Soluble complex of complement increases hydraulic conductivity in single microvessels of rat lung

We determined the effect of sera enriched with the soluble complex of complement (SC5b-9), on hydraulic conductivity (Lp) of single pulmonary venules (diameter 20-30 microns). Sera free of anticoagulants and blood cells were prepared from rat and human blood. Lp were determined by our split drop technique in isolated, blood-perfused lungs prepared from anesthetized rats (2% halothane; Sprague Dawley, 500 g; n = 73). Zymosan-activated (ZAS) and control sera were used for Lp determinations. In ZAS prepared from human serum, SC5b-9 concentration was > 300 micrograms/ml (control: < 1 microgram/ml) as determined by ELISA. At baseline, Lp averaged 3.4 +/- .4 x 10(-7) ml/(cm2.s.cm H2O), but it increased by 217 +/- 32% with undiluted ZAS (P < 0.05). The Lp increase correlated significantly with different ZAS dilutions for rat serum and with SC5b-9 concentration for human serum. Lp did not increase significantly with ZAS prepared from heat-treated sera, C6- and C8-deficient sera; or with ZAS in which SC5b-9 had been depleted by immunoprecipitation. The ZAS-induced increase of Lp was blocked completely by venular preinfusion with the arginine-glycine-aspartic acid (RGD) tripeptide (1 mg/ml, 10 min). We report for the first time that: (a) SC5b-9 increases lung endothelial Lp; and (b) the increase of Lp is attributable to an integrin-dependent mechanism.