Vidal G, Durand T, Canioni P, Gallis J L
Résonance Magnétique des Systèmes Biologiques, UMR 5536 CNRS/Université Victor Segalen Bordeaux 2, France.
Biochim Biophys Acta. 1998 Sep 16;1425(1):224-34. doi: 10.1016/s0304-4165(98)00075-0.
The contribution of metabolic bicarbonate to cytosolic pH (pHcyto) regulation was studied on isolated perfused rat liver using phosphorus-31 NMR spectroscopy. Removal of external HCO3- decreased proton efflux from 18.6+/-5.0 to 1.64+/-0.29 micromol/min per g liver wet weight (w.w.) and pHcyto from 7.17+/-0.06 to 6.87+/-0.06. In the nominal absence of bicarbonate, inhibition of carbonic anhydrase by acetazolamide induced a further decrease of proton efflux of 0.69+/-0.26 micromol/min per g liver w.w. reflecting a reduction in metabolic CO2 hydration, and hence a decrease of H+ and HCO3- supplies. Even though 27% of the proton efflux was amiloride-sensitive under bicarbonate-free conditions, amiloride did not change pHcyto, revealing the contribution of additional regulatory processes. Indeed, pH regulation was affected by the combined use of 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and amiloride since pHcyto decreased by 0.16+/-0.05 and proton efflux by 0.60+/-0.14 micromol/min per g liver w.w. The data suggest that amiloride-sensitive or SITS-sensitive transport activities could achieve, by themselves, pHcyto regulation. The involvement of two mechanisms, most likely Na+/H+ antiport and Na+:HCO3 symport, was confirmed in the whole organ under intracellular and extracellular acidosis. The evidence of Na-dependent transport of HCO3- in the absence of exogenous bicarbonate implies that the amount of metabolic bicarbonate is sufficient to effectively participate to pHcyto regulation.
利用磷-31核磁共振波谱法，在离体灌注大鼠肝脏上研究了代谢性碳酸氢盐对细胞内pH（pHcyto）调节的作用。去除细胞外HCO3-后，质子流出量从每克肝脏湿重（w.w.）18.6±5.0微摩尔/分钟降至1.64±0.29微摩尔/分钟，pHcyto从7.17±0.06降至6.87±0.06。在名义上不存在碳酸氢盐的情况下，乙酰唑胺抑制碳酸酐酶导致质子流出量进一步降低，每克肝脏湿重为0.69±0.26微摩尔/分钟，这反映了代谢性CO2水合作用的降低，从而导致H+和HCO3-供应减少。尽管在无碳酸氢盐条件下27%的质子流出对氨氯地平敏感，但氨氯地平并未改变pHcyto，这揭示了其他调节过程的作用。实际上，4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸（SITS）和氨氯地平联合使用会影响pH调节，因为pHcyto降低了0.16±0.05，质子流出量降低了每克肝脏湿重0.60±0.14微摩尔/分钟。数据表明，氨氯地平敏感或SITS敏感的转运活性自身即可实现pHcyto调节。在细胞内和细胞外酸中毒的整个器官中，证实了两种机制（最可能是Na+/H+反向转运和Na+:HCO3同向转运）的参与。在没有外源性碳酸氢盐的情况下，Na依赖性HCO3-转运的证据表明，代谢性碳酸氢盐的量足以有效参与pHcyto调节。
