Figure 5.

Quantitative fluorescence imaging method for the measurement of solute permeability in a rat pial microvessel. The images were collected during the in vivo experiments and the fluorescence intensity was analyzed off-line. When the fluorescence labeled test solute was injected into the carotid artery, the pial microvessel lumen filled with fluorescent solute (red frame in b), producing ΔI₀. With continued perfusion, the measured fluorescence intensity increased indicating further transport of the solute out of the microvessel and into the surrounding tissue. The initial solute flux into the tissue was measured from the slope (dI/dt)₀ (a). The solute permeability P was calculated by P = 1/ΔI₀ (dI/dt)₀ r/2. Here r is the microvessel radius. Redrawn from [50]. The scale bar in (b) is 50 μm.