Aquaporins are membrane water channel proteins through which water permeates the lipid bilayer. So far 13 aquaporin isoforms, aquaporin-0 (AQP0) to AQP12, have been identified in mammals. They are classified into 3 subgroups: 1) aquaporins that selectively transfer water, 2) aquaglyceroporins that transfer some small solutes as well as water, and 3) unorthodox aquaporins. They are widely distributed in most water-handling organs, such as kidney, and play important roles in water transfer. For example, segment-specific expression of AQP1, AQP2, AQP3, AQP4, AQP6, AQP7, and AQP11 in the renal tubular epithelium enables water reabsorption to produce concentrated urine. Aquaporins are usually localized to the plasma membrane. Some isoforms, such as AQP2, are present in the intracellular membrane compartment. AQP2 in collecting duct cells translocates between intracellular vesicles and the cell surface via a membrane trafficking mechanism. Mutations of AQP2 result in congenital nephrogenic diabetes insipidus. This review summarizes the distribution and physiological importance of aquaporins, with a special focus on the kidney.

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In Japan, the prevalence of vertebral fractures, which increases with age, is about 10% in persons in their 60s and 35% in persons in their 70s. Vertebral fracture is considered a fragility fracture, which can be caused even by minor trauma. Diagnosis tends to be difficult with plain x-ray films, and computed tomography and magnetic resonance are likely to be helpful. Prognoses are particularly poor in cases with low bone density, cases with fractures at the transition from thoracic to lumbar vertebrae, cases with injury to the posterior walls, and cases in which treatment is delayed. The most important issue is fracture prevention by appropriately treating osteoporosis. When fracture does occur, it must be diagnosed early and treated effectively.

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The capsule endoscope (CE) and the double-balloon endoscope (DBE), were developed to visualize the entire small intestine, have substantially altered diagnostic options in patients with small intestinal diseases. The CE provides clear, natural images of the entire small intestine and allows for the visualization of even minute lesions, such as solitary red spots and minor erosions. However, the major disadvantages of the CE are that it sometimes fails to reach the cecum, can become trapped in the intestine, and does not allow biopsy or treatment. The DBE can reach beyond the ligament of Treitz when inserted orally, and can reach beyond the ileocecal valve when inserted anally; therefore, real-time visualization of the entire small intestine is possible when the oral and anal approaches are combined. The DBE provides sharp endoscopic images, but its main advantage lies in its four-directional angle of operation and special instrument channel that allow both directed biopsies and treatments, such as the resection of polyps and the dilation of strictures. However, the major disadvantages of examination with the DBE when compared with the CE are that it requires sedation, often requires fluoroscopy, and cannot be performed without additional support staff. Therefore, the CE can be used to screen for small intestinal pathologies, and the DBE can be used for the optimal diagnosis and treatment of these diseases. Both the CE and DBE should be established as gold standards in the diagnosis and treatment of small intestinal lesions.

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Histochemistry, especially immunohistochemistry, is a powerful and diverse set of methods for obtaining spatial and temporal information concerning the expression and distribution of biomolecules in situ. In this technical note, we describe procedures for fixation and immunofluorescence microscopy using cryostat sections.

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