal tubules, and attributed to an electrogenic Na/HCO3 cotransport mechanism that carries HCO3-, Na+, and net negative charge in the same direction. We conclude that Necturus proximal tubules possess a similar, if not identical, electrogenic Na/HCO3 cotransport mechanism.
本研究旨在确定泥螈（Necturus maculosus）近端小管是否存在基底外侧钠/碳酸氢根共转运体。我们研究了以下两种情况对基底外侧膜电位（Vbl）和细胞内pH值（pHi）的影响：1）在恒定PCO₂条件下降低基底外侧[HCO₃⁻]浓度；2）用N-甲基-D-葡糖胺替代Na⁺。分别使用凌-杰勒德微电极和液膜pH微电极，在体外灌注的分离小管中测量Vbl和pHi。我们发现，将基底外侧[HCO₃⁻]从10 mM（pH 7.5）降至2 mM（pH 6.8）会导致立即去极化14.9 mV，pHi降低0.35。4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸（SITS，0.5 mM）可使HCO₃⁻诱导的去极化抑制87%，并使pHi降低的初始速率抑制79%。用N-甲基-D-葡糖胺替代基底外侧Na⁺会导致立即去极化11.3 mV，pHi降低0.36。SITS可使零钠诱导的去极化抑制86%，并使pHi降低的初始速率抑制81%。名义上去除基底外侧HCO₃⁻（用N-2-羟乙基哌嗪-N'-2-乙磺酸替代）可使零钠诱导的去极化抑制64%，而名义上去除Na⁺可使2 mM HCO₃⁻诱导的去极化抑制67%。用葡糖醛酸根替代所有基底外侧Cl⁻不会抑制因改变[HCO₃⁻]或[Na⁺]而引起的Vbl变化。先前在美西螈近端小管上也进行过类似上述的观察，并归因于一种电中性钠/碳酸氢根共转运机制，该机制使HCO₃⁻、Na⁺和净负电荷同向转运。我们得出结论，泥螈近端小管拥有一种类似（即便不完全相同）的电中性钠/碳酸氢根共转运机制。
