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Openings in frog microvascular endothelium at different rates of increase in pressure and at different temperatures
Author(s) -
Savla U.,
Neal C. R.,
Michel C. C.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.012945
Subject(s) - chemistry , permeability (electromagnetism) , oncotic pressure , biophysics , elasticity (physics) , anatomy , albumin , materials science , biology , biochemistry , membrane , composite material
Experiments were carried out on single mesenteric capillaries and venules of pithed frogs to determine whether the rate of increase in intravascular pressure (d P /d t ) influenced the critical pressure ( P B ) which increases wall permeability. Vessels, microperfused with frog Ringer solutions containing 0.1 % bovine serum albumin and red cells, were occluded downstream before pressure was raised either as a ramp or in a series of 13.6 cmH 2 O steps. By varying step duration, the mean d P /d t could be matched to d P /d t applied as a steady ramp. P B was recorded as the pressure at which there was an abrupt increase in filtration with red cells passing to and through one or more sites in the vessel wall. In all vessels, increasing d P /d t raised P B , with no differences between steps and ramps. The relation between P B and d P /d t was linear, consistent with a latent period, T (the slope), between a critical pressure being reached and the abrupt increase in permeability being observed. Direct observation confirmed this latent period. Between 12 and 20 o C, T was 8.5 ± 0.47 s; between 0 and 5 °C, T was 11.5 ± 0.97 s. Tissue cooling did not influence the time constant, τ, describing the rate of stretch of wall following a step increase in pressure and used to measure wall visco‐elastic properties. Nor was the value of τ (1.15 ± 0.06 s, n = 42) consistent with T being accounted for by visco‐elasticity. It is suggested that the latent period may indicate an active response of the endothelium.