Levine S, Franki N, Hays R M
J Clin Invest. 1973 Jun;52(6):1435-42. doi: 10.1172/JCI107317.
It is generally believed that urea crosses the cell membrane through aqueous channels, and that its movement across the membrane is accelerated in the direction of net water flow (solvent drag effect). The present report presents evidence for a vasopressin-sensitive pathway for the movement of urea, other amides, and certain non-amides, which is independent of water flow. Phloretin, when present at 10(-4) M concentration in the medium bathing the luminal surface of the toad bladder, strongly inhibits the movement of urea, acetamide, and propionamide across the toad bladder, both in the absence and presence of vasopressin. The vasopressin-stimulated movement of formaldehyde and thiourea is also reduced. Osmotic water flow, on the other hand, is not affected; nor is the movement of ethanol and ethylene glycol, or the net transport of sodium. On the basis of these studies we would conclude that the movement of many, if not all, solutes across the cell membrane is independent of water flow, and that a vasopressin-sensitive carrier may be involved in the transport of certain solutes across the cell membrane.
一般认为，尿素通过水通道穿过细胞膜，并且其跨膜移动在净水流方向上加速（溶剂拖曳效应）。本报告提供了证据，证明尿素、其他酰胺类以及某些非酰胺类物质存在一条对血管加压素敏感的移动途径，该途径与水流无关。当在蟾蜍膀胱管腔表面的浴液中以10⁻⁴ M的浓度存在时，根皮素强烈抑制尿素、乙酰胺和丙酰胺在蟾蜍膀胱中的移动，无论有无血管加压素。血管加压素刺激的甲醛和硫脲的移动也减少。另一方面，渗透水流不受影响；乙醇和乙二醇的移动以及钠的净转运也不受影响。基于这些研究，我们可以得出结论，许多（如果不是全部）溶质跨细胞膜的移动与水流无关，并且血管加压素敏感载体可能参与某些溶质跨细胞膜的转运。
