Carpi-Medina P, González E, Whittembury G
Am J Physiol. 1983 May;244(5):F554-63. doi: 10.1152/ajprenal.1983.244.5.F554.
Cell osmotic water permeability, Pcos, of the peritubular aspect of the proximal convoluted tubule (PCT) was measured from the time course of cell volume changes subsequent to the sudden imposition of an osmotic gradient, delta Cio, across the cell membrane of PCT that had been dissected and mounted in a chamber. The possibilities of artifact were minimized. The bath was vigorously stirred, the solutions could be 95% changed within 0.1 s, and small osmotic gradients (10-20 mosM) were used. Thus, the osmotically induced water flow was a linear function of delta Cio and the effect of the 70-microns-thick unstirred layers was negligible. In addition, data were extrapolated to delta Cio = 0. Pcos for PCT was 41.6 (+/- 3.5) X 10(-4) cm3 X s-1 X osM-1 per cm2 of peritubular basal area. The standing gradient osmotic theory for transcellular osmosis is incompatible with this value. Published values for Pcos of PST are 25.1 X 10(-4), and for the transepithelial permeability Peos values are 64 X 10(-4) for PCT and 94 X 10(-4) for PST, in the same units. These results indicate that there is room for paracellular water flow in both nephron segments and that the magnitude of the transcellular and paracellular water flows may vary from one segment of the proximal tubule to another.
通过对解剖并置于小室中的近端曲管（PCT）细胞膜两侧突然施加渗透梯度（δCio）后细胞体积变化的时间进程，来测量PCT肾小管周侧的细胞渗透水通透性（Pcos）。将人为因素的可能性降至最低。对浴液进行剧烈搅拌，溶液可在0.1秒内95%更换，并使用小的渗透梯度（10 - 20 mosM）。因此，渗透诱导的水流是δCio的线性函数，70微米厚的未搅拌层的影响可忽略不计。此外，数据外推至δCio = 0。PCT的Pcos为每平方厘米肾小管周基底面积41.6（±3.5）×10⁻⁴ cm³×s⁻¹×osM⁻¹。跨细胞渗透的立位梯度渗透理论与该值不相符。以相同单位计，已发表的PST的Pcos值为25.1×10⁻⁴，PCT的跨上皮通透性Peos值为64×10⁻⁴，PST的为94×10⁻⁴。这些结果表明，在两个肾单位节段中都存在细胞旁水流的空间，并且跨细胞和细胞旁水流的大小可能在近端小管的不同节段之间有所变化。
