Extracellular space volume measured by two-color pulsed dye infusion with microfiberoptic fluorescence photodetection

Mazin Magzoub, Hua Zhang, James A. Dix, A. S. Verkman

Research output: Contribution to journalArticlepeer-review

Abstract

The extracellular space (ECS) is the aqueous matrix surrounding cells in solid tissues. The only method to measure ECS volume fraction (α) in vivo has been tetramethylammonium iontophoresis, a technically challenging method developed more than 25 years ago. We report a simple, quantitative method to measure α by microfiberoptic fluorescence detection of a self-quenched green dye, calcein, and a reference red dye, sulforhodamine 101, after pulsed iontophoretic infusion. The idea is that the maximum increase in calcein fluorescence after iontophoresis is proportional to the aqueous volume into which the dye is deposited. We validated the method theoretically, and experimentally, using cell-embedded gels with specified a and ECS viscosity. Measurements in living mice gave α of 0.20±0.01 in brain, 0.13±0.02 in kidney and 0.074±0.01 in skeletal muscle. The technical simplicity of the "pulsed-infusion microfiberoptic photodetection" method developed here should allow elucidation of the relatively understudied biological roles of the ECS.

Original languageEnglish (US)
Pages (from-to)2382-2390
Number of pages9
JournalBiophysical journal
Volume96
Issue number6
DOIs
StatePublished - 2009

ASJC Scopus subject areas

  • Biophysics

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