Linshaw M A, Fogel C A, Downey G P, Koo E W, Gotlieb A I
Department of Pediatrics, Floating Hospital/New England Medical Center, Boston, Massachusetts 02111.
Am J Physiol. 1992 Jan;262(1 Pt 2):F144-50. doi: 10.1152/ajprenal.1992.262.1.F144.
When proximal tubules are immersed in hypotonic medium, they quickly swell to a peak volume. In a second, slower phase, termed volume regulatory decrease (VRD), they shrink as K, anion, and water leave the cells. We investigated the role of the cytoskeleton during this biphasic hypotonic volume regulatory response. Isolated, collapsed rabbit proximal convoluted tubules (PCT) were crimped tightly between two pipettes, and their volume was assessed optically. PCT volume increased to a peak 70-80% above baseline on sudden immersion in dilute medium (150 mosmol/kgH2O). After completing VRD, control tubules had regulated their volume 73 +/- 2% back toward baseline. Tubules exposed to the microtubule inhibitor vincristine (5 microM) regulated 75 +/- 2%. Tubules exposed to the microfilament inhibitor cytochalasin B (50 microM) regulated less (57 +/- 5%), and tubules exposed to both inhibitors regulated only 39 +/- 3% (P less than 0.01 vs. control). Hypotonic VRD was unimpaired in PCT loaded with NaCl by prior exposure to ouabain but was significantly reduced by cytochalasin B. We conclude that VRD is not cation specific and that intact microtubules and microfilaments play a synergistic role in the VRD of rabbit PCT in hyposmotic medium.
当近端小管浸入低渗介质中时，它们会迅速膨胀至峰值体积。在第二个较慢的阶段，即所谓的容积调节性减少（VRD）阶段，随着钾离子、阴离子和水离开细胞，它们会收缩。我们研究了细胞骨架在这种双相低渗容积调节反应中的作用。将分离的、塌陷的兔近端曲小管（PCT）紧紧夹在两个移液管之间，并通过光学方法评估其体积。突然浸入稀释介质（150 mosmol/kgH₂O）中后，PCT体积增加至比基线高出70 - 80%的峰值。完成VRD后，对照小管已将其体积调节至比基线低73±2%。暴露于微管抑制剂长春新碱（5 μM）的小管调节至比基线低75±2%。暴露于微丝抑制剂细胞松弛素B（50 μM）的小管调节程度较小（57±5%），而同时暴露于两种抑制剂的小管仅调节至比基线低39±3%（与对照相比，P＜0.01）。预先用哇巴因处理使PCT加载氯化钠后，低渗VRD不受影响，但细胞松弛素B使其显著降低。我们得出结论，VRD并非阳离子特异性的，并且完整的微管和微丝在低渗介质中兔PCT的VRD中发挥协同作用。
