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Effects of Perfusion Rate on Permeability of Frog and Rat Mesenteric Microvessels to Sodium Fluorescein

2002; Wiley; Volume: 543; Issue: 3 Linguagem: Inglês

10.1113/jphysiol.2002.023010

1469-7793

D. Montermini, C.P. Winlove, C. C. Michel,

Hemoglobin structure and function

The permeability, P S , to sodium fluorescein (Stokes‐Einstein radius = 0.45 nm) has been measured in single mesenteric capillaries of pithed frogs and anaesthetised rats as perfusion velocity, U , was varied over a range from 400 up to 2000–10 000 μm s −1 . P S increased linearly with U . In 20 frog capillaries, mean (± S.E.M.) P S (in μm s −1 ) = 9.35 (± 1.55) U × 10 −5 + 0.244 (± 0.0291). Similarly, in nine rat venules, mean P S = 1.62 (± 0.385) U × 10 −4 + 0.375 (± 0.025). The flow‐dependent component of permeability could be reversibly abolished in frog capillaries by superfusing with 100 μM noradrenaline and by superfusing rat venules with the nitric oxide synthase inhibitor, N G ‐nitro‐L‐arginine (20 μM). It was shown that changes in microvascular pressure accompanying changes in U during free perfusion could account for only 15 % of the changes in P S , i.e. 85 % of the changes in P S were changes in the permeability coefficient itself. A comparison between the changes in P S with U and the previously described changes in microvascular permeability to K + with U , suggest that if the flow‐dependent component of permeability is modelled as a population of pores of constant size, these have radii of 0.8 nm. Such a pathway would limit flow‐dependent permeability to small hydrophilic molecules and have minimal effect on net fluid exchange.