The filtration coefficients (Lp) of the walls of individually perfused frog mesenteric capillaries have been measured using the methods described by Michel et al. (1974). When a vessel was perfused with frog Ringer solution containing no protein, Lp was four to five times greater than its value for the same capillary perfused with frog plasma. The increase of Lp seen on perfusion with protein-free solutions was readily reversible and could be prevented by adding to the Ringer perfusate bovine serum albumin, bovine γ-globulin and human haemoglobin. The addition of whale myoglobin (0.5 g 100 ml-1) to the Ringer perfusate did not prevent an increase in Lp. Ringer solutions containing 0.1 g of bovine serum albumin 100 ml-1 were as effective as those containing higher concentrations of albumin in preventing the increase in Lp, but the Lp of capillaries perfused with solutions containing 0.01 g of albumin 100 ml-1 did not differ from the values for the same capillaries perfused with protein-free solutions. It was shown that in any given capillary, Lp was independent of the direction of fluid flow across the vessel wall and was the same when the capillary was perfused with 9.0 g of bovine albumin 100 ml-1 and 3 g of bovine γ-globulin 100 ml-1. Whereas the effects of Lp are seen within 1 min of removing the protein from the perfusate, no changes in Lp were observed during the first 20 min of perfusion and superfusion of capillaries with solutions free of Ca2+ and Mg2+. Lp also appeared to be unaffected after 20 min perfusion with neuraminidase. It is suggested that plasma proteins are adsorbed onto capillary walls and greatly modify capillary permeability.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine