CHARACTERIZATION OF KINETICS OF PASSIVE AND ACTIVE TRANSPORT MECHANISMS FOR BILE-ACID ABSORPTION IN SMALL-INTESTINE AND COLON OF RAT
CHARACTERIZATION OF KINETICS OF PASSIVE AND ACTIVE TRANSPORT MECHANISMS FOR BILE-ACID ABSORPTION IN SMALL-INTESTINE AND COLON OF RAT
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DOI：
10.1172/jci106931
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发表时间：
1972-01-01
影响因子：
15.9
通讯作者：
DIETSCHY, JM
中科院分区：
文献类型：
--
作者：
SCHIFF, ER;SMALL, NC;DIETSCHY, JM
胆汁酸摄取通过在肠的所有区域中的被动扩散和通过在回肠中的主动吸收发生。离子化单体（*P-）的被动渗透系数的测定表明，渗透性分别降低了3.4，6.8和8.1倍的羟基，甘氨酸，或牛磺酸基团，添加到类固醇核。去除负电荷增加渗透的一个因素的4.4，然而，质子化单体的渗透系数显示出相同的相对减少与添加的羟基。与这些添加物相关的溶液的计算增量自由能（δΔFW→1）等于+ 757（羟基），+ 1178（甘氨酸）和+ 1291（牛磺酸）cal/mole。横结肠的被动渗透系数显示了各种胆汁酸之间相同的相对关系。对回肠的被动渗透性进行适当校正后，测量主动转运系统的最大转运速度（*Vmax）和米氏常数（*Km）的表观值。Vmax取决于类固醇核上羟基的数量;三羟基胆汁酸的值较高（1543-1906 pmol/min/cm），而二羟基（114-512 pmol/min/cm）和一羟基（45-57 pmol/min/cm）酸的值较低。相反，* Km值与胆汁酸是否结合有关;未结合胆汁酸的值范围为0.37 - 0.49 mM，而结合胆汁酸的值约为一半（0.12-0.23 mM）。
Bile acid uptake occurs via passive diffusion in all regions of the intestine and via active absorption in the ileum. Determination of the passive permeability coefficient for ionized monomers (*P-) demonstrated that permeability decreased by a factor of 3.4, 6.8, and 8.1 for the addition of a hydroxyl, glycine, or taurine group, respectively, to the steroid nucleus. Removal of the negative charge increased permeation by a factor of 4.4; however, permeability coefficients for the protonated monomers showed the same relative decrease with addition of a hydroxyl group. The calculated incremental free energies of solution (δΔFW→1) associated with these additions equaled + 757 (hydroxyl), + 1178 (glycine), and + 1291 (taurine) cal/mole. Passive permeability coefficients for the transverse colon showed the same relative relationships among the various bile acids. After making appropriate corrections for passive permeability across the ileum, apparent values for the maximal transport velocity (*Vmax) and Michaelis constant (*Km) of the active transport system were measured.*Vmaxdepended upon the number of hydroxyl groups on the steroid nucleus; values for the trihydroxy bile acids were high (1543-1906 pmoles/min per cm) while those for the dihydroxy (114-512 pmoles/min per cm) and monohydroxy (45-57 pmoles/min per cm) acids were lower. In contrast,*Kmvalues were related to whether the bile acid was conjugated; unconjugated bile acids had values ranging from 0.37 to 0.49 mM, while values for the conjugated bile acids were approximately half as high (0.12-0.23 mM).