Mascolo N, Rajendran V M, Binder H J
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Gastroenterology. 1991 Aug;101(2):331-8. doi: 10.1016/0016-5085(91)90008-9.
In this study, the presence of a bicarbonate gradient-dependent, carrier-mediated anion exchange process for butyrate (a representative short-chain fatty acid) uptake in apical membrane vesicles isolated from rat distal colon is described. An outward gradient of both butyrate- and bicarbonate-stimulated [14C]butyrate uptake and resulted in transient accumulation (an "overshoot" phenomenon). Butyrate gradient-stimulated [14C]butyrate uptake was not altered either by an imposed pH gradient or at different pH values. In contrast, bicarbonate gradient-stimulated [14C]butyrate uptake was stimulated severalfold by an additional imposition of an outward pH gradient (pHi = 7.5; pH0 = 6.0). This bicarbonate- and pH gradient-stimulated butyrate uptake was not inhibited by either voltage clamping, with equimolar intravesicular and extravesicular K+ and valinomycin, or 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), an anion-exchange inhibitor. Increasing butyrate concentrations saturated the bicarbonate- and pH gradient-stimulated butyrate uptake with a half-maximal concentration (Km) of 26.9 +/- 1.6 mmol/L. Butyrate uptake was substantially inhibited by 20 mmol/L propionate (45%) and acetate (60%) but was not inhibited by oxalate, inorganic anions (SO4(2-) and NO3-), and transport inhibitors (amiloride, acetazolamide, furosemide, and ouabain). It is concluded from these results that bicarbonate gradient-stimulated butyrate uptake in apical membrane vesicles of rat distal colon occurs via a carrier-mediated anion-exchange process that differs from other DIDS-sensitive anion exchanges [e.g., the Cl- -OH- (HCO3-) process].
在本研究中，描述了从大鼠远端结肠分离的顶端膜囊泡中存在一种依赖于碳酸氢盐梯度、载体介导的丁酸（一种代表性的短链脂肪酸）摄取阴离子交换过程。丁酸和碳酸氢盐的外向梯度均刺激了[14C]丁酸摄取，并导致短暂积累（“过冲”现象）。丁酸梯度刺激的[14C]丁酸摄取不受施加的pH梯度或不同pH值的影响。相比之下，额外施加外向pH梯度（胞内pH = 7.5；胞外pH = 6.0）可使碳酸氢盐梯度刺激的[14C]丁酸摄取增加数倍。这种碳酸氢盐和pH梯度刺激的丁酸摄取不受电压钳制（囊泡内和囊泡外等摩尔的K+和缬氨霉素）或阴离子交换抑制剂4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS）的抑制。增加丁酸浓度可使碳酸氢盐和pH梯度刺激的丁酸摄取饱和，半数最大浓度（Km）为26.9±1.6 mmol/L。20 mmol/L的丙酸盐（45%）和乙酸盐（60%）可显著抑制丁酸摄取，但草酸盐、无机阴离子（SO4(2-)和NO3-）以及转运抑制剂（氨氯吡咪、乙酰唑胺、呋塞米和哇巴因）对其无抑制作用。从这些结果得出的结论是，大鼠远端结肠顶端膜囊泡中碳酸氢盐梯度刺激的丁酸摄取是通过一种载体介导的阴离子交换过程发生的，该过程不同于其他对DIDS敏感的阴离子交换[例如，Cl- -OH-（HCO3-）过程]。
