title: An approach to the research on ion and water properties in the interphase between the plasma membrane and bulk extracellular solution.
abstract: In vivo, cells are immersed in an extracellular solution that contains a variety of bioactive substances including ions and water. Classical electrophysiological analyses of epithelial cells in the stomach and small intestine have revealed that within a distance of several hundred micrometers above their apical plasma membrane, lies an extracellular layer that shows ion concentration gradients undetectable in the bulk phase. This "unstirred layer", which contains stagnant solutes, may also exist between the bulk extracellular solution and membranes of other cells in an organism and may show different properties. On the other hand, an earlier study using a bacterial planar membrane indicated that H+released from a transporter migrates in the horizontal direction along the membrane surface much faster than it diffuses vertically toward the extracellular space. This result implies that between the membrane surface and unstirred layer, there is a "nanointerface" that has unique ionic dynamics. Advanced technologies have revealed that the nanointerface on artificial membranes possibly harbors a highly ordered assembly of water molecules. In general, hydrogen bonds are involved in formation of the ordered water structure and can mediate rapid transfer of H+between neighboring molecules. This description may match the phenomenon on the bacterial membrane. A recent study has suggested that water molecules in the nanointerface regulate the gating of K+channels. Here, the region comprising the unstirred layer and nanointerface is defined as the interphase between the plasma membrane and bulk extracellular solution (iMES). This article briefly describes the physicochemical properties of ions and water in the iMES and their physiological significance. We also describe the methodologies that are currently used or will be applicable to the interphase research.
authors.affiliation: Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Chuo-ku, Niigata, Niigata, 951-8510, Japan. hibinoh@med.niigata-u.ac.jp.|Center for Transdisciplinary Research, Niigata University, Niigata, Niigata, 950-2181, Japan. hibinoh@med.niigata-u.ac.jp.|AMED-CREST, AMED, Niigata, Japan. hibinoh@med.niigata-u.ac.jp.
authors.forename: Hiroshi
authors.identifier: http://orcid.org/0000-0003-0688-1489
authors.initials: H
authors.lastname: Hibino
authors.affiliation: Department of Bioengineering, School of Engineering, The University of Tokyo, Tokyo, Japan.
authors.forename: Madoka
authors.initials: M
authors.lastname: Takai
authors.affiliation: International Center for Materials Nanoarchitectonics and Global Research Center for Environment and Energy Based on Nanomaterials Science, National Institute for Materials Science, Tsukuba, Ibaraki, Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Noguchi
authors.affiliation: Department of Molecular Physiology, Niigata University School of Medicine, 1-757 Asahimachi-dori, Chuo-ku, Niigata, Niigata, 951-8510, Japan.
authors.forename: Seishiro
authors.initials: S
authors.lastname: Sawamura
authors.affiliation: Division of Electrical Engineering and Computer Science, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan.|Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Saitama, 332-0012, Japan.
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.affiliation: Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shiku
mesh_terms: D000818:Animals; D035843:Biomedical Research / Q000379:methods*; D002462:Cell Membrane / Q000378:metabolism*; D060833:Cellular Microenvironment; D045604:Extracellular Fluid / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport; D008567:Membranes, Artificial; D008954:Models, Biological; D050997:Nanomedicine; D014867:Water / Q000378:metabolism*
chemical_list: D008567:Membranes, Artificial; D014867:Water
keywords: Bulk extracellular fluid; Ions; Membrane; Nanointerface; Unstirred layer; Water