Ingrosso L, Marsigliante S, Zonno V, Storelli C, Vilella S
Laboratorio di Fisiologia Generale e Comparata, Dipartimento di Biologia Università di Lecce, Monteroni 73100 Lecce, Italy.
Am J Physiol Regul Integr Comp Physiol. 2000 Nov;279(5):R1619-24. doi: 10.1152/ajpregu.2000.279.5.R1619.
This study has demonstrated the existence of an L-proline-dependent (Na independent) proton flux at the apical membrane level of the eel intestinal absorbing cells. Using isolated eel enterocytes and the pH-sensitive fluorescent dye 2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF), it was shown that a 20 mM concentration of the imino acid L-proline in the extracellular medium determined an intracellular acidification of approximately 0.28 pH units. However, neither sucrose nor other amino acids were able to significantly acidify the resting intracellular pH. A hyperbolic relationship between extracellular proline concentration and intracellular proton accumulation was observed. Using both isolated brush-border and basolateral membrane vesicles, it was demonstrated that this proline-proton cotransport mechanism was located at the apical membrane level only. In addition, the existence of a coupling mechanism between proline and proton fluxes was demonstrated by the observation that, in brush-border membrane vesicles, the presence of a pH gradient (pH(in) > pH(out)) stimulated the uptake of L-proline.
本研究已证实在鳗鱼肠道吸收细胞的顶端膜水平存在一种L-脯氨酸依赖性（不依赖钠）的质子通量。使用分离的鳗鱼肠上皮细胞和pH敏感荧光染料2'，7'-双（2-羧乙基）-5-（及-6）-羧基荧光素乙酰氧基甲酯（BCECF），结果表明细胞外培养基中20 mM浓度的亚氨基酸L-脯氨酸可使细胞内酸化约0.28个pH单位。然而，蔗糖和其他氨基酸均不能显著酸化静息细胞内pH。观察到细胞外脯氨酸浓度与细胞内质子积累之间呈双曲线关系。使用分离的刷状缘膜囊泡和基底外侧膜囊泡均证实，这种脯氨酸-质子共转运机制仅位于顶端膜水平。此外，通过观察到在刷状缘膜囊泡中pH梯度（pH（内）>pH（外））的存在刺激L-脯氨酸的摄取，证实了脯氨酸与质子通量之间存在偶联机制。
