Sofía Hernández C, González E, Whittembury G
Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela.
J Membr Biol. 1995 Dec;148(3):233-42. doi: 10.1007/BF00235041.
Lumen to bath J12/C1 and bath to lumen J21/C2 fluxes per unit concentration of 19 probes with diameters (dm) ranging from 3.0-30.0 A (water, urea, erythritol, mannitol, sucrose, raffinose and 13 dextrans with dm 9.1-30.0 A) were measured during volume secretion (Jv) in the upper segment of the Malpighian Tubule of Rhodnius by perfusing lumen and bath with 14C or 3H-labeled probes. Jnet = (J12/C1-J21/C2) was studied as a function of Jv.Jv was varied by using different concentrations of 5-hydroxy tryptamine. Jnet for 3H-water was not different from Jv. We found: (i) A strong correlation between Jnet and Jv for 8 probes dm = 3.0-11.8 A (group a probes), indicating that the convective component of Jnet is more important than its diffusive component and than unstirred layers effects which are negligible. Therefore group a probes are solvent dragged as they cross the epithelium. (ii) There is no correlation between Jnet and Jv for 11 probes with dm = 11.8-30 A (group b). Therefore these probes must cross the epithelium by diffusion and not by solvent drag. (iii) In a plot of Jnet/Jv vs. dm group a probes show a steep linear relation with a slope = -0.111, while for group b probes the slope is -0.002. Thus there is a break between groups a and b in this plot. We tried to fit the data with models for restricted diffusion and convention through cylindrical or parallel slit pathways. We conclude that (i) group a probes are dragged by water through an 11.0 A-wide slit. (ii) Most of Jv must follow an extracellular noncytosolic pathway. (iii) Group b probes must diffuse through a 42 A-wide slit. (iv) A cylindrical pathway does not fit the data.
通过用(^{14}C)或(^{3}H)标记的探针灌注管腔和浴液，在红蝽马氏管上段的容积分泌（(Jv)）过程中，测量了19种直径（(dm)）范围为(3.0 - 30.0\mathring{A})的探针（水、尿素、赤藓糖醇、甘露醇、蔗糖、棉子糖以及13种(dm)为(9.1 - 30.0\mathring{A})的右旋糖酐）的单位浓度下管腔到浴液的(J12/C1)通量和浴液到管腔的(J21/C2)通量。研究了(Jnet = (J12/C1 - J21/C2))作为(Jv)的函数。通过使用不同浓度的5 - 羟色胺来改变(Jv)。(^{3}H) - 水的(Jnet)与(Jv)无差异。我们发现：（i）对于8种(dm = 3.0 - 11.8\mathring{A})的探针（a组探针），(Jnet)与(Jv)之间存在强相关性，这表明(Jnet)的对流成分比其扩散成分以及可忽略不计的非搅拌层效应更重要。因此，a组探针在穿过上皮时是被溶剂拖拽的。（ii）对于11种(dm = 11.8 - 30\mathring{A})的探针（b组），(Jnet)与(Jv)之间不存在相关性。因此，这些探针必定是通过扩散而非溶剂拖拽穿过上皮的。（iii）在(Jnet/Jv)对(dm)的图中，a组探针呈现出斜率为(-0.111)的陡峭线性关系，而b组探针的斜率为(-0.002)。因此，在此图中a组和b组之间存在断点。我们尝试用通过圆柱形或平行狭缝路径的受限扩散和对流模型来拟合数据。我们得出结论：（i）a组探针被水通过一个(11.0\mathring{A})宽的狭缝拖拽。（ii）大部分(Jv)必定遵循细胞外非胞质途径。（iii）b组探针必定通过一个(42\mathring{A})宽的狭缝扩散。（iv）圆柱形路径不适合这些数据。
