Muto Shigeaki, Tsuruoka Shuichi, Miyata Yukio, Fujimura Akio, Kusano Eiji, Wang Wenhui, Seldin Donald, Giebisch Gerhard
Department of Nephrology, Jichi Medical University, Shimotsuke, Tochigi, Japan.
Kidney Int. 2009 Jan;75(1):25-30. doi: 10.1038/ki.2008.447. Epub 2008 Sep 3.
Stimulation of the basolateral Na(+)/K(+)-ATPase in the isolated perfused rabbit cortical collecting duct by raising either bath potassium or lumen sodium increases potassium secretion, sodium absorption and their apical conductances. Here we determined the effect of stimulating Na(+)/K(+)-ATPase on potassium secretion without luminal sodium transport. Acutely raising bath potassium concentrations from 2.5 to 8.5 mM, without luminal sodium, depolarized the basolateral membrane and transepithelial voltages while increasing the transepithelial, basolateral and apical membrane conductances of principal cells. Fractional apical membrane resistance and cell pH were elevated. Net potassium secretion was maintained albeit diminished and was still enhanced by raising bath potassium, but was reduced by basolateral ethylisopropylamiloride, an inhibitor of Na(+)/H(+) exchange. Luminal iberitoxin, a specific inhibitor of the calcium-activated big-conductance potassium (BK) channel, impaired potassium secretion both in the presence and absence of luminal sodium. In contrast, iberitoxin did not affect luminal sodium transport. We conclude that basolateral Na(+)/H(+) exchange in the cortical collecting duct plays an important role in maintaining potassium secretion during compromised sodium supplies and that BK channels contribute to potassium secretion.
通过提高灌流液钾离子浓度或管腔钠离子浓度来刺激离体灌注兔皮质集合管的基底外侧钠钾ATP酶，可增加钾离子分泌、钠离子重吸收及其顶端电导。在此，我们确定了在无管腔钠转运情况下刺激钠钾ATP酶对钾离子分泌的影响。在无管腔钠的情况下，将灌流液钾离子浓度从2.5 mM急剧提高到8.5 mM，使基底外侧膜和跨上皮电压去极化，同时增加主细胞的跨上皮、基底外侧和顶端膜电导。顶端膜电阻分数和细胞pH值升高。尽管净钾离子分泌减少，但仍得以维持，且通过提高灌流液钾离子浓度仍可增强，但基底外侧钠氢交换抑制剂乙基异丙基氨氯吡咪可使其降低。管腔iberitoxin（一种钙激活大电导钾离子（BK）通道的特异性抑制剂）在有和无管腔钠的情况下均损害钾离子分泌。相比之下，iberitoxin不影响管腔钠转运。我们得出结论，皮质集合管中的基底外侧钠氢交换在钠供应受损时维持钾离子分泌中起重要作用，且BK通道有助于钾离子分泌。
