Dagher G, Thomas S R, Griffiths N, Siaume-Perez S, Sauterey C
Laboratoire de Physiologie Cellulaire, Collége de France, Paris, France.
Am J Physiol. 1997 Jul;273(1 Pt 2):F97-103. doi: 10.1152/ajprenal.1997.273.1.F97.
Calcitonin is known to stimulate Ca2+ reabsorption and natriuresis and to increase adenosine 3',5'-cyclic monophosphate levels in early distal tubule, but its effects on acid-base transport mechanisms are not well characterized in this segment. We found that recovery of cell pH (pH1) from an induced acid load (using NH4+) in single isolated segments of the initial portion ("bright") of the rabbit distal convoluted tubule (DCTb) was due to an ethylisopropylamiloride-sensitive Na+/H+ exchanger both in the absence and presence of HCO3-, but we found no evidence for participation of other mechanisms such as an H+ pump or an HCO3(-)-dependent mechanism. Introduction of calcitonin stimulated an Na(+)-independent, HCO3(-)-dependent mechanism (0.17 +/- 0.04 pH units/min, n = 14) that reestablishes normal pHi after an induced acid load. This mechanism was observed only in the presence of CO2/HCO3- and was not inhibited by N-ethylmaleimide (1 mM), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (200 microM), or Sch-28080 nor stimulated by glutamine (2 mM) or ketoglutarate (0.5 mM), but it was dependent on chloride. We conclude that, in the DCTb, salmon calcitonin activates a latent Na(+)-independent, HCO3(-)-dependent mechanism.
已知降钙素可刺激钙离子重吸收和利钠作用，并增加远端小管起始段的3',5'-环磷酸腺苷水平，但该段对酸碱转运机制的影响尚未完全明确。我们发现，在兔远端曲管起始部（“明亮部”，DCTb）的单个分离节段中，从诱导酸负荷（使用NH4+）中恢复细胞内pH（pHi）是由于存在和不存在HCO3-时均有对乙基异丙基氨氯地平敏感的Na+/H+交换体，但未发现其他机制如H+泵或HCO3-依赖机制参与的证据。引入降钙素可刺激一种不依赖Na+、依赖HCO3-的机制（0.17±0.04 pH单位/分钟，n = 14），该机制在诱导酸负荷后可重新建立正常的pHi。此机制仅在存在CO2/HCO3-时观察到，不受N-乙基马来酰亚胺（1 mM）、4,4'-二异硫氰基芪-2,2'-二磺酸（200 microM）或Sch-28080抑制，也不受谷氨酰胺（2 mM）或酮戊二酸（0.5 mM）刺激，但依赖于氯离子。我们得出结论，在DCTb中，鲑鱼降钙素激活了一种潜在的不依赖Na+、依赖HCO3-的机制。
