Significance: Vasopressin is a peptide hormone that regulates renal water excretion to maintain whole-body water balance. It does so by regulating trafficking of a molecular water channel, aquaporin-2, to and from the plasma membrane of collecting duct cells. This study uses two state-of-the-art methods (protein mass spectrometry of affinity-isolated apical plasma membrane proteins and live-cell imaging of actin dynamics) to uncover the central role of the actin dynamics in the trafficking of aquaporin-2–containing vesicles. The results coupled with prior data produce a model in which vasopressin signaling triggers actin accumulation near the tight junction and concomitant depletion of actin from the central regions of the apical plasma membrane, thereby providing access of aquaporin-2–containing vesicles to the apical plasma membrane.

Background: Lauge-Hansen supination-external rotation Stage IV ankle injuries may simulate a Stage II or Stage III injury radiographically if the medial disruption occurred through the deltoid ligament instead of the medial malleolus, making it difficult to determine whether an operation is indicated. Materials and Methods: Seventeen patients presented with radiographically isolated lateral malleolar fractures at the syndesmotic level. They were examined with ultrasonography for evaluation of the integrity of the deltoid ligament. Patients in whom ultrasonography showed complete rupture of the deltoid ligament received operative fixation of the ankle fracture, with exploration and repair of the deltoid ligament at the same time. Patients without complete rupture of the deltoid ligament were treated conservatively with a short leg cast for 6 weeks followed by an ankle brace for another 6 weeks. Nine male and six female patients completed the final clinical and radiographic evaluations. Results: Ultrasonography showed complete rupture of the deltoid ligament in six patients. Exploration of the deltoid ligaments confirmed the sonographic findings in all these patients. In the remaining nine patients, the deltoid ligaments were not completely ruptured on ultrasound. These fractures were treated conservatively, and all healed uneventfully. All the 15 patients had good or fair results on the final evaluation. Conclusion: Ultrasonography is a convenient and accurate diagnostic tool to differentiate unstable bimalleolar-equivalent ankle fractures from an isolated lateral malleolar fracture. Thus, it can be helpful in the decision process for the treatment of choice for different fracture patterns.