Dagher P C, Behm T, Taglietta-Kohlbrecher A, Egnor R W, Charney A N
Nephrology Section, Veterans Affairs Medical Center, New York, New York 10010, USA.
Am J Physiol. 1996 Jun;270(6 Pt 1):C1799-806. doi: 10.1152/ajpcell.1996.270.6.C1799.
Intracellular acidification by stimuli rather than CO2 fails to stimulate colonic apical Na/H ex-change and Na absorption. We examined whether Na absorption could be stimulated in the absence of changes in cytoplasmic pH (pHi). Distal colon of male Sprague-Dawley rats was used for pHi measurements with 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein and for flux measurements in Ussing chambers. In 21 mM HCO3-Ringer, increasing PCO2 from 20 to 70 mmHg decreased pHi from 7.51 to 7.03 and increased net Na flux (JnetNa) from 4.2 +/- 0.4 to 6.8 +/- 0.6 mu eq.cm-2.h-1. Similar increases in JnetNa occurred in the absence of mucosal CI and in the presence of phalloidin to inhibit microfilaments or penzolamide to inhibit membrane-bound carbonic anhydrase. sohydric increases in Pco2 did not alter pHi but stimulated JnetNa from 5.1 +/- 0.6 to 7.2 +/- 0.8 mu eq.cm-2.h-1. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) decreased pHi from 7.45 to 7.35 but did not stimulate JnetNa. Butyrate (25 mM) decreased pHi from 7.15 to 7.02 with recovery to baseline within 6 min; however, JnetNa increased by 2.2 mu eq.cm-2.h-1 for 60 min. We conclude that apical Na/H exchange activity is unresponsive to changes in bulk pHi and is independent of Cl/HCO3 exchange, microfilaments, and membrane-bound carbonic anhydrase. The presence of an H-tight, CO2, and butyrate-permeable subapical domain is postulated.
由刺激而非二氧化碳引起的细胞内酸化无法刺激结肠顶端钠/氢交换和钠吸收。我们研究了在细胞质pH（pHi）无变化的情况下钠吸收是否能被刺激。雄性Sprague-Dawley大鼠的远端结肠用于用2',7'-双（羧乙基）-5（6）-羧基荧光素进行pHi测量，并用于在尤斯灌流小室中进行通量测量。在21 mM碳酸氢根林格液中，将PCO2从20 mmHg增加到70 mmHg可使pHi从7.51降至7.03，并使净钠通量（JnetNa）从4.2±0.4增加到6.8±0.6 μeq·cm-2·h-1。在无黏膜氯离子以及存在抑制微丝的鬼笔环肽或抑制膜结合碳酸酐酶的苯并酰胺的情况下，JnetNa也出现类似增加。等氢离子浓度增加Pco2并未改变pHi，但将JnetNa从5.1±0.6刺激到7.2±0.8 μeq·cm-2·h-1。羰基氰化物间氯苯腙（CCCP）使pHi从7.45降至7.35，但未刺激JnetNa。丁酸盐（25 mM）使pHi从7.15降至7.02，并在（6分钟内恢复到基线；然而，JnetNa在60分钟内增加了2.2 μeq·cm-2·h-1。我们得出结论，顶端钠/氢交换活性对总体pHi的变化无反应，且独立于氯/碳酸氢根交换、微丝和膜结合碳酸酐酶。推测存在一个对氢离子紧密、对二氧化碳和丁酸盐通透的顶端下区域。
