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Original Article

Microfilament Network Is Needed for the Endocytosis of Water Channels and Not for Apical Membrane Insertion Upon Vasopressin Action

Adnan Dibas^*,1, Abdul Mia and Thomas Yorio

^* Mary Kay Ash Institute for Cancer Research, Dallas, Texas 75235;
Jarvis Christian College, Hawkins, Texas 75765; and
Department of Pharmacology, University of North Texas Health Science Center at Fort Worth, Fort Worth, Texas 76107

In the current study, a novel role for the microfilaments in vasopressin-induced water transport in toad urinary bladders, a popular model for the mammalian collecting duct, was established. Vasopressin-induced water transport was not affected by cytochalasin D (CD, 20 µM) or latrunculin B (Lat B, 0.5–2 µM), microfilament-disrupting reagents, suggesting that the initial trafficking of vesicles containing water channels and insertion of membranes into the apical membrane are microfilament-independent. After the removal of vasopressin, bladders treated with CD or Lat B continued to transport water at least 2–3-fold greater than those that received the vehicle. Furthermore, the enhanced water transport was inhibited by HgCl₂ (1 mM), a potent inhibitor of water channel–mediated water flow, suggesting that the enhanced water flow was through water channels. In addition, Lat B and CD inhibited vasopressin-induced endocytosis of horseradish peroxidase (HRP), a fluid endocytotic marker. These results suggested that although microfilaments are not needed for the initial trafficking of water channels to the apical side, the microfilament network is essential for the retrieval of water channels following their insertion into apical membranes.

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