The fractional volume occupied by extracellular space in tissues, termed a, is an important parameter of tissue architecture that affects cellular functions and drug delivery. We report a technically simple fluorescent dye partitioning method to measure a in tissue slices based on microfiberoptic detection of dye fluorescence in tissue versus overlying solution. Micro-fiberoptic tip geometry and dyes were selected for a determination from fluorescence intensity ratios, without the need to correct for illumination profile, light scattering/absorption, or dye binding. The method was validated experimentally using cell-embedded gels of specified α-values and optical properties. In mouse brain slices, a was strongly location-dependent, ranging from 0.16 in thalamus to 0.22 in brainstem, and was sensitive to cell volume changes. Aquaporin-4 water channel gene deletion caused significant extracellular space expansion, with α = 0.181 5 0.002 in cortex in wild-type mice and 0.211 ± 0.003 in Aqua-porin-4 knockout mice. In slices of LLC1 cell tumors grown in mice to ∼5 μm diameter, a decreased remarkably from ∼0.45 in superficial tumor to <0.25 in deeper (>100 μm) tumor. Fluorescent dye partitioning with microfiberoptic detection permits rapid, accurate, and anisotropy-insensitive determination of α-values in tissue slices. © 2010 by the Biophysical Society.
Zhang, H., & Verkman, A. S. (2010). Microfiberoptic measurement of extracellular space volume in brain and tumor slices based on fluorescent dye partitioning. Biophysical Journal, 99(4), 1284–1291. https://doi.org/10.1016/j.bpj.2010.06.023