Frigeri A, Gropper M A, Umenishi F, Kawashima M, Brown D, Verkman A S
Department of Medicine, University of California, San Francisco 94143-0521, USA.
J Cell Sci. 1995 Sep;108 ( Pt 9):2993-3002. doi: 10.1242/jcs.108.9.2993.
It was shown recently that water channel homologs MIWC (mercurial insensitive water channel) and GLIP (glycerol intrinsic protein) colocalized in basolateral membranes of kidney collecting duct, tracheal and colonic epithelia, and in brain pia mater. We report here an extensive immunolocalization study of MIWC and GLIP in non-epithelial and glandular epithelial tissues in rat. Immunogold electron microscopy confirmed colocalization of MIWC and GLIP in basolateral membrane of principal cells in kidney collecting duct. However, in other epithelia, MIWC but not GLIP was expressed in basolateral membrane of parietal cells in stomach, and in excretory tubules of salivary and lacrimal glands; GLIP but not MIWC was expressed in transitional epithelium of urinary bladder and skin epidermis. In the central nervous system, MIWC was strongly expressed in the ependymal layer lining the aqueductal system, and in astrocytes throughout the spinal cord and in selected regions of brain. MIWC was also expressed in a plasma membrane pattern in skeletal, but not smooth or cardiac muscle. Neither protein was expressed in small intestine, testis, liver, spleen and nerve. The tissue-specific expression of MIWC suggests a role in fluid transport and/or cell volume regulation in stomach and glandular epithelia. The functional role of MIWC expression in the neuromuscular system and of GLIP expression in skin and urinary bladder is uncertain. The specific cellular sites of MIWC expression (astrocytes, trachea, sarcolemma, gastric parietal cells and kidney principal cells) correspond exactly to sites where orthogonal arrays of particles (OAPs) have been visualized by freeze-fracture electron microscopy, suggesting that MIWC may be the OAP protein.
最近研究表明，水通道同源物MIWC（汞不敏感水通道）和GLIP（甘油内在蛋白）共定位于肾集合管、气管和结肠上皮细胞的基底外侧膜以及脑软脑膜中。我们在此报告一项关于大鼠非上皮和腺上皮组织中MIWC和GLIP的广泛免疫定位研究。免疫金电子显微镜证实了MIWC和GLIP在肾集合管主细胞基底外侧膜中共定位。然而，在其他上皮组织中，MIWC在胃壁细胞的基底外侧膜以及唾液腺和泪腺的排泄小管中表达，而GLIP不表达；GLIP在膀胱移行上皮和皮肤表皮中表达，而MIWC不表达。在中枢神经系统中，MIWC在导水管系统内衬的室管膜层、脊髓和脑特定区域的星形胶质细胞中强烈表达。MIWC在骨骼肌的质膜上也有表达模式，但在平滑肌或心肌中不表达。在小肠、睾丸、肝脏、脾脏和神经中均未检测到这两种蛋白的表达。MIWC在组织中的特异性表达表明其在胃和腺上皮的液体运输和/或细胞体积调节中发挥作用。MIWC在神经肌肉系统中的功能作用以及GLIP在皮肤和膀胱中的功能作用尚不清楚。MIWC表达的特定细胞位点（星形胶质细胞、气管、肌膜、胃壁细胞和肾主细胞）与通过冷冻断裂电子显微镜观察到的正交颗粒阵列（OAPs）的位点完全对应，这表明MIWC可能就是OAP蛋白。
