title: Droplet-based microfluidic platform for measurement of rapid erythrocyte water transport.
abstract: Cell membrane water permeability is an important determinant of epithelial fluid secretion, tissue swelling, angiogenesis, tumor spread and other biological processes. Cellular water channels, aquaporins, are important drug targets. Water permeability is generally measured from the kinetics of cell volume change in response to an osmotic gradient. Here, we developed a microfluidic platform in which cells expressing a cytoplasmic, volume-sensing fluorescent dye are rapidly subjected to an osmotic gradient by solution mixing inside a ~0.1 nL droplet surrounded by oil. The solution mixing time was <10 ms. Osmotic water permeability was deduced from a single, time-integrated fluorescence image of an observation area in which the time after mixing was determined through spatial position. Water permeability was accurately measured in aquaporin-expressing erythrocytes with half-times for osmotic equilibration down to <50 ms. Compared with conventional water permeability measurements using costly stopped-flow instrumentation, the microfluidic platform here utilizes sub-microliter blood sample volume, does not suffer from mixing artifacts, and replaces challenging kinetic measurements by single image capture using a standard laboratory fluorescence microscope.
authors.affiliation: Departments of Medicine and Physiology, University of California, 1246 Health Sciences East Tower, San Francisco, CA 94143-0521, USA. Alan.Verkman@ucsf.edu.
authors.forename: Byung-Ju
authors.initials: BJ
authors.lastname: Jin
authors.forename: Cristina
authors.initials: C
authors.lastname: Esteva-Font
authors.forename: A S
authors.initials: AS
authors.lastname: Verkman
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000172:deficiency / Q000235:genetics; D002463:Cell Membrane Permeability; D004912:Erythrocytes / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D005452:Fluoresceins / Q000737:chemistry; D026901:Membrane Transport Proteins / Q000172:deficiency / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D008856:Microscopy, Fluorescence; D009821:Oils / Q000737:chemistry; D014867:Water / Q000737:chemistry / Q000378:metabolism*
chemical_list: D020346:Aquaporins; D005452:Fluoresceins; D026901:Membrane Transport Proteins; D009821:Oils; C452857:urea transporter B, mouse; D014867:Water; C007740:fluorexon