Charney A N, Micic L, Egnor R W
Nephrology Section, Veterans Affairs Medical Center, New York University School of Medicine, New York 10010, USA.
Am J Physiol. 1998 Mar;274(3):G518-24. doi: 10.1152/ajpgi.1998.274.3.G518.
Short-chain fatty acid (SCFA) transport across the colon may occur by nonionic diffusion and/or via apical membrane SCFA-/HCO3- exchange. To examine the relative importance of these processes, stripped segments of rat (Ratus ratus) proximal and distal colon were studied in Ussing chambers, and the unidirectional fluxes of radiolabeled SCFA butyrate, propionate, or weakly metabolized isobutyrate were measured. In N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) or 1 or 5 mM HCO3- Ringer, decreases in mucosal pH stimulated mucosal-to-serosal flux (Jm-->s) of all SCFA, decreases in serosal pH stimulated serosal-to-mucosal flux (Js-->m), and bilateral pH decreases stimulated both fluxes equally. These effects were observed whether the SCFA was present on one or both sides of the tissue, in both proximal and distal colon, in the absence of luminal Na+, and in the presence of either luminal or serosal ouabain. Changes in intracellular pH or intracellular [HCO3-] did not account for the effects of extracellular pH. Luminal Cl- removal, to evaluate the role of apical membrane Cl-/SCFA- exchange, had no effect on Jm-->s but decreased Js-->m 32% at pH 6.5 and 22% at 7.2. Increasing SCFA concentration from 1 to 100 mM, at pH 6.4 or 7.4, caused a linear increase in Jm-->s. We conclude that SCFA are mainly transported across the rat colon by nonionic diffusion.
短链脂肪酸（SCFA）穿过结肠的过程可能通过非离子扩散和/或经由顶端膜SCFA⁻/HCO₃⁻交换来实现。为了研究这些过程的相对重要性，在尤斯灌流小室中对大鼠（褐家鼠）近端和远端结肠的剥离段进行了研究，并测量了放射性标记的SCFA丁酸、丙酸或代谢较弱的异丁酸的单向通量。在N-2-羟乙基哌嗪-N'-2-乙磺酸（HEPES）或1或5 mM HCO₃⁻林格液中，黏膜pH值降低会刺激所有SCFA的黏膜到浆膜通量（Jm→s），浆膜pH值降低会刺激浆膜到黏膜通量（Js→m），而双侧pH值降低则会同等程度地刺激这两种通量。无论SCFA存在于组织的一侧还是两侧，在近端和远端结肠中，在无管腔Na⁺的情况下，以及在存在管腔或浆膜哇巴因的情况下，均观察到这些效应。细胞内pH值或细胞内[HCO₃⁻]的变化并不能解释细胞外pH值的影响。去除管腔Cl⁻以评估顶端膜Cl⁻/SCFA⁻交换的作用，对Jm→s没有影响，但在pH 6.5时使Js→m降低32%，在pH 7.2时降低22%。在pH 6.4或7.4时，将SCFA浓度从1 mM增加到100 mM会导致Jm→s呈线性增加。我们得出结论，SCFA主要通过非离子扩散穿过大鼠结肠。
