O'Donnell M J, Maddrell S H, Gardiner B O
Am J Physiol. 1984 May;246(5 Pt 2):R759-69. doi: 10.1152/ajpregu.1984.246.5.R759.
The walls of isolated upper Malpighian tubules of the insect, Rhodnius prolixus, are much more permeable to small relatively unchanged solutes (ethanol, xylose, and mannitol) than to larger or more charged solutes (acetate, glycine, tyrosine, and inulin). The more permeable solutes rapidly reach concentrations in the tubule cells equivalent to their concentrations in the bathing medium; the less permeable solutes do not penetrate into the cells. The time course of accumulation of permeable solute in the cells matches the time course of the appearance of solute in the lumen. Substances injected into the hemolymph of fed R. prolixus appear in the urine at concentrations predictable from the permeability of in vitro tubules, supporting the idea that the in vitro permeability of the tubules is representative of their properties in the intact insect. It is suggested that the rapid transcellular penetration of small solutes through the Malpighian tubules reflects the large areas of cell membrane. The area of cell membrane exceeds that of the paracellular clefts by a factor of 10(5).
昆虫红带锥蝽（Rhodnius prolixus）分离的上段马尔皮基氏小管的管壁，对相对未发生变化的小分子溶质（乙醇、木糖和甘露醇）的通透性，比对大分子或带更多电荷的溶质（乙酸盐、甘氨酸、酪氨酸和菊粉）的通透性高得多。通透性较高的溶质能迅速在小管细胞内达到与其在浴液中的浓度相当的浓度；而通透性较低的溶质则不会渗入细胞。细胞内可通透溶质的积累时间进程与溶质在管腔中出现的时间进程相匹配。注入饱食的红带锥蝽血淋巴中的物质，会以根据体外小管通透性可预测的浓度出现在尿液中，这支持了小管的体外通透性代表其在完整昆虫体内特性的观点。有人提出，小分子溶质通过马尔皮基氏小管的快速跨细胞渗透反映了细胞膜的大面积。细胞膜面积比细胞旁间隙面积大10^5倍。
