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Permeability increase induced by light‐dye treatment

To investigate the effect of light‐dye treatment on permeability of mammalian microvessels, we measured hydraulic conductivity (Lp) of the post‐capillary venules of rat mesentery in vivo under various treatments. We perfused a single microvessel with sodium fluorescein (0.5mg/ml in 1%BSA mammalian Ringer). After control measurement, we exposed the vessel to the laser (495 nm, 2.2 mW), in 2–5 min after the laser treatment, Lp increased from a mean control of 0.84 (± 0.17 SE, n = 8) to a mean of 1.26 (± 0.09 SE) × 10−7 cm/s‐cmH2O, a 1.9 fold increase. Longer time exposure to the laser (up to 30 min) did not increase Lp further. To decrease the increased Lp by the light‐dye treatment, we pretreated the microvessel with a 2 mM cAMP analog, 8‐bromo‐cAMP, for 20 min. Lp decreased from a mean control of 1.40 (± 0.12 SE, n = 5) to a mean of 0.93 (± 0.08 SE) × 10−7 cm/s‐cmH2O in 20 min. Unexpectedly, cAMP did not decrease the Lp increase induced by the laser treatment. Instead, after 2–5min exposure to the laser, Lp increased to a mean of 4.13 (± 0.17 SE) × 10−7 cm/s‐cmH2O, a 3.6 (± 0.13 SE) fold increase from the control. We did not see the Lp decrease by cAMP in a longer time (30min) when exposure to the laser. One hypothesis for this is that the laser might change cAMP to cGMP, which was known to increase permeability. This work is in part supported by NSF.